JP2019136619A - Honeycomb filter - Google Patents

Abstract

To provide a honeycomb filter capable of inexpensively and easily detecting the occurrence of cracks when the cracks occur by the excessive rise of temperature at the reproduction of the honeycomb filter.SOLUTION: In a honeycomb filter 100,: at least one of outer segments 7b has a protective layer having a thickness of 0.3 μm or less on the surface of a partition wall 1 or is a low heat resistant segment having no protective layer; an inner segment 7a and the outer segments 7b except the low heat resistant segment are highly heat resistant segments having a protective layer having a thickness of 0.5-7.3 μm on the surface of the partition wall 1; the protective layer contains silica of 40 mass% or more and oxygen of 40 mass% or more; and a ratio of the cross sectional area of the low heat resistant segment to the cross sectional area of all honeycomb segments 7 is 16-76%.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a honeycomb filter for removing particulate matter (particulate matter (hereinafter also referred to as “PM”)) in exhaust gas discharged from an internal combustion engine such as a diesel engine.

  Exhaust gas discharged from an internal combustion engine such as a diesel engine contains a large amount of PM such as soot containing carbon as a main component that causes environmental pollution. Therefore, a filter for removing (collecting) PM is generally mounted on an exhaust system such as a diesel engine.

  As a filter used for such a purpose, a honeycomb filter made of a ceramic material or the like is widely used. Usually, the honeycomb filter is composed of a honeycomb structure portion and a plugging portion. The honeycomb structure portion has porous partition walls that define a plurality of cells extending from an inflow end surface that is an end surface on the fluid inflow side to an outflow end surface that is an end surface on the fluid outflow side. A honeycomb filter is obtained by disposing a plugging portion that plugs one end portion of each cell on any end face of the honeycomb structure portion (see, for example, Patent Documents 1 and 2).

  When such a honeycomb filter is used for removing PM contained in the exhaust gas, the exhaust gas flows from the inflow end face of the honeycomb filter into a cell whose end is plugged at the outflow end face. Thereafter, the exhaust gas passes through the porous partition wall and moves into the cell whose end is plugged at the inflow end face. And when exhaust gas permeate | transmits a porous partition, this partition becomes a filtration layer, PM in exhaust gas is capture | acquired by the partition, and accumulates on a partition. Thus, the exhaust gas from which PM has been removed flows out from the outflow end face to the outside.

  By the way, in order to continuously use the honeycomb filter for a long period of time, it is necessary to periodically regenerate the filter. That is, in order to reduce the pressure loss increased by PM deposited over time on the partition walls of the honeycomb filter and return the filter performance to the initial state, it is necessary to burn and remove the PM deposited on the partition walls.

  The temperature of the honeycomb filter during regeneration is usually about 800 to 900 ° C. However, when PM is not sufficiently burned at the time of the previous regeneration and excessive PM is accumulated in the filter, the temperature of the honeycomb filter rises to about 1300 ° C., which is the heat resistant limit temperature, and the honeycomb filter Cracks may occur.

  If the honeycomb filter in which such a crack is generated is continuously used as it is, PM leaks from the crack and contaminates the environment. Therefore, a technique for detecting the occurrence of the crack is required.

  As a technique for detecting cracks in the honeycomb filter, an apparatus capable of detecting PM leaking from the cracks in the honeycomb filter may be disposed on the downstream side of the honeycomb filter. Conventionally, as a device that can detect PM, a PN measuring device that measures the number of particles of PM (PN: Particle Number) and a PM sensor that measures the weight of PM are known.

JP 57-7215 A JP 2000-279729 A

  However, in addition to being very expensive, the PN measuring device is so large that it is difficult to be mounted on a commercially available vehicle, so it is not realistic to detect the occurrence of cracks using this device. Further, when the crack generated in the honeycomb filter is minute, it is difficult for the PM sensor to detect the occurrence of the crack. That is, since PM that can leak out from a fine crack has a small particle size and is extremely lightweight, the sensitivity of a general PM sensor cannot detect an increase in weight due to PM leaking from the crack.

  In addition, it is conceivable to detect a crack in the honeycomb filter by a change in the pressure loss of the honeycomb filter. However, if the crack generated in the honeycomb filter is minute as described above, the change in the pressure loss is too small. Therefore, it is difficult to detect the occurrence of cracks.

  The present invention has been made in view of such conventional circumstances. That is, an object of the present invention is to provide a honeycomb filter capable of easily and inexpensively detecting the occurrence of a crack when a crack is generated due to excessive temperature rise during regeneration of the honeycomb filter.

  In order to achieve the above object, according to the present invention, the following honeycomb filter is provided.

[1] A honeycomb filter composed of a plurality of honeycomb segments,
The honeycomb segment has a porous partition wall that defines a plurality of cells serving as fluid flow paths extending from an inflow end surface that is an end surface on the fluid inflow side to an outflow end surface that is an end surface on the fluid outflow side. A structure portion, and a plugging portion disposed at one end of either the inflow end face side or the outflow end face side of the plurality of cells,
In the honeycomb filter, a plurality of honeycomb segments are combined in a direction perpendicular to the cell extending direction and joined and integrated.
The honeycomb structure part is composed of an aggregate made of silicon carbide, and a binder that bonds the aggregates together,
In the cross section orthogonal to the cell extending direction of the honeycomb filter, the honeycomb segment including at least a part thereof in a circle having a diameter of 3.6 cm centered on the center of gravity of the cross section is defined as an inner segment, and the other segments The honeycomb segment is the outer segment,
At least one of the outer segments has a protective layer having a thickness of 0.3 μm or less on the surface of the partition wall or is a low heat resistant segment having no protective layer,
Among the inner segment and the outer segment, those other than the low heat resistant segment are high heat resistant segments having a protective layer having a thickness of 0.5 to 7.3 μm on the surface of the partition wall,
The protective layer is a layer containing 40% by mass or more of silicon and 40% by mass or more of oxygen,
A honeycomb filter in which a ratio of a cross-sectional area of the low heat-resistant segment to a cross-sectional area of all the honeycomb segments in a cross section perpendicular to the cell extending direction of the honeycomb filter is 16 to 76%.

[2] The honeycomb filter according to [1], wherein the protective layer of the high heat resistant segment has a thickness of 1.0 to 6.0 μm.

[3] The ratio of the cross-sectional area of the low heat resistant segment to the cross-sectional area of all the honeycomb segments in the cross section perpendicular to the cell extending direction of the honeycomb filter is 32 to 66% [1] or [2 The honeycomb filter according to any one of the above.

[4] The honeycomb filter according to any one of [1] to [3], wherein the binder includes silicon or cordierite.

[5] The honeycomb filter according to any one of [1] to [4], wherein a catalyst is supported on the honeycomb structure part.

  In the honeycomb filter of the present invention, when the maximum temperature in the filter reaches a level at which cracks are generated, some of the honeycomb segments constituting the honeycomb filter become fibers by active oxidation and deform. Due to this deformation, a large crack is generated in the honeycomb filter so that even a PM having a relatively large particle size and a heavy weight can pass therethrough. For this reason, in the honeycomb filter of the present invention, it is easy to detect the PM leaking from the crack by the PM sensor and the change of the pressure loss due to deformation, without using an expensive and large PN measuring device. The occurrence of cracks can be easily detected.

1 is a perspective view schematically showing one embodiment of a honeycomb filter of the present invention. It is explanatory drawing which shows an inner segment and an outer segment in the cross section orthogonal to the cell extending direction of a honey-comb filter. It is explanatory drawing which shows an inner segment and an outer segment in the cross section orthogonal to the cell extending direction of a honey-comb filter. It is one Embodiment of a low heat resistant segment, Comprising: It is sectional drawing which shows typically a cross section parallel to the direction where a cell is extended. It is other embodiment of a low heat resistant segment, Comprising: It is sectional drawing which shows typically a cross section parallel to the direction where a cell is extended. It is one Embodiment of a high heat resistant segment, Comprising: It is sectional drawing which shows typically a cross section parallel to the direction where a cell is extended. It is explanatory drawing which shows the example of the combination of the high heat resistant segment and the low heat resistant segment in the honeycomb filter of this invention. It is explanatory drawing which shows the example of the combination of the high heat resistant segment and the low heat resistant segment in the honeycomb filter of this invention. It is explanatory drawing which shows the example of the combination of the high heat resistant segment and the low heat resistant segment in the honeycomb filter of this invention. It is explanatory drawing which shows the example of the combination of the high heat resistant segment and the low heat resistant segment in the honeycomb filter of this invention. It is explanatory drawing which shows the example of the combination of the high heat resistant segment and the low heat resistant segment in the honeycomb filter of this invention. It is explanatory drawing which shows the example of the combination of the high heat resistant segment and the low heat resistant segment in the honeycomb filter of this invention. It is explanatory drawing which shows the example of the combination of the high heat resistant segment and the low heat resistant segment in the honeycomb filter of this invention. It is explanatory drawing which shows the example of the combination of the high heat resistant segment and the low heat resistant segment in the honey-comb filter which does not satisfy | fill the requirements of this invention. It is explanatory drawing which shows the example of the combination of the high heat resistant segment and the low heat resistant segment in the honey-comb filter which does not satisfy | fill the requirements of this invention. 6 is a graph showing changes in pressure loss when the honeycomb filter is regenerated due to fiber formation when the honeycomb filter is regenerated with the engine in an idle state. 6 is a graph showing changes in pressure loss when the honeycomb filter is regenerated with the engine in an idle state and the honeycomb filter is not deformed due to fiber formation.

  Hereinafter, the present invention will be described based on specific embodiments. However, the present invention is not construed as being limited to these embodiments, and is within the scope of the present invention. Based on the knowledge, design changes and improvements can be added as appropriate.

(1) Honeycomb filter:
FIG. 1 is a perspective view schematically showing one embodiment of a honeycomb filter of the present invention. A honeycomb filter 100 according to an embodiment of the honeycomb filter of the present invention includes a plurality of honeycomb segments 7. The honeycomb segment 7 includes a honeycomb structure portion 4 and a plugging portion 3. The honeycomb structure 4 partitions and forms a plurality of cells 2 serving as a fluid flow path extending from an inflow end surface 11 which is an end surface on the side into which fluid such as exhaust gas flows into an outflow end surface 12 which is an end surface on the side from which fluid flows out. It has a porous partition wall 1. The plugging portion 3 is disposed at either one end of the plurality of cells 2 on the inflow end surface 11 side or the outflow end surface 12 side. The honeycomb filter 100 is configured by combining a plurality of honeycomb segments 7 in a direction perpendicular to the extending direction of the cells 2 and joining and integrating them through a joining material 8.

  A part of the plurality of honeycomb segments 7 constituting the honeycomb filter 100 is an inner segment 7a, and the remaining part is an outer segment 7b. 2 and 3 are explanatory diagrams showing the inner segment 7a and the outer segment 7b in a cross section orthogonal to the cell extending direction of the honeycomb filter 100. FIG. In these drawings, drawing of the partition walls and plugging portions of the honeycomb segment 7 is omitted.

  In the present invention, as shown in FIGS. 2 and 3, in a cross section perpendicular to the cell extending direction of the honeycomb filter 100, at least within a circle 13 having a diameter of 3.6 cm with the center of gravity G of the cross section as the center O. The honeycomb segment 7 including a part is defined as an inner segment 7a. Further, honeycomb segments other than the inner segment 7a are referred to as outer segments 7b. The “center of gravity” here refers to the center of gravity of the figure drawn by the outer peripheral edge of the honeycomb filter 100 in a cross section perpendicular to the extending direction of the cells 2 of the honeycomb filter 100. In the example of FIG. 2, among the 16 honeycomb segments 7 constituting the honeycomb filter 100, four honeycomb segments 7 at least part of which are included in the circle 13 are the inner segments 7 a, and the other 12 segments. The honeycomb segment 7 is the outer segment 7b. In the example of FIG. 3, of the 25 honeycomb segments 7 constituting the honeycomb filter 100, one honeycomb segment 7 at least part of which is included in the circle 13 is the inner segment 7 a, Twenty-four honeycomb segments 7 are the outer segments 7b.

  In the honeycomb filter 100, at least one of the outer segments 7b is a low heat resistant segment. Of the inner segment 7a and the outer segment 7b, those other than the low heat resistant segment are high heat resistant segments. Here, the low heat resistant segment is a honeycomb segment having a protective layer having a thickness of 0.3 μm or less on the surface of the partition wall or having no protective layer. Further, the high heat resistant segment is a honeycomb segment having a protective layer having a thickness of 0.5 to 7.3 μm on the surface of the partition wall. The protective layer is a layer containing 40% by mass or more of silicon and 40% by mass or more of oxygen.

  FIG. 4 is a cross-sectional view schematically showing a cross section parallel to the cell extending direction, which is an embodiment of the low heat resistant segment. FIG. 5 is a cross-sectional view schematically showing a cross section parallel to the cell extending direction according to another embodiment of the low heat resistance segment. FIG. 6 is a cross-sectional view schematically showing a cross section parallel to the cell extending direction, which is an embodiment of the high heat resistant segment.

  In one embodiment of the low heat resistant segment B shown in FIG. 4, a protective layer 6 having a thickness of 0.3 μm or less is formed on the surface of the partition wall 1. Further, in another embodiment of the low heat resistance segment B shown in FIG. 5, the protective layer is not formed on the surface of the partition wall 1, and the surface of the partition wall 1 is directly exposed in the cell 2. It has become. In one embodiment of the high heat resistant segment A shown in FIG. 6, a protective layer 5 having a thickness of 0.5 to 7.3 μm is formed on the surface of the partition wall 1.

  The structure other than the presence or absence of the protective layer and the thickness may be the same for the low heat resistant segment B and the high heat resistant segment A. That is, in both the low heat resistance segment B and the high heat resistance segment A, the honeycomb structure portion 4 includes the porous partition walls 1 that partition and form a plurality of cells 2 extending from the inflow end surface 11 to the outflow end surface 12. Some of the plurality of cells 2 are inlet plugged cells 2 b whose end portions are plugged by the plugged portions 3 on the inflow end face 11 side of the honeycomb structure portion 4. The remaining cells among the plurality of cells 2 are outlet plugged cells 2 a whose end portions are plugged by the plugged portions 3 on the outflow end face 12 side of the honeycomb structure portion 4. The outlet plugged cells 2a and the inlet plugged cells 2b are alternately arranged so as to be adjacent to each other with the partition wall 1 therebetween.

The protective layer 5 of the high heat resistant segment A is formed to suppress active oxidation of the high heat resistant segment A. Here, “active oxidation” is an oxidation decomposition reaction of silicon carbide that occurs when a silicon carbide material is exposed to a high temperature in a low oxygen atmosphere. Specifically, silicon monoxide (SiO) gas is generated from silicon carbide (SiC) as shown in the following formula (1). The SiO gas generated by this active oxidation is then combined with oxygen (O ₂ ) in the atmosphere to precipitate a fibrous substance (fiber) made of silicon dioxide (SiO ₂ ) as shown in the following formula (2). . Such a phenomenon is called “fibrosis”.
Formula (1): SiC (solid) + O ₂ (gas) → SiO (gas) + CO (gas)
Formula (2): SiO (gas) + 1 / 2O ₂ (gas) → SiO ₂ (solid)

  Even when the partition wall 1 has no protective layer or has the protective layer 6, the low heat resistant segment B having a thickness of 0.3 μm or less is as in the regeneration of the honeycomb filter 100. In such a low oxygen atmosphere, silicon carbide as an aggregate is actively oxidized at about 1200 ° C. And when fiberization arises by this active oxidation, the low heat resistant segment B will deform | transform and a big crack will generate | occur | produce in connection with it. Further, in the initial stage of fiber formation, the flow path (cell) is narrowed due to the deformation of the low heat resistance segment B, and the pressure loss temporarily increases.

  On the other hand, in the high heat resistant segment A having the protective layer 5 having a thickness of 0.5 to 7.3 μm on the surface of the partition wall 1, even in a low oxygen atmosphere such as during regeneration of the honeycomb filter 100, 1300 Active oxidation does not occur up to about ℃, and fiberization does not occur. That is, the temperature at which cracks occur in the high heat resistant segment A is about 1300 ° C., which is about 100 ° C. higher than the temperature at which the low heat resistant segment B is fiberized.

  7 to 13 are explanatory views showing examples of combinations of the high heat resistance segment A and the low heat resistance segment B in the honeycomb filter 100 of the present invention. In these drawings, drawing of the partition walls and plugging portions of the honeycomb segment is omitted. In these drawings, the honeycomb segment surrounded by a dotted line is an inner segment, and the other honeycomb segments are outer segments.

  In the example of FIG. 7, of the 16 honeycomb segments constituting the honeycomb filter 100, only 4 inner segments are the high heat resistant segments A, and 12 outer segments are all the low heat resistant segments B. In the example of FIG. 8, of the 16 honeycomb segments constituting the honeycomb filter 100, 4 inner segments and 4 outer segments are the high heat resistance segments A, and 8 outer segments are the low heat resistance. Segment B. In the example of FIG. 9, among the 16 honeycomb segments constituting the honeycomb filter 100, 4 inner segments and 9 outer segments are high heat resistant segments A, and 3 outer segments are low heat resistant. Segment B. In the example of FIG. 10, of the 16 honeycomb segments constituting the honeycomb filter 100, 4 inner segments and 6 outer segments are high heat resistant segments A, and 6 outer segments are low heat resistant. Segment B.

  In the example of FIG. 11, of the 25 honeycomb segments constituting the honeycomb filter 100, one inner segment and four outer segments are the high heat resistance segment A, and the twenty outer segments are low. This is the heat resistant segment B. In the example of FIG. 12, among the 25 honeycomb segments constituting the honeycomb filter 100, one inner segment and eight outer segments are the high heat resistance segment A, and 16 outer segments are the low heat resistance. Segment B. In the example of FIG. 13, of the 25 honeycomb segments constituting the honeycomb filter 100, one inner segment and 15 outer segments are the high heat resistance segment A, and nine outer segments are the low heat resistance. Segment B.

  According to a study by the present inventors, when the honeycomb filter 100 is regenerated, when the temperature in the vicinity of the center (the vicinity where the inner segment is disposed) that is the highest temperature reaches about 1300 ° C., the lowest temperature is obtained. It reaches about 1200 ° C even near the outer periphery. For this reason, when the high heat resistance segment A reaches a temperature at which cracking occurs (about 1300 ° C.), the low heat resistance segment B reaches the temperature at which active oxidation occurs (about 1200 ° C.), and the fiber Deformation has started. That is, in the honeycomb filter 100 in which at least one of the outer segments is the low heat resistant segment B, when the high heat resistant segment A reaches a temperature at which cracking occurs, the outer segment (low heat resistant segment B) is reached. ) Will be deformed. Due to the deformation due to the fiber formation, a large crack is generated in the honeycomb filter 100 so that even a PM having a relatively large particle size and a heavy weight can be passed. Further, in the initial stage of fiber formation, the flow path (cell) is narrowed due to the deformation of the low heat resistance segment B, and the pressure loss temporarily increases.

  As described above, the honeycomb filter 100 has a low heat resistance such that a large crack is generated when the high heat resistance segment A reaches a temperature at which a crack is generated as a part of a plurality of honeycomb segments constituting the honeycomb filter 100. Sex segment B is intentionally included. Therefore, in the honeycomb filter 100 of the present invention, it is easy to detect the PM leaking from the crack by the PM sensor and the change of the pressure loss due to deformation, and it is not necessary to use an expensive and large PN measuring device. Also, the occurrence of cracks can be easily detected.

  The arrangement and number of the low heat-resistant segments B and the high heat-resistant segments A in the honeycomb filter 100 are not limited to the examples shown in FIGS. However, the ratio of the cross-sectional area of the low heat resistant segment B to the cross sectional area of all the honeycomb segments (high heat resistant segment A and low heat resistant segment B) in the cross section perpendicular to the cell extending direction of the honeycomb filter 100 is 16 to 76. %, Preferably 32 to 66%. If this ratio is less than 16%, the occurrence of cracks may be difficult to detect. On the other hand, if this ratio exceeds 76%, the amount of PM that can be burned without causing cracks during regeneration may be too small. FIG. 14 is an explanatory diagram showing an example of a combination of a low heat resistant segment and a high heat resistant segment in a honeycomb filter that does not satisfy the requirements of the present invention. In the example of FIG. 14, of the 25 honeycomb segments constituting the honeycomb filter 200, only one inner segment is the high heat resistant segment A, and 24 outer segments are all the low heat resistant segment B, The ratio is over 76%. FIG. 15 is also an explanatory diagram showing an example of a combination of a low heat resistant segment and a high heat resistant segment in a honeycomb filter that does not satisfy the requirements of the present invention. In the example of FIG. 15, among the 16 honeycomb segments constituting the honeycomb filter 300, 4 inner segments are the low heat resistant segments B and 12 outer segments are the high heat resistant segments A.

  The thickness of the protective layer 5 formed on the surface of the partition wall 1 of the high heat resistant segment A as shown in FIG. 6 is 0.5 to 7.3 μm, and preferably 1.0 to 6.0 μm. If the thickness of the protective layer 5 is less than 0.5 μm, the active oxidation of the high heat resistant segment A cannot be sufficiently suppressed, and the amount of PM that can be burned without generating cracks during regeneration is small. It may become too much. On the other hand, if the thickness of the protective layer exceeds 7.3 μm, the thermal expansion coefficient increases and the thermal stress generated during regeneration increases and cracks are likely to occur. In some cases, the amount of PM that can be reduced becomes too small.

