JP2014094354A - Honeycomb filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively prevent the occurrence of cracks caused by thermal stress at a part contacting the sealing part of a honeycomb structure and the sealing part while a pressure loss level is made uniform by aligning the length of the effective filter region of each cell and the degree of freedom is given in the selection of materials for the honeycomb structure and the sealing part.SOLUTION: In the end of at least one side in an extending direction of a honeycomb structure 10, a thermal stress relaxing layer 20 made by at least one layer is formed between a cell wall 12 and a sealing part 21. The thermal stress relaxing layer 20 relaxes thermal stress caused by the difference of thermal expansion coefficient between the cell wall 12 and the sealing part 21 and is formed so as to extend in a cell 11 direction deeper than the sealing part 21. The constituents of the honeycomb structure 10 and the sealing part 21 are different.

Description

  The present invention relates to a honeycomb filter used as an exhaust gas purifying filter for removing particulate matter (PM) contained in exhaust gas of an internal combustion engine, particularly a diesