JP6948273B2 - Honeycomb filter - Google Patents

Description

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

Exhaust gas emitted 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, which causes environmental pollution. Therefore, the exhaust system of a diesel engine or the like is generally equipped with a filter for removing (collecting) PM.

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 sealing portion. The honeycomb structure has a porous partition wall that partitions a plurality of cells extending from the inflow end face, which is the end face on the side where the fluid flows in, to the outflow end face, which is the end face on the side where the fluid flows out. A honeycomb filter can be obtained by disposing a mesh sealing portion that seals one end of each cell on any end surface 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 sealed at the outflow end face. The exhaust gas then passes through the porous partition and moves into the cell whose ends are sealed at the inflow end face. Then, when the exhaust gas permeates the porous partition wall, the partition wall becomes a filtration layer, and PM in the exhaust gas is captured by the partition wall and deposited on the partition wall. The exhaust gas from which PM has been removed in this way then flows out from the outflow end face.

By the way, in order to use the honeycomb filter continuously 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 the PM accumulated over time on the partition wall of the honeycomb filter and return the filter performance to the initial state, it is necessary to burn and remove the PM accumulated on the partition wall.

The temperature of the honeycomb filter during regeneration is usually about 800 to 900 ° C. However, if PM combustion is insufficient during the previous regeneration and PM is excessively deposited in the filter, the temperature of the honeycomb filter rises to around 1300 ° C., which is the heat resistance limit temperature, and the honeycomb filter Cracks may occur in the honeycomb.

If the honeycomb filter in which such cracks are generated is continued to be used as it is, PM leaks from the cracks and pollutes the environment. Therefore, a technique capable of detecting the occurrence of cracks is required.

As a technique for detecting cracks in the honeycomb filter, it is conceivable to arrange a device capable of detecting PM leaked from the cracks in the honeycomb filter on the downstream side of the honeycomb filter. Conventionally, as a device capable of detecting PM, a PN measuring device for measuring the number of PM particles (PN: Particle Number) and a PM sensor for measuring the weight of PM are known.

Japanese Unexamined Patent Publication No. 57-7215 Japanese Unexamined Patent Publication No. 2000-279729

However, since the PN measuring device is very expensive and large enough to be difficult to be mounted on a commercially available vehicle, it is not realistic to detect the occurrence of cracks by using the PN measuring device. Further, when the cracks generated in the honeycomb filter are fine, it is difficult for the PM sensor to detect the occurrence of the cracks. That is, since PM that can leak 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 that leaks from the crack.

It is also possible to detect cracks in the honeycomb filter by changing the pressure loss of the honeycomb filter, but if the cracks generated in the honeycomb filter are fine as described above, the change in 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, the present invention is to provide a honeycomb filter capable of inexpensively and easily detecting the occurrence of cracks when cracks are generated due to excessive temperature rise during regeneration of the honeycomb filter.

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

[1] A honeycomb filter composed of a plurality of honeycomb segments.
The honeycomb segment is a honeycomb having a porous partition wall that partitions a plurality of cells serving as a flow path of the fluid extending from the inflow end face, which is the end face on the fluid inflow side, to the outflow end face, which is the end face on the fluid outflow side. It is provided with a structural portion and a mesh sealing portion disposed at either end of the inflow end face side or the outflow end face side of the plurality of cells.
The honeycomb filter is formed by combining a plurality of honeycomb segments in a direction perpendicular to the extending direction of the cell and joining and integrating them.
The honeycomb structure is composed of an aggregate made of silicon carbide and a binder that binds the aggregates together.
In a cross section orthogonal to the extending direction of the cell of the honeycomb filter, the honeycomb segment having 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 said. The honeycomb segment is the outer segment
At least one of the outer segments is a low heat resistant segment having a protective layer having a thickness of 0.3 μm or less or having no protective layer on the surface of the partition wall.
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 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 extending direction of the cell of the honeycomb filter is 16 to 76%.

[2] The honeycomb filter according to [1], wherein the protective layer of the highly 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 orthogonal to the extending direction of the cell of the honeycomb filter is 32 to 66% [1] or [2]. ] The honeycomb filter described in.

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

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

In the honeycomb filter of the present invention, when the maximum temperature in the filter reaches a temperature at which cracks occur, some of the honeycomb segments constituting the honeycomb filter are fiberized by active oxidation and deformed. Then, due to this deformation, large cracks are generated in the honeycomb filter so that even PM having a relatively large particle size and a heavy weight can pass through. Therefore, in the honeycomb filter of the present invention, it is easy to detect the PM leaked from the crack by the PM sensor and the change in the pressure loss due to the deformation, and it is not necessary to use an expensive and large PN measuring device. , The occurrence of cracks can be easily detected.

It is a perspective view which shows typically one Embodiment of the honeycomb filter of this invention. It is explanatory drawing which shows the inner segment and the outer segment in the cross section orthogonal to the extending direction of the cell of a honeycomb filter. It is explanatory drawing which shows the inner segment and the outer segment in the cross section orthogonal to the extending direction of the cell of a honeycomb filter. It is one embodiment of the low heat resistance segment, and is sectional drawing which shows typically the cross section parallel to the extending direction of a cell. Another embodiment of the low heat resistance segment is a cross-sectional view schematically showing a cross section parallel to the extending direction of the cell. FIG. 5 is a cross-sectional view schematically showing a cross section parallel to the extending direction of the cell, which is one embodiment of the high heat resistance segment. It is explanatory drawing which shows the example of the combination of the high heat resistance segment and the low heat resistance segment in the honeycomb filter of this invention. It is explanatory drawing which shows the example of the combination of the high heat resistance segment and the low heat resistance segment in the honeycomb filter of this invention. It is explanatory drawing which shows the example of the combination of the high heat resistance segment and the low heat resistance segment in the honeycomb filter of this invention. It is explanatory drawing which shows the example of the combination of the high heat resistance segment and the low heat resistance segment in the honeycomb filter of this invention. It is explanatory drawing which shows the example of the combination of the high heat resistance segment and the low heat resistance segment in the honeycomb filter of this invention. It is explanatory drawing which shows the example of the combination of the high heat resistance segment and the low heat resistance segment in the honeycomb filter of this invention. It is explanatory drawing which shows the example of the combination of the high heat resistance segment and the low heat resistance segment in the honeycomb filter of this invention. It is explanatory drawing which shows the example of the combination of the high heat resistance segment and the low heat resistance segment in the honeycomb filter which does not satisfy the requirement of this invention. It is explanatory drawing which shows the example of the combination of the high heat resistance segment and the low heat resistance segment in the honeycomb filter which does not satisfy the requirement of this invention. It is a graph which shows the change of the pressure loss when the honeycomb filter is deformed by fiberification when the honeycomb filter is regenerated with the engine in an idle state. It is a graph which shows the change of the pressure loss when the honeycomb filter is regenerated with the engine in an idle state, and the honeycomb filter is not deformed by fiber formation.

Hereinafter, the present invention will be described based on specific embodiments, but the present invention will not be construed as being limited to those embodiments, and will be ordinary to those skilled in the art without departing from the spirit of the present invention. Based on the knowledge, the design can be changed or improved as appropriate.

(1) Honeycomb filter:
FIG. 1 is a perspective view schematically showing an embodiment of the honeycomb filter of the present invention. The honeycomb filter 100, which is one embodiment of the honeycomb filter of the present invention, is composed of a plurality of honeycomb segments 7. The honeycomb segment 7 includes a honeycomb structure portion 4 and a sealing portion 3. The honeycomb structure portion 4 partitions a plurality of cells 2 serving as a flow path of the fluid extending from the inflow end face 11 which is the end face on the side where the fluid such as exhaust gas flows in to the outflow end face 12 which is the end face on the side where the fluid flows out. It has a porous partition wall 1. The sealing portion 3 is arranged at one end of the plurality of cells 2 on either 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 cell 2 and joining and integrating them via a joining material 8.

A part of the plurality of honeycomb segments 7 constituting the honeycomb filter 100 is the inner segment 7a, and the remaining part is the outer segment 7b. 2 and 3 are explanatory views showing an inner segment 7a and an outer segment 7b in a cross section orthogonal to the extending direction of the cells of the honeycomb filter 100. In these figures, the drawing of the partition wall and the sealing portion of the honeycomb segment 7 is omitted.

In the present invention, as shown in FIGS. 2 and 3, in a cross section orthogonal to the extending direction of the cells of the honeycomb filter 100, at least in a circle 13 having a diameter of 3.6 cm centered on the center of gravity G of the cross section. The honeycomb segment 7 including a part thereof is referred to as an inner segment 7a. Further, the honeycomb segment other than the inner segment 7a is referred to as the outer segment 7b. The "center of gravity" referred to here is the center of gravity of a figure drawn by the outer peripheral edge of the honeycomb filter 100 in a cross section orthogonal to the extending direction of the cell 2 of the honeycomb filter 100. In the example of FIG. 2, of the 16 honeycomb segments 7 constituting the honeycomb filter 100, 4 honeycomb segments 7 having at least a part thereof in the circle 13 are inner segments 7a, and the other 12 honeycomb segments 7 are included. Honeycomb segment 7 is an outer segment 7b. Further, in the example of FIG. 3, of the 25 honeycomb segments 7 constituting the honeycomb filter 100, one honeycomb segment 7 in which at least a part thereof is included in the circle 13 is the inner segment 7a, and the other ones. The 24 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. Further, among 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 resistance 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. The highly 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 extending direction of the cell, which is one embodiment of the low heat resistance segment. FIG. 5 is another embodiment of the low heat resistance segment, which is a cross-sectional view schematically showing a cross section parallel to the extending direction of the cell. FIG. 6 is a cross-sectional view schematically showing a cross section parallel to the extending direction of the cell, which is one embodiment of the high heat resistant segment.

In one embodiment of the low heat resistance 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, a 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. Further, in one embodiment of the high heat resistance 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 / absence and thickness of such a protective layer may be the same in the low heat resistance segment B and the high heat resistance segment A. That is, in both the low heat resistance segment B and the high heat resistance segment A, the honeycomb structure portion 4 has a porous partition wall 1 that partitions a plurality of cells 2 extending from the inflow end face 11 to the outflow end face 12. Some of the cells in the plurality of cells 2 are inlet sealing cells 2b whose ends are sealed by the sealing portion 3 on the inflow end surface 11 side of the honeycomb structure portion 4. Further, the remaining cells in the plurality of cells 2 are outlet eye-sealing cells 2a whose ends are eye-sealed by the eye-sealing portion 3 on the outflow end surface 12 side of the honeycomb structure portion 4. The outlet sealing cell 2a and the inlet sealing cell 2b are alternately arranged so as to be adjacent to each other with the partition wall 1 in between.

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 oxidative decomposition reaction of silicon carbide that occurs when a silicon carbide material is exposed to a high temperature in a low oxygen atmosphere. Specifically, as shown in the following formula (1), silicon monoxide (SiO) gas is generated from silicon carbide (SiC). The SiO gas generated by this active oxidation is then combined with oxygen (O ₂ ) in the atmosphere to precipitate a fibrous substance (fiber) composed of silicon dioxide (SiO _{2), as shown in the following formula (2).} .. Such a phenomenon is called "fiber formation".
Equation (1): SiC (solid) + O ₂ (gas) → SiO (gas) + CO (gas)
Equation (2): SiO (gas) + 1 / 2O ₂ (gas) → SiO ₂ (solid)

The surface of the partition wall 1 does not have a protective layer, or even if the protective layer 6 is provided, the low heat resistance segment B having a thickness of 0.3 μm or less is similar to that at the time of regeneration of the honeycomb filter 100. Silicon carbide, which is an aggregate, is actively oxidized at about 1200 ° C. in a low oxygen atmosphere. Then, when fiber formation occurs due to this active oxidation, the low heat resistant segment B is deformed, and along with this, large cracks are generated. Further, in the initial stage of fiber formation, the flow path (cell) is narrowed due to the deformation of the low heat resistant segment B, and the pressure loss temporarily increases.

On the other hand, in the highly 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, 1300 is used even in a low oxygen atmosphere such as when the honeycomb filter 100 is regenerated. Active oxidation does not occur up to about ° C, and fiber formation 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 fiber formation occurs in the low heat resistant segment B.

7 to 13 are explanatory views showing an example of a combination 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 figures, the drawing of the partition wall and the sealing portion of the honeycomb segment is omitted. Further, in these figures, the honeycomb segment surrounded by the dotted line is the inner segment, and the other honeycomb segments are the outer segments.

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

Further, in the example of FIG. 11, of the 25 honeycomb segments constituting the honeycomb filter 100, one inner segment and four outer segments are high heat resistant segments A, and 20 outer segments are low. It is a heat resistant segment B. In the example of FIG. 12, of the 25 honeycomb segments constituting the honeycomb filter 100, one inner segment and eight outer segments are high heat resistant segments A, and 16 outer segments have 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 high heat resistant segments A, and nine outer segments have low heat resistance. Segment B.

According to the study by the present inventors, when the temperature near the center (near where the inner segment is arranged), which is the highest temperature during regeneration of the honeycomb filter 100, reaches about 1300 ° C., it becomes the lowest temperature. It reaches about 1200 ° C even near the outer circumference. Therefore, when the high heat-resistant segment A reaches the temperature at which cracks occur (about 1300 ° C.), the low heat-resistant segment B reaches the temperature at which active oxidation occurs (about 1200 ° C.), and the fiber Deformation due to conversion has begun. 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 the temperature at which cracks occur, the outer segment (low heat resistant segment B) ) Will be deformed. Then, due to the deformation due to this fiber formation, large cracks are generated in the honeycomb filter 100 so that even a heavy PM having a relatively large particle size can pass through. Further, in the initial stage of fiber formation, the flow path (cell) is narrowed due to the deformation of the low heat resistant segment B, and the pressure loss temporarily increases.

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

The arrangement and number of the low heat resistance segment B and the high heat resistance segment A in the honeycomb filter 100 are not limited to the examples of FIGS. 7 to 13. 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 orthogonal 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%, it may be difficult to detect the occurrence of cracks. On the other hand, if this ratio exceeds 76%, the amount of PM that can be burned without causing cracks during regeneration may become 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 a high heat resistant segment A, and all 24 outer segments are low heat resistant segments B. The ratio exceeds 76%. Further, FIG. 15 is also an explanatory diagram showing an example of a combination of a low heat resistance segment and a high heat resistance segment in a honeycomb filter that does not satisfy the requirements of the present invention. In the example of FIG. 15, of the 16 honeycomb segments constituting the honeycomb filter 300, 4 inner segments are low heat resistant segments B and 12 outer segments are high heat resistant segments A.

The thickness of the protective layer 5 formed on the surface of the partition wall 1 of the highly heat-resistant segment A as shown in FIG. 6 is 0.5 to 7.3 μm, 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 highly heat-resistant segment A cannot be sufficiently suppressed, and the amount of PM that can be burned without causing cracks during regeneration is small. It may be too much. On the other hand, when the thickness of this protective layer exceeds 7.3 μm, the thermal expansion coefficient increases, so that the thermal stress generated during regeneration increases and cracks are likely to occur, and combustion is performed without generating cracks during regeneration. The amount of PM that can be produced may be too small.

The thickness of the low heat resistant segment B as shown in FIG. 5 is such that the protective layer is not formed on the surface of the partition wall 1, or even if the protective layer 6 as shown in FIG. 4 is formed, for example. It is 0.3 μm or less. If a 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 high heat resistant segment A has low heat resistance even if it reaches a temperature at which cracks occur. The sex segment B may not be deformed due to fiber formation and cracks associated therewith may not occur.

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 highly heat-resistant segment A so as to have a thickness of 0.5 to 7.3 μm, the height is increased. The 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 a protective layer having the above-mentioned thickness is formed on the surface of the partition wall 1 of the high heat resistance segment A, the heat resistance is high. The active oxidation of 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 50% by mass or more of silicon and 43% by mass or more of oxygen, and 53% by mass. It is more preferable to contain the above silicon and 46% by mass or more of oxygen.

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

The presence or absence of the protective layer and the measurement of the thickness of the protective layer can be performed using FE-EPMA (field emission electron probe microanalyzer). Specifically, first, in FE-EPMA, 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 wall of the honeycomb segment. Check for the presence of. Next, from the partition wall where it was confirmed that the protective layer was formed, five visual fields of 100 μm in length × 100 μm in width were randomly extracted. Then, for each field of view, the protective layer covering the SiC particles (aggregate) was randomly extracted at 10 points and the thickness was measured, and the average value of the total thickness of 50 points was taken as the thickness of the protective layer. do.

The honeycomb structure portion 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 to each other. The binder preferably contains silicon (Si) or cordierite. Since the binder contains silicon, high thermal conductivity can be obtained and the temperature during filter regeneration can be suppressed. Further, since the binder contains cordierite, the coefficient of thermal expansion is lowered and cracks are less likely to occur.

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

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

The porosity of the partition wall 1 is preferably 25 to 80%, more preferably 30 to 76%, and particularly preferably 35 to 72%. If 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 in an exhaust system such as a diesel engine, the output of the engine may decrease. 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 porosity meter.

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. If 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 in an exhaust system such as a diesel engine, the output of the engine may decrease. Further, if the average pore diameter of the partition wall 1 exceeds 100 μm, sufficient strength may not be obtained. The "average pore diameter" referred to here 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. If the cell density of the honeycomb structure portion 4 ^{is less than 15 cells / cm 2} , the strength of the honeycomb filter 100 and the effective filtration area may be insufficient. Further, when the cell density of the honeycomb structure portion 4 ^{exceeds 650 cells / cm 2} , the distance between the partition walls 1 surrounding the cell 2 becomes short, so that the flow path (cell 2) may be clogged with PM.

The cell shape of the honeycomb structure portion 4 (the shape of the cell 2 in the cross section orthogonal to the extending direction of the cell 2) is not particularly limited. Preferred cell shapes include polygons such as triangles, quadrangles, pentagons, hexagons, and octagons, circles, ellipses, and combinations thereof. Among the quadrangles, a square or a rectangle is preferable.

The overall shape of the honeycomb filter 100 is not particularly limited. Preferred overall shapes of the honeycomb filter 100 include a columnar shape, a columnar shape having an elliptical end face, a polygonal columnar shape having a square end face, a rectangle, a triangle, a pentagon, a hexagon, an octagon, and the like. The shape of the honeycomb filter 100 shown in FIG. 1 is cylindrical.

The 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, 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 cracked. 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 and purify harmful components contained in the exhaust gas. Examples of the catalyst include an oxidation catalyst, a three-way catalyst, a reduction catalyst and the like.

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 amount of the catalyst supported 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 amount (g / L) referred to here is the amount (g) of the catalyst supported per unit volume (1L) of the honeycomb structure portion.

(2) Honeycomb filter manufacturing method:
Hereinafter, an example of the method for manufacturing the honeycomb filter of the present invention will be described. First, a molding raw material containing a ceramic raw material is prepared. As the ceramic raw material, one composed of silicon carbide as an aggregate and silicon or a cordierite-forming raw material as a binder is preferable. The cordierite-forming raw material is a raw material that becomes cordierite by firing. 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 formulated so as to have a chemical composition within the range of mass%.

The molding 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-forming material, 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 materials has a hardness that makes it easy to mold. The specific content of the dispersion medium is preferably 20 to 80% by mass with respect to the entire molding raw material.

As the 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 molding raw material.

Examples of the organic binder include methyl cellulose, hydroxypropoxyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, polyvinyl alcohol and the like. 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 molding 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, or 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 entire molding raw material.

The pore-forming material 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 content of the pore-forming material is preferably 10% by mass or less with respect to the entire molding raw material.

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

Next, the obtained clay is molded to form a honeycomb molded body. The honeycomb molded body is a molded body having a partition wall for partitioning a plurality of cells serving as a fluid flow path. The method for forming the honeycomb molded body by molding the clay 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 extrusion molding using a base corresponding to a desired cell shape, partition wall thickness, etc. can be mentioned as a preferable example. As the material of the base, a cemented carbide that is hard to wear is preferable.

The honeycomb molded product thus obtained is dried and then fired. Examples of the drying method include hot air drying, microwave drying, dielectric drying, vacuum drying, vacuum drying, freeze drying and the like. Above all, it is preferable to perform dielectric drying, microwave drying or hot air drying alone or in combination.

The dried honeycomb molded body (honeycomb dried body) is fired to produce a honeycomb structure. Prior to this firing (main firing), it is preferable to perform calcining (solvent degreasing) in order to remove the binder and the like contained in the honeycomb molded body. The conditions for calcining are not particularly limited, and any conditions may be sufficient as long as the organic substances (organic binder, surfactant, pore-forming material, etc.) contained in the honeycomb molded 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-forming material is about 200 to 800 ° C. Therefore, as a condition for calcining, it is preferable to heat in an oxidizing atmosphere at about 200 to 1000 ° C. for about 3 to 100 hours.

The firing (main firing) of the honeycomb molded body is performed in order to obtain a predetermined strength by sintering and densifying the molding raw material constituting the temporarily baked honeycomb molded body. Since the firing conditions (temperature, time, atmosphere, etc.) differ depending on the type of molding raw material, appropriate conditions may be selected according to the type.

Next, a mesh sealing portion is formed on the honeycomb structure portion. The mesh sealing portion is formed so that the end portion of the outlet mesh sealing cell is sealed on the outflow end face side of the honeycomb structure, and the inlet sealing cell is formed so that the end face is sealed. On the side, it is formed so that the end is sealed. A conventionally known method can be used for forming the mesh sealing portion. As an example of a specific method, first, a sheet is attached to the end face of the honeycomb structure portion produced by the above method. Next, a hole is made in the sheet at a position corresponding to the cell in which the eye seal portion is to be formed. Next, with this sheet still attached, the end face of the honeycomb structure is dipped in the slurry for sealing, which is a slurry of the material for forming the sealing portion, and the sealing is performed through the holes made in the sheet. The opening end of the cell to be stopped is filled with the sealing slurry.

By drying the sealing slurry filled in the cell and then firing and curing the slurry, a honeycomb segment having a honeycomb structure portion and a sealing portion can be obtained. It is preferable to use the same material as the material for forming the honeycomb structure portion as the material for forming the sealing portion. The mesh sealing portion may be formed at any stage after the honeycomb molded body is dried, calcined, or fired (main fired).

Among the honeycomb segments thus obtained, 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 of heating the honeycomb segment in an oxygen atmosphere (for example, an oxygen concentration of 15 to 20% by mass) at 900 to 1400 ° C. for about 5 to 20 hours. By oxidizing the honeycomb segment by such a method, a part of silicon carbide which is an aggregate is oxidized, and silica containing 40% by mass or more of silicon and 40% by mass or more of oxygen is contained on the surface of the partition wall. A (SiO ₂ ) quality protective layer (oxide film) is formed.

Among the honeycomb segments obtained as described above, those having a low heat resistance segment basically do not require a protective layer, and therefore do not need to be subjected to an oxidation treatment. However, even if the segment has low heat resistance, a protective layer may be formed on the surface of the partition wall as long as the thickness is less than 0.3 μm. The protective layer having a thickness of less than 0.3 μm may be formed in the process of firing (main firing) of the honeycomb molded body described above without any special oxidation treatment. When the protective layer having a thickness of less than 0.3 μm is formed by the oxidation treatment, the oxygen concentration in the heating atmosphere is lowered and the heating time is shortened as compared with the case where the protective layer of the highly heat-resistant segment is formed. It is preferable to adjust the thickness of the protective layer formed by such a method.

Next, a slurry-like joining material is applied to each side surface of the high heat-resistant segment and the low heat-resistant segment, and the high-heat-resistant segment and the low-heat-resistant segment are joined so that the side surfaces are joined by the joining material. Combine with. At this time, at least one of the outer segments is set to be a low heat resistant segment. Further, the high heat-resistant segment is such 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 extending direction of the cell of the finally obtained honeycomb filter is 16 to 76%. And adjust 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 joined and integrated via the bonding material. The resulting honeycomb segment joint is obtained.

As the bonding material, for example, an inorganic raw material such as inorganic fiber, colloidal silica, clay, or ceramic particles is kneaded with an additive such as an organic binder, an effervescent resin, or a dispersant and water to form a slurry. , Can be preferably used. The method of applying the bonding material to each side surface of the high heat resistance segment and the low heat resistance segment is not particularly limited, and a method such as brush coating can be used.

The honeycomb segment joint can be used as a honeycomb filter as it is, but if necessary, the outer peripheral portion thereof may be ground to form 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 honeycomb segment joint body after grinding. As the outer peripheral coating material, an inorganic raw material binder such as inorganic fiber, colloidal silica, clay, ceramic particles, an additive such as a foamed resin and a dispersant, and water are added and kneaded to form a slurry, which is preferably used. can. The method of applying the outer peripheral coating material to the processed surface of the honeycomb joint 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 honeycomb segment joint body after the grinding process on the potter's wheel can be mentioned.

(3) Catalyst supporting method:
Next, an example of a method of supporting the catalyst on the honeycomb structure portion of the honeycomb filter manufactured as described above will be described. First, a catalyst slurry containing a catalyst to be supported is prepared. This catalyst slurry is coated on the partition wall of the honeycomb structure. The coating method is not particularly limited. For example, a method of sucking from the other end face of the honeycomb structure portion (suction method) in a state where one end face of the honeycomb structure portion is immersed in the catalyst slurry can be mentioned as a preferable coating method. In this way, after the catalyst slurry is coated on the partition wall of the honeycomb structure portion, the catalyst slurry is dried. Further, the dried catalyst slurry may be calcined. In this way, a honeycomb filter in which an oxidation catalyst is supported on the honeycomb structure can be obtained.

Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to these examples.

(Example 1)
Silicon carbide (SiC) powder and metallic 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-absorbent resin as a pore-forming material were added, and water was added as a dispersion medium to prepare a molding raw material, and this molding raw material was kneaded with a vacuum clay kneader. The 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 amount of the pore-forming material added 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 clay was extruded using a base having a predetermined shape to obtain a honeycomb molded body having a square columnar shape as a whole. The honeycomb molded product thus obtained was dried by a microwave dryer and then further dried by a hot air dryer to obtain a honeycomb dried product.

Next, a sealing portion was formed at one end of a predetermined cell of the dried honeycomb body and at the other end of the remaining cell. The formation of the eye-sealing portion is such that both end faces of the dried honeycomb are checked in a checkered pattern by a cell in which the eye-sealing portion is formed at the end and a cell in which the eye-sealing portion is not formed at the end. I went like that. As a method for forming the eye-sealing portion, first, a sheet was attached to the end face of the dried honeycomb body, and a hole was made in the sheet at a position corresponding to the cell in which the eye-sealing portion was to be formed. Subsequently, with this sheet still attached, the end face of the dried honeycomb body is immersed in the slurry for sealing, which is a slurry of the material for forming the sealing portion, and the sealing is performed through the holes made in the sheet. The end of the cell to be stopped was filled with a slurry for sealing. As the material for forming the sealing portion, the same material as the molding raw material was used.

In this way, the slurry for sealing the eyes filled in the end of the cell was dried, and then the dried honeycomb was calcined (defatted) 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 cross section of 36 mm on a side orthogonal to the extending direction of the cell, and had a length of 152 mm in the extending direction of the cell. 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 binding the aggregates to each other.

A part of the honeycomb segments among the plurality of honeycomb segments thus obtained is subjected to an oxidation treatment, and the surface of the partition wall is 1.5 μm thick, and has 53% by mass of silicon and 46% by mass of oxygen. SiO ₂ quality protective layer, including bets was formed (oxide film). The oxidation treatment was carried out by heating the honeycomb segment at 1300 ° C. for 5 hours in an oxygen atmosphere having an oxygen concentration of 20% by mass. The honeycomb segment subjected to the oxidation treatment in this way was designated as a high heat resistant segment, and the honeycomb segment not subjected to the oxidation treatment was designated as a low heat resistant segment.

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 coated with the bonding material in this way are combined so as to have the arrangement shown in FIG. A honeycomb segment laminate was produced. This honeycomb segment laminate was dried at 120 ° C. for 2 hours to obtain a honeycomb segment joint having a square columnar shape as a whole.

Next, the outer circumference of the honeycomb segment joint was ground so that the overall shape would be cylindrical. After the grinding process, an outer peripheral coating material having the same composition as the bonding material was applied to the processed surface to a thickness of 1 mm, and dried and cured at 700 ° C. for 2 hours to form an outer peripheral coating layer.

The honeycomb filter of Example 1 thus produced had a diameter of 144 mm and a length of 152 mm. The thickness of the partition wall was 320 μm, and the porosity of the partition wall 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 orthogonal to the extending direction of the cells of the honeycomb filter was 66%.

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

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

(Example 9)
_{As the low heat-resistant segment, one having a thickness of 0.3 μm and a SiO 2} quality protective layer (oxide film) containing 50% by mass of silicon and 43% by mass of oxygen formed on the surface of the partition wall was used. A honeycomb filter of Example 9 was produced in the same manner as in Example 1 except for the above.

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

(Example 11)
Example 10 except that the thickness of the protective layer of the highly 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 of each honeycomb segment. In the same manner as in the above, the honeycomb filter of Example 11 was produced. The catalyst is supported by forming a coat layer of a catalyst slurry containing platinum (Pt) and rhodium (Rh) at a ratio of 5: 1 on the surface of the partition wall of the honeycomb segment bonded body by a suction method, and then heating the catalyst. This was done by drying. The total amount of precious metals (Pt, Rh) supported per liter of the volume of the honeycomb filter was 15 g.

(Example 12)
A total of 16 honeycomb segments consisting of 13 high heat resistant segments A and 3 low heat resistant segments B were combined in the same manner as in Example 2 except that they were combined so as to have the arrangement shown in FIG. The 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 orthogonal to the extending direction of the cells of the honeycomb filter was 16%.

(Example 13)
A total of 16 honeycomb segments consisting of 10 high heat resistant segments A and 6 low heat resistant segments B were combined in the same manner as in Example 1 except that they were combined so as to have the arrangement shown in FIG. The 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 orthogonal to the extending direction of the cells of the honeycomb filter was 32%.

(Example 14)
A total of 25 honeycomb segments consisting of 5 high heat resistant segments A and 20 low heat resistant segments B were combined in the same manner as in Example 1 except that they were combined so as to have the arrangement shown in FIG. The honeycomb filter of Example 14 was produced. However, the honeycomb segment used was a square having a cross section of 39 mm on a side orthogonal to the extending direction of the cell, and had a length of 152 mm in the extending direction of the cell. 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 orthogonal to the extending direction of the cells of the honeycomb filter was 76%.

(Example 15)
A total of 25 honeycomb segments consisting of 9 high heat resistant segments A and 16 low heat resistant segments B were combined in the same manner as in Example 1 except that they were combined so as to have the arrangement shown in FIG. The honeycomb filter of Example 15 was produced. However, the honeycomb segment used was a square having a cross section of 39 mm on a side orthogonal to the extending direction of the cell, and had a length of 152 mm in the extending direction of the cell. 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 orthogonal to the extending direction of the cells 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 16 honeycomb segments were low heat resistant segments.

(Comparative Example 2)
A total of 16 honeycomb segments consisting of 12 high heat resistant segments A and 4 low heat resistant segments B were combined in the same manner as in Example 1 except that they were combined so as to have the arrangement shown in FIG. The 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)
Honeycomb of Comparative Example 3 in the same manner as in Example 1 except that the content of silicon and oxygen in the protective layer of the highly heat-resistant segment was changed to the value shown in Table 1 by adjusting the conditions of the oxidation treatment. A filter was prepared.

(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 were used instead of the four high heat resistant segments A. However, this four low heat resistance segment, to the surface of the partition wall, in the 0.3μm thick, SiO ₂ quality protective layer containing a 51% by weight of silicon and 43 wt% oxygen (oxide film) It is formed. The remaining 12 low heat-resistant segments B are not oxidized and have no protective layer formed on the surface of the partition wall.

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

(Comparative Example 6)
A total of 25 honeycomb segments consisting of one high heat resistant segment A and 24 low heat resistant segments B were combined in the same manner as in Example 1 except that they were combined so as to have the arrangement shown in FIG. The honeycomb filter of Comparative Example 6 was produced. However, the honeycomb segment used was a square having a cross section of 39 mm on a side orthogonal to the extending direction of the cell, and had a length of 152 mm in the extending direction of the cell. 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 orthogonal to the extending direction of the cells of the honeycomb filter was 95%.

(evaluation)
With respect to the honeycomb filters of Examples 1 to 15 and Comparative Examples 1 to 6 produced as described above, each of "PM deposition limit", "pressure loss detection performance" and [comprehensive judgment] was performed by the methods shown below. Evaluation was performed. The results are shown in Table 2.

[PM deposition limit]
First, the exhaust gas discharged from the in-line 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 on which PM was deposited as described above was installed downstream thereof. Next, post-injection is performed with the diesel engine maintained at an engine speed of 2000 rpm and an engine torque of 178 Nm. After the temperature of the exhaust gas flowing into the honeycomb filter reaches 600 ° C., the diesel engine is switched to an idle state to perform honeycomb. Forced regeneration of the filter was performed. Then, the honeycomb filter was removed, and the presence or absence of cracks in the honeycomb filter was observed with an X-ray CT scanner. The amount of PM deposited in the honeycomb filter was gradually increased, and this operation was repeated to investigate the maximum amount of PM deposited in the honeycomb filter without cracking. The evaluation was based on the honeycomb filter of Comparative Example 5. For example, "-1 g / L" in Table 2 indicates that the maximum amount of PM deposited without cracking in the honeycomb filter was 1 g / L less than that of Comparative Example 5. The case where the maximum amount of PM deposited without cracking in the honeycomb filter was the same as that of Comparative Example 5 was regarded as "A", which was smaller than that of Comparative Example 5, but the difference from Comparative Example 5 was 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, the exhaust gas discharged from the in-line 6-cylinder common rail direct-injection diesel engine having a displacement of 3000 cc was allowed to flow into the honeycomb filter, and PM was deposited in the honeycomb filter. The amount of PM deposited was set to be larger than the "maximum amount of PM deposited without cracking in the honeycomb filter" examined at the above 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 is performed with the diesel engine maintained at an engine speed of 2000 rpm and an engine torque of 178 Nm. After the temperature of the exhaust gas flowing into the honeycomb filter reaches 600 ° C., the diesel engine is switched to an idle state to perform honeycomb. Forced regeneration of the filter was performed. Then, the change in the pressure loss of the honeycomb filter during this forced regeneration was investigated. During 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 shown by the arrows in the graph of FIG. This is because the flow path (cell) is narrowed due to the deformation due to fiber formation. On the other hand, when the honeycomb segments constituting the honeycomb filter are not deformed due to fiber formation, as shown in FIG. 17, the pressure loss gradually decreases as the combustion of PM due to forced regeneration progresses. .. That is, when the honeycomb filter reaches a temperature at which cracks occur, some of the honeycomb segments are deformed due to fiber formation. The honeycomb filter detects the occurrence of cracks by examining the change in pressure loss. be able to. A case where a temporary increase in pressure loss as shown in FIG. 16 appears remarkably is defined as "A", and a case where a temporary increase in pressure loss can be confirmed, although not remarkably, is defined as "B". The case where a temporary increase in the pressure was not confirmed was defined 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 the "PM deposition limit" and the "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 the "PM deposition limit" and the "pressure loss detection performance" was "C" was defined as "C".

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

INDUSTRIAL APPLICABILITY 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, 2: Cell, 2a: Outlet sealing cell, 2b: Inlet sealing cell, 3: Eye sealing, 4: Honeycomb structure, 5: Protective layer, 6: Protective layer, 7: Honeycomb Segment, 7a: Inner segment, 7b: Outer segment, 8: Bonding material, 9: Outer coat layer, 11: Inflow end face, 12: Outflow end face, 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 is a honeycomb having a porous partition wall that partitions a plurality of cells serving as a flow path of the fluid extending from the inflow end face, which is the end face on the fluid inflow side, to the outflow end face, which is the end face on the fluid outflow side. It is provided with a structural portion and a mesh sealing portion disposed at either end of 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 extending direction of the cell, and are joined and integrated.
The honeycomb structure is composed of an aggregate made of silicon carbide and a binder that binds the aggregates together.
In a cross section orthogonal to the extending direction of the cell of the honeycomb filter, the honeycomb segment having 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 said. The honeycomb segment is the outer segment
At least one of the outer segments is a low heat resistant segment having a protective layer having a thickness of 0.3 μm or less or having no protective layer on the surface of the partition wall.
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 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 extending direction of the cell of the honeycomb filter is 16 to 76%. The honeycomb filter according to claim 1, wherein the protective layer of the highly heat-resistant segment has a thickness of 1.0 to 6.0 μm. The honeycomb according to claim 1 or 2, wherein 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 extending direction of the cell 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.

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