  The low heat resistant segment B as shown in FIG. 5 has a protective layer formed on the surface of the partition wall 1 or, for example, even if the protective layer 6 as shown in FIG. 0.3 μm or less. If the protective layer 6 having a thickness of more than 0.3 μm is formed on the surface of the partition wall 1 of the low heat resistant segment B, the low heat resistant segment A will have a low heat resistance even when the high heat resistant segment A reaches a cracking level. There is a case where the deformation due to the fiber formation and the accompanying crack do not occur in the sex segment B.

  The protective layer contains 40% by mass or more of silicon and 40% by mass or more of oxygen. By forming a protective layer containing 40% by mass or more of silicon and 40% by mass or more of oxygen on the surface of the partition wall 1 of the high heat resistant segment A so as to have a thickness of 0.5 to 7.3 μm, Active oxidation of the heat resistant segment A can be effectively suppressed. When at least one of silicon and oxygen contained in the protective layer is less than 40% by mass, even if the protective layer having the above thickness is formed on the surface of the partition wall 1 of the high heat resistant segment A, the high heat resistance The active oxidation of the sex segment A cannot be sufficiently suppressed. The protective layer preferably contains 49% by mass or more of silicon and 42% by mass or more of oxygen, more preferably contains 50% by mass or more of silicon and 43% by mass or more of oxygen, and 53% by mass. More preferably, it contains the above silicon and 46 mass% or more oxygen.

As a method for forming such a protective layer, for example, a honeycomb segment whose aggregate is silicon carbide is heated at 900 to 1400 ° C. for about 5 to 20 hours in an oxygen atmosphere (for example, an oxygen concentration of 15 to 20 mass%). The method of doing is mentioned. By oxidizing the honeycomb segment by such a method, a part of the silicon carbide as the aggregate is oxidized, and the silica (SiO ₂ ) material containing 40% by mass or more of silicon and 40% by mass or more of oxygen. A protective layer (oxide film) is formed.

  In addition, confirmation of the presence or absence of a protective layer and the measurement of the thickness of a protective layer can be performed using FE-EPMA (field emission type electron beam microanalyzer). Specifically, first, a layer (protective layer) containing 40% by mass or more of silicon and 40% by mass or more of oxygen covering the SiC particles (aggregate) constituting the partition walls of the honeycomb segment by FE-EPMA. Check if there is any. Next, five fields of view having a length of 100 μm × width of 100 μm are randomly extracted from the partition wall on which the protective layer has been confirmed to be formed. Then, for each field of view, the protective layer covering the SiC particles (aggregate) is randomly extracted at 10 locations to measure the thickness, and the average thickness of the total 50 locations is taken as the thickness of the protective layer. To do.

  The honeycomb structure 4 of the honeycomb filter 100 as shown in FIG. 1 is composed of an aggregate made of silicon carbide (SiC) and a binder that bonds the aggregates together. The binding material preferably contains silicon (Si) or cordierite. When the binder contains silicon, high thermal conductivity is obtained, and the temperature during filter regeneration can be suppressed. Moreover, when a binder contains cordierite, a thermal expansion coefficient becomes low and it becomes difficult to generate | occur | produce a crack.

  As the material constituting the plugged portion 3, it is preferable to use the same material as the material constituting the honeycomb structured portion 4 in order to reduce the difference in thermal expansion between the plugged portion 3 and the honeycomb structured portion 4. The length of the plugged portions 3 in the extending direction of the cells 2 (depth of the plugged portions 3) is not particularly limited, and can be appropriately determined according to the use environment of the honeycomb filter 100 or the like.

  The thickness of the partition wall 1 is preferably 50 to 500 μm, and particularly preferably 100 to 400 μm. When the thickness of the partition wall 1 is less than 50 μm, sufficient strength may not be obtained. Moreover, when the thickness of the partition wall 1 exceeds 500 μm, the pressure loss becomes too high, and when the honeycomb filter 100 is mounted on an exhaust system such as a diesel engine, the engine output may be reduced.

  The porosity of the partition wall 1 is preferably 25 to 80%, more preferably 30 to 76%, and particularly preferably 35 to 72%. When the porosity of the partition wall 1 is less than 25%, the pressure loss becomes too high, and when the honeycomb filter 100 is mounted on an exhaust system such as a diesel engine, the engine output may be reduced. Further, if the porosity of the partition wall 1 exceeds 80%, sufficient strength may not be obtained. The “porosity” referred to here is a value measured by a mercury porosimeter.

  The average pore diameter of the partition wall 1 is preferably 5 to 100 μm, more preferably 7 to 80 μm, and particularly preferably 9 to 50 μm. When the average pore diameter of the partition wall 1 is less than 5 μm, the pressure loss becomes too high, and when the honeycomb filter 100 is mounted on an exhaust system such as a diesel engine, the engine output may be reduced. Moreover, when the average pore diameter of the partition walls exceeds 100 μm, sufficient strength may not be obtained. Here, the “average pore diameter” is a value measured by a mercury porosimeter.

Cell density of the honeycomb structured portion 4 is preferably 15 to 650 cells / cm ^2, more preferably from 30 to 550 cells / cm ^2. When the cell density of the honeycomb structure portion 4 is less than 15 cells / cm ² , the strength and effective filtration area of the honeycomb filter 100 may be insufficient. Further, when the cell density of the honeycomb structure part 4 exceeds 650 cells / cm ² , the distance between the partition walls 1 surrounding the cell 2 is shortened, so that PM may be clogged in the flow path (cell 2).

  There is no particular limitation on the cell shape of the honeycomb structure portion 4 (the shape of the cell 2 in the cross section orthogonal to the direction in which the cells 2 extend). Preferred cell shapes include triangles, quadrilaterals, pentagons, hexagons, octagons and other polygons, circles, ellipses, or combinations thereof. Among the squares, a square or a rectangle is preferable.

  The overall shape of the honeycomb filter 100 is not particularly limited. Preferable overall shape of the honeycomb filter 100 includes a columnar shape, a columnar shape having an elliptical end surface, a polygonal columnar shape such as a square, rectangular, triangular, pentagonal, hexagonal or octagonal end surface. Note that the honeycomb filter 100 shown in FIG. 1 has a cylindrical shape.

  An outer peripheral coat layer 9 may be formed on the honeycomb filter 100. The thickness of the outer peripheral coat layer 9 is preferably 0.05 to 3.0 mm, and more preferably 0.1 to 1.5 mm. If the thickness of the outer peripheral coat layer 9 is less than 0.05 mm, the strength of the outer peripheral coat layer 9 may be insufficient, and the outer peripheral coat layer 9 may be easily broken. Further, if the thickness of the outer peripheral coat layer 9 exceeds 3.0 mm, the pressure loss may become too high.

  It is preferable that a catalyst is supported on the honeycomb structure portion 4. By supporting the catalyst, it is possible to promote the combustion of PM during regeneration or to purify harmful components contained in the exhaust gas. Examples of the catalyst include an oxidation catalyst, a three-way catalyst, and a reduction catalyst.

  The amount of the catalyst supported is preferably 10 to 500 g / L, more preferably 20 to 400 g / L, and particularly preferably 30 to 300 g / L. If the catalyst loading is less than 10 g / L, the catalyst performance may not be sufficiently exhibited. On the other hand, if the amount of the catalyst supported exceeds 500 g / L, the cross-sectional area of the flow path (cell) becomes small and the pressure loss may become too high. The catalyst loading (g / L) referred to here is the amount (g) of the catalyst supported per unit volume (1 L) of the honeycomb structure portion.

(2) Manufacturing method of honeycomb filter:
Hereinafter, an example of the manufacturing method of the honeycomb filter of the present invention will be described. First, a forming raw material containing a ceramic raw material is prepared. The ceramic raw material is preferably composed of silicon carbide as an aggregate and silicon or cordierite forming raw material as a binder. The cordierite forming raw material is a raw material that becomes cordierite by being fired. Specifically, silica is 42 to 56% by mass, alumina is 30 to 45% by mass, and magnesia is 12 to 16%. It is a raw material blended to have a chemical composition that falls within the range of mass%.

  The forming raw material is preferably prepared by mixing the ceramic raw material with a dispersion medium, a sintering aid, an organic binder, a surfactant, a pore former, and the like.

  It is preferable to use water as the dispersion medium. The content of the dispersion medium is appropriately adjusted so that the clay obtained by kneading the molding raw material has a hardness that facilitates molding. The specific content of the dispersion medium is preferably 20 to 80% by mass with respect to the entire forming raw material.

  As a sintering aid, for example, yttria, magnesia, strontium oxide and the like can be used. The content of the sintering aid is preferably 0.1 to 0.3% by mass with respect to the entire forming raw material.

  Examples of the organic binder include methyl cellulose, hydroxypropoxyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, and polyvinyl alcohol. Among these, it is preferable to use methyl cellulose and hydroxypropoxyl cellulose in combination. The content of the organic binder is preferably 2 to 10% by mass with respect to the entire forming raw material.

  As the surfactant, ethylene glycol, dextrin, fatty acid soap, polyalcohol and the like can be used. These may be used individually by 1 type and may be used in combination of 2 or more type. The content of the surfactant is preferably 2% by mass or less with respect to the whole forming raw material.

  The pore former is not particularly limited as long as it becomes pores after firing, and examples thereof include graphite, starch, foamed resin, hollow resin, water absorbent resin, and silica gel. The pore former content is preferably 10% by mass or less based on the entire forming raw material.

  Next, the forming raw material is kneaded to form a clay. There is no particular limitation on the method of kneading the forming raw material to form the clay. For example, a method using a kneader, a vacuum kneader or the like can be mentioned.

  Next, the obtained kneaded material is formed to form a honeycomb formed body. A honeycomb formed body is a formed body having partition walls that partition and form a plurality of cells that serve as fluid flow paths. The method for forming the kneaded clay to form the honeycomb formed body is not particularly limited, and a known molding method such as an extrusion molding method or an injection molding method can be used. For example, a method of extruding using a die corresponding to a desired cell shape, partition wall thickness, etc. can be mentioned as a suitable example. As the material of the die, a cemented carbide which does not easily wear is preferable.

  The honeycomb formed body thus obtained is dried and then fired. Examples of the drying method include hot air drying, microwave drying, dielectric drying, reduced pressure drying, vacuum drying, freeze drying, and the like. Among them, it is preferable to perform dielectric drying, microwave drying, or hot air drying alone or in combination.

  The dried honeycomb formed body (honeycomb dried body) is fired to produce a honeycomb structure part. In addition, before this firing (main firing), it is preferable to perform calcination (degreasing) in order to remove the binder and the like contained in the honeycomb formed body. The conditions for the calcination are not particularly limited as long as the organic substances (organic binder, surfactant, pore former, etc.) contained in the honeycomb formed body can be removed. Generally, the combustion temperature of the organic binder is about 100 to 300 ° C., and the combustion temperature of the pore former is about 200 to 800 ° C. Therefore, it is preferable to heat at about 200 to 1000 ° C. for about 3 to 100 hours in an oxidizing atmosphere as a condition for calcination.

  The firing (main firing) of the honeycomb formed body is performed to sinter and densify the forming raw material constituting the calcined honeycomb formed body to ensure a predetermined strength. Since the firing conditions (temperature, time, atmosphere, etc.) vary depending on the type of the forming raw material, appropriate conditions may be selected according to the type.

  Next, plugging portions are formed in the honeycomb structure portion. The outlet plugging cell is formed so that the end is plugged on the outflow end face side of the honeycomb structure part with respect to the outlet plugged cell, and the inflow end face of the honeycomb structure part is provided with respect to the inlet plugged cell. On the side, the end portion is plugged. A conventionally known method can be used for forming the plugged portion. As an example of a specific method, first, a sheet is attached to the end face of the honeycomb structure manufactured by the above method. Next, a hole is made in the sheet at a position corresponding to the cell in which the plugging portion is to be formed. Next, with the sheet attached, the end face of the honeycomb structure portion is immersed in a plugging slurry in which the plugging portion forming material is slurried, and the plugging is made through the holes formed in the sheet. The plugging slurry is filled into the open end of the cell to be stopped.

  Thus, the plugging slurry filled in the cells is dried and then fired and cured to obtain a honeycomb segment having a honeycomb structure portion and a plugging portion. It is preferable to use the same material as the formation material of the honeycomb structure portion as the formation material of the plugging portion. The plugging portion may be formed at any stage after the honeycomb formed body is dried, after calcining, or after firing (main firing).

Of the honeycomb segments obtained in this way, those having high heat resistance are subjected to an oxidation treatment for forming a protective layer. Examples of the oxidation treatment method include a method in which the honeycomb segment is heated at 900 to 1400 ° C. for about 5 to 20 hours in an oxygen atmosphere (for example, an oxygen concentration of 15 to 20% by mass). By oxidizing the honeycomb segment by such a method, a part of the silicon carbide as an aggregate is oxidized, and silica containing 40% by mass or more of silicon and 40% by mass or more of oxygen on the surface of the partition wall A protective layer (oxide film) of (SiO ₂ ) quality is formed.

  Of the honeycomb segments obtained as described above, those having a low heat resistance segment basically do not need a protective layer, and therefore need not be subjected to oxidation treatment. However, even if it is a low heat-resistant segment, as long as the thickness is less than 0.3 μm, a protective layer may be formed on the surface of the partition wall. A protective layer having a thickness of less than 0.3 μm may be formed in the course of firing (main firing) of the above-described honeycomb molded body without any particular oxidation treatment. When a protective layer having a thickness of less than 0.3 μm is formed by oxidation treatment, the oxygen concentration in the heating atmosphere is reduced or the heating time is shortened compared with the case where the protective layer of the high heat resistant segment is formed. It is preferable to adjust the thickness of the protective layer to be formed.

  Next, a slurry-like bonding material is applied to each side surface of the high heat resistance segment and the low heat resistance segment, and the high heat resistance segment and the low heat resistance segment are bonded so that the side surfaces are bonded to each other by the bonding material. And combine. At this time, at least one of the outer segments is a low heat resistant segment. Further, the high heat-resistant segment so that the ratio of the cross-sectional area of the low heat-resistant segment to the cross-sectional area of all the honeycomb segments in the cross-section orthogonal to the cell extending direction of the finally obtained honeycomb filter is 16 to 76%. And the number of low heat resistant segments. By combining the high heat resistance segment and the low heat resistance segment in this way and heating and drying the bonding material, a plurality of honeycomb segments (high heat resistance segment and low heat resistance segment) are bonded and integrated through the bonding material. A bonded honeycomb segment assembly is obtained.

  As the bonding material, for example, an inorganic raw material such as inorganic fiber, colloidal silica, clay, ceramic particles, etc., and an additive such as an organic binder, a foamed resin, a dispersing agent and water are added and kneaded to form a slurry. Can be preferably used. The method for applying the bonding material to the respective side surfaces of the high heat resistant segment and the low heat resistant segment is not particularly limited, and a method such as brush coating can be used.

  The honeycomb segment bonded body can be used as it is as a honeycomb filter, but if necessary, the outer peripheral portion thereof may be ground to have a desired shape such as a columnar shape. In this case, it is preferable to form an outer peripheral coat layer on the outer peripheral portion (processed surface) after grinding.

  The outer peripheral coating layer is formed by applying an outer peripheral coating material to the processed surface of the joined honeycomb segment assembly after grinding. As the outer periphery coating material, an inorganic raw material machine binder such as inorganic fiber, colloidal silica, clay, ceramic particles, an additive material such as a foamed resin, a dispersant and the like are kneaded and kneaded to form a slurry. it can. The method for applying the outer periphery coating material to the processed surface of the honeycomb bonded body is not particularly limited. As a preferable method, for example, a method of coating the outer peripheral coating material with a rubber spatula or the like on the processed surface while rotating the joined honeycomb segment assembly after grinding on the wheel.

(3) Catalyst loading method:
Next, an example of a method for supporting the catalyst on the honeycomb structure part of the honeycomb filter manufactured as described above will be described. First, a catalyst slurry containing a catalyst to be supported is prepared. The catalyst slurry is coated on the partition walls of the honeycomb structure. The coating method is not particularly limited. For example, a preferable coating method is a method (suction method) of sucking from the other end surface of the honeycomb structure portion while one end surface of the honeycomb structure portion is immersed in the catalyst slurry. Thus, after the catalyst slurry is coated on the partition walls of the honeycomb structure portion, the catalyst slurry is dried. Further, the dried catalyst slurry may be fired. In this way, a honeycomb filter having an oxidation catalyst supported on the honeycomb structure part can be obtained.

  EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, this invention is not limited to these Examples.

Example 1
Silicon carbide (SiC) powder and metal silicon (Si) powder were mixed at a mass ratio of 80:20 to obtain a ceramic raw material. To the obtained ceramic raw material, hydroxypropylmethylcellulose as an organic binder and a water-absorbing resin as a pore-forming material are added, and water is added as a dispersion medium to form a forming raw material. This forming raw material is kneaded with a vacuum kneader. A clay was made. The amount of the organic binder added was 7 parts by mass with respect to 100 parts by mass of the ceramic raw material. The addition amount of the pore former was 3 parts by mass with respect to 100 parts by mass of the ceramic raw material. The amount of water added was 42 parts by mass with respect to 100 parts by mass of the ceramic raw material.

  The obtained kneaded material was extruded using a die having a predetermined shape to obtain a honeycomb formed body having an overall shape of a quadrangular prism. The honeycomb formed body thus obtained was dried with a microwave dryer and then further dried with a hot air dryer to obtain a dried honeycomb body.

  Next, plugged portions were formed at one end of predetermined cells of the dried honeycomb body and the other end of the remaining cells. The plugged portions are formed in a checkered pattern on both end faces of the dried honeycomb body, with cells having plugged portions formed at the end portions and cells without plugged portions formed at the end portions. Went so. As a method for forming the plugged portions, first, a sheet was attached to the end face of the dried honeycomb body, and holes were formed in the sheet at positions corresponding to the cells where the plugged portions were to be formed. Subsequently, with the sheet attached, the end face of the dried honeycomb body is immersed in a plugging slurry in which the forming material of the plugging portion is slurried, and the plugs are sealed through holes formed in the sheet. The plugging slurry was filled into the end of the cell to be stopped. In addition, the same material as the molding raw material was used as a material for forming the plugging portion.

  Thus, after the plugging slurry filled in the end portion of the cell was dried, the dried honeycomb body was calcined (degreasing) at about 400 ° C. in an air atmosphere. Then, the honeycomb segment was obtained by firing at about 1450 ° C. in an Ar inert atmosphere. The obtained honeycomb segment had a square shape with a cross section perpendicular to the cell extending direction having a side of 36 mm, and the length in the cell extending direction was 152 mm. Further, the honeycomb structure portion of the obtained honeycomb segment was composed of an aggregate made of silicon carbide and a binder made of silicon and bonding the aggregates together.

A part of the plurality of honeycomb segments thus obtained was subjected to oxidation treatment, and the partition wall surface had a thickness of 1.5 μm, 53 mass% silicon and 46 mass% oxygen. An SiO ₂ protective layer (oxide film) containing The oxidation treatment was performed by heating the honeycomb segment at 1300 ° C. for 5 hours in an oxygen atmosphere having an oxygen concentration of 20 mass%. The honeycomb segments thus subjected to oxidation treatment were designated as high heat resistance segments, and the honeycomb segments not subjected to oxidation treatment were designated as low heat resistance segments.

  Subsequently, silica fiber, an organic binder, and water were added to the alumina powder to obtain a slurry-like bonding material. This bonding material was applied to each side surface of the high heat resistant segment and the low heat resistant segment so as to have a thickness of about 1 mm. Then, a total of 16 honeycomb segments composed of the four high heat resistant segments A and the 12 low heat resistant segments B to which the bonding material is applied in this way are combined so as to have the arrangement shown in FIG. A honeycomb segment laminate was produced. This honeycomb segment laminated body was dried at 120 ° C. for 2 hours to obtain a bonded honeycomb segment assembly having an overall shape of a quadrangular prism.

  Next, the outer periphery was ground so that the overall shape of the joined honeycomb segment assembly was a columnar shape. After grinding, an outer periphery coating material having the same composition as the bonding material was applied to the processed surface with a thickness of 1 mm and dried and cured at 700 ° C. for 2 hours to form an outer periphery coating layer.

The honeycomb filter of Example 1 manufactured in this way had a diameter of 144 mm and a length of 152 mm. The partition wall thickness was 320 μm, and the partition wall porosity was 52%. The cell density was 46 cells / cm ² and the cell shape was square. The ratio of the cross sectional area of the low heat resistant segment to the cross sectional area of all the honeycomb segments (high heat resistant segment and low heat resistant segment) in the cross section perpendicular to the cell extending direction of the honeycomb filter was 66%.

(Examples 2-4, 6-8)
Similar to Example 1 except that the content of silicon and oxygen and / or the thickness of the protective layer in the protective layer of the high heat resistance segment was changed to the values shown in Table 1 by adjusting the conditions of the oxidation treatment. Thus, honeycomb filters of Examples 2 to 4 and 6 to 8 were produced.

(Example 5)
A honeycomb filter of Example 5 was produced in the same manner as Example 1 except that the catalyst was supported on the honeycomb structure portion of each honeycomb segment. The catalyst is supported by forming a coating layer of a catalyst slurry containing platinum (Pt) and rhodium (Rh) in a ratio of 5: 1 on the surface of the partition walls of the joined honeycomb segment assembly by a suction method. This was done by drying. The total supported amount of precious metals (Pt, Rh) per liter of the honeycomb filter was 15 g.

Example 9
As the low heat resistant segment, a partition wall having a thickness of 0.3 μm and a SiO ₂ protective layer (oxide film) containing 50 mass% silicon and 43 mass% oxygen was used. Except for the above, a honeycomb filter of Example 9 was produced in the same manner as Example 1.

(Example 10)
A honeycomb filter of Example 10 was produced in the same manner as Example 4 except that the metal silicon powder of the ceramic raw material was changed to a cordierite forming raw material.

(Example 11)
Example 10 except that the thickness of the protective layer of the high heat resistant segment was changed to the value shown in Table 1 by adjusting the conditions of the oxidation treatment, and the catalyst was supported on the honeycomb structure portion of each honeycomb segment. In the same manner as described above, a honeycomb filter of Example 11 was produced. The catalyst is supported by forming a catalyst slurry coat layer containing platinum (Pt) and rhodium (Rh) in a ratio of 5: 1 on the surface of the partition walls of the joined honeycomb segment assembly by a suction method, and then heating. This was done by drying. The total supported amount of precious metals (Pt, Rh) per liter of the honeycomb filter was 15 g.

Example 12
Except for combining a total of 16 honeycomb segments composed of 13 high heat resistant segments A and 3 low heat resistant segments B so as to be arranged as shown in FIG. 9, the same as in Example 2, A honeycomb filter of Example 12 was produced. The ratio of the cross-sectional area of the low heat-resistant segment to the cross-sectional area of all the honeycomb segments (high heat-resistant segment and low heat-resistant segment) in the cross section perpendicular to the cell extending direction of the honeycomb filter was 16%.

(Example 13)
Except for combining a total of 16 honeycomb segments composed of 10 high heat resistant segments A and 6 low heat resistant segments B so as to be arranged as shown in FIG. A honeycomb filter of Example 13 was produced. The ratio of the cross-sectional area of the low heat-resistant segment to the cross-sectional area of all the honeycomb segments (high heat-resistant segment and low heat-resistant segment) in the cross section perpendicular to the cell extending direction of the honeycomb filter was 32%.

(Example 14)
Except for combining a total of 25 honeycomb segments composed of 5 high heat resistant segments A and 20 low heat resistant segments B so as to be arranged as shown in FIG. 11, the same as in Example 1, A honeycomb filter of Example 14 was produced. However, the used honeycomb segment had a cross section perpendicular to the cell extending direction and was a square having a side of 39 mm, and the length in the cell extending direction was 152 mm. The honeycomb filter had a diameter of 191 mm and a length of 152 mm. The ratio of the cross-sectional area of the low heat-resistant segment to the cross-sectional area of all the honeycomb segments (high heat-resistant segment and low heat-resistant segment) in the cross section perpendicular to the cell extending direction of the honeycomb filter was 76%.

(Example 15)
Except for combining a total of 25 honeycomb segments composed of 9 high heat resistant segments A and 16 low heat resistant segments B so as to be arranged as shown in FIG. 12, the same as in Example 1, A honeycomb filter of Example 15 was produced. However, the used honeycomb segment had a cross section perpendicular to the cell extending direction and was a square having a side of 39 mm, and the length in the cell extending direction was 152 mm. The honeycomb filter had a diameter of 191 mm and a length of 152 mm. The ratio of the cross-sectional area of the low heat-resistant segment to the cross-sectional area of all the honeycomb segments (high heat-resistant segment and low heat-resistant segment) in the cross section perpendicular to the cell extending direction of the honeycomb filter was 56%.

(Comparative Example 1)
A honeycomb filter of Comparative Example 1 was produced in the same manner as in Example 1 except that all of the 16 honeycomb segments were low heat resistant segments.

(Comparative Example 2)
Except for combining a total of 16 honeycomb segments composed of 12 high heat resistant segments A and 4 low heat resistant segments B so as to be arranged as shown in FIG. 15, the same as in Example 1, A honeycomb filter of Comparative Example 2 was produced. In the honeycomb filter of Comparative Example 2, four inner segments are low heat resistant segments B, and twelve outer segments are high heat resistant segments A.

(Comparative Example 3)
The honeycomb of Comparative Example 3 was prepared in the same manner as in Example 1 except that the content of silicon and oxygen in the protective layer of the high heat resistant segment was changed to the values shown in Table 1 by adjusting the conditions for the oxidation treatment. A filter was produced.

(Comparative Example 4)
A honeycomb filter of Comparative Example 4 was produced in the same manner as in Example 1 except that four low heat resistant segments A were used instead of the four high heat resistant segments A. However, these four low heat resistant segments are provided with a SiO ₂ protective layer (oxide film) having a thickness of 0.3 μm and containing 51 mass% silicon and 43 mass% oxygen on the surface of the partition wall. Formed. The remaining 12 low heat resistant segments B are not subjected to oxidation treatment and have no protective layer formed on the surface of the partition wall.

(Comparative Example 5)
A honeycomb filter of Comparative Example 5 was produced in the same manner as Example 1 except that all 16 honeycomb segments were high heat resistant segments.

(Comparative Example 6)
Except for combining a total of 25 honeycomb segments composed of one high heat resistant segment A and 24 low heat resistant segments B so as to be arranged as shown in FIG. A honeycomb filter of Comparative Example 6 was produced. However, the used honeycomb segment had a cross section perpendicular to the cell extending direction and was a square having a side of 39 mm, and the length in the cell extending direction was 152 mm. The honeycomb filter had a diameter of 191 mm and a length of 152 mm. In addition, the ratio of the cross-sectional area of the low heat-resistant segment to the cross-sectional area of all the honeycomb segments (high heat-resistant segment and low heat-resistant segment) in the cross section orthogonal to the cell extending direction of the honeycomb filter was 95%.

(Evaluation)
With respect to the honeycomb filters of Examples 1 to 15 and Comparative Examples 1 to 6 manufactured as described above, each of “PM deposition limit”, “pressure loss detection performance”, and [overall judgment] is performed by the following method. Evaluation was performed. The results are shown in Table 2.

[PM deposition limit]
First, exhaust gas discharged from an inline 6-cylinder common rail direct injection diesel engine having a displacement of 3000 cc was allowed to flow into the honeycomb filter, and 6 g / L of PM was deposited in the honeycomb filter. Next, an oxidation catalyst was installed in the exhaust system of the diesel engine, and a honeycomb filter in which PM was deposited as described above was installed downstream thereof. Next, post-injection was performed with the diesel engine maintained at an engine speed of 2000 rpm and an engine torque of 178 N · m. After the temperature of the exhaust gas flowing into the honeycomb filter reached 600 ° C., the engine was switched to the idle state. The filter was forcibly regenerated. Thereafter, the honeycomb filter was removed, and the presence or absence of cracks in the honeycomb filter was observed with an X-ray CT scanner. This operation was repeated by gradually increasing the amount of PM deposited in the honeycomb filter, and the maximum amount of PM deposited without cracks in the honeycomb filter was examined. Evaluation was based on the honeycomb filter of Comparative Example 5. For example, “−1 g / L” in Table 2 indicates that the maximum PM deposition amount at which cracks do not occur in the honeycomb filter is 1 g / L less than that in Comparative Example 5. A case where the maximum PM deposition amount at which cracks do not occur in the honeycomb filter is equivalent to that in Comparative Example 5 is “A”, which is smaller than Comparative Example 5, but the difference from Comparative Example 5 is 1 g / L or less. The case was designated as “B”, and the case where the difference from Comparative Example 5 exceeded 1 g / L was designated as “C”.

[Pressure loss detection performance]
First, exhaust gas discharged from a 3000 cc, in-line 6-cylinder common rail direct injection diesel engine was allowed to flow into the honeycomb filter, and PM was deposited in the honeycomb filter. The amount of PM deposited was set to an amount larger than the “maximum PM deposition amount at which cracks do not occur in the honeycomb filter” investigated at the PM deposition limit. Next, an oxidation catalyst was installed in the exhaust system of the diesel engine, and a honeycomb filter on which PM was deposited as described above was installed downstream thereof. Next, post-injection was performed with the diesel engine maintained at an engine speed of 2000 rpm and an engine torque of 178 N · m. After the temperature of the exhaust gas flowing into the honeycomb filter reached 600 ° C., the engine was switched to the idle state. The filter was forcibly regenerated. And the change of the pressure loss of the honeycomb filter at the time of this forced regeneration was investigated. At the time of this forced regeneration, if some of the honeycomb segments constituting the honeycomb filter are deformed due to fiber formation, the pressure loss temporarily increases as indicated by the arrows in the graph of FIG. This is because the flow path (cell) is narrowed by deformation due to fiberization. On the other hand, when the honeycomb segment constituting the honeycomb filter is not deformed due to fiber formation, as shown in FIG. 17, the pressure loss gradually decreases as the combustion of PM by the forced regeneration proceeds. . That is, when the honeycomb filter reaches a temperature at which cracks occur, some honeycomb segments undergo deformation due to fiberization, and the occurrence of cracks is detected by examining changes in pressure loss. be able to. A case where a temporary increase in pressure loss as shown in FIG. 16 appears markedly is “A”, and a case where a temporary increase in pressure loss is confirmed is “B”. The case where no temporary increase was confirmed as “C”.

[Comprehensive judgment]
The case where both “PM deposition limit” and “pressure loss detection performance” were “A” was defined as “A”. The case where both “PM deposition limit” and “pressure loss detection performance” are “B” and the case where one of them is “A” and the other is “B” are defined as “B”. The case where at least one of “PM deposition limit” and “pressure loss detection performance” is “C” was defined as “C”.

(Discussion)
As shown in Table 2, in Examples 1 to 15, which are examples of the present invention, the comprehensive judgment was “A” or [B]. In Comparative Examples 1 and 4 in which the honeycomb filter is composed only of the low heat resistance segment, the “PM deposition limit” was “C”, and the heat resistance of the entire honeycomb filter was insufficient. In Comparative Example 3 in which the contents of silicon and oxygen contained in the protective layer of the high heat resistance segment are each less than 40% by mass, the “PM deposition limit” is “C”, and the heat resistance of the entire honeycomb filter Was insufficient. In Comparative Example 5 in which the honeycomb filter is composed of only the high heat resistance segment, the “pressure loss detection performance” is “C”, and it is difficult to detect the occurrence of cracks by examining changes in pressure loss. It was something. In Comparative Example 6 in which the ratio of the cross-sectional area of the low heat resistant segment exceeds 76%, the “PM deposition limit” is “C”, and the heat resistance of the entire honeycomb filter is insufficient. Further, in this Comparative Example 6, the “pressure loss detection performance” was also “C”, and it was difficult to detect the occurrence of cracks by examining changes in pressure loss. Further, in Comparative Example 2 in which the inner segment is a low heat resistant segment and the outer segment is a high heat resistant segment, the “PM deposition limit” is “C”, and the heat resistance of the entire honeycomb filter is insufficient. It was.

  The present invention can be suitably used as a honeycomb filter for removing particulate matter and the like in exhaust gas discharged from an internal combustion engine such as a diesel engine.

1: partition wall, 2: cell, 2a: outlet plugged cell, 2b: inlet plugged cell, 3: plugged portion, 4: honeycomb structure, 5: protective layer, 6: protective layer, 7: honeycomb Segment, 7a: inner segment, 7b: outer segment, 8: bonding material, 9: outer peripheral coating layer, 11: inflow end surface, 12: outflow end surface, 13: circle, 100: honeycomb filter, 200, 300: honeycomb filter, A : High heat resistance segment, B: Low heat resistance segment, G: Center of gravity, O: Center.

Claims (5)

A honeycomb filter composed of a plurality of honeycomb segments,
The honeycomb segment has a porous partition wall that defines a plurality of cells serving as fluid flow paths extending from an inflow end surface that is an end surface on the fluid inflow side to an outflow end surface that is an end surface on the fluid outflow side. A structure portion, and a plugging portion disposed at one end of either the inflow end face side or the outflow end face side of the plurality of cells,
The plurality of honeycomb segments are combined in a direction perpendicular to the cell extending direction and joined and integrated,
The honeycomb structure part is composed of an aggregate made of silicon carbide, and a binder that bonds the aggregates together,
In the cross section orthogonal to the cell extending direction of the honeycomb filter, the honeycomb segment including at least a part thereof in a circle having a diameter of 3.6 cm centered on the center of gravity of the cross section is defined as an inner segment, and the other segments The honeycomb segment is the outer segment,
At least one of the outer segments has a protective layer having a thickness of 0.3 μm or less on the surface of the partition wall or is a low heat resistant segment having no protective layer,
Among the inner segment and the outer segment, those other than the low heat resistant segment are high heat resistant segments having a protective layer having a thickness of 0.5 to 7.3 μm on the surface of the partition wall,
The protective layer is a layer containing 40% by mass or more of silicon and 40% by mass or more of oxygen,
A honeycomb filter in which a ratio of a cross-sectional area of the low heat-resistant segment to a cross-sectional area of all the honeycomb segments in a cross section perpendicular to the cell extending direction of the honeycomb filter is 16 to 76%.   The honeycomb filter according to claim 1, wherein a thickness of the protective layer of the high heat resistant segment is 1.0 to 6.0 µm.   The honeycomb according to claim 1 or 2, wherein a ratio of a cross-sectional area of the low heat-resistant segment to a cross-sectional area of all the honeycomb segments in a cross-section orthogonal to the cell extending direction of the honeycomb filter is 32 to 66%. filter.   The honeycomb filter according to any one of claims 1 to 3, wherein the binder contains silicon or cordierite.   The honeycomb filter according to any one of claims 1 to 4, wherein a catalyst is supported on the honeycomb structure part.

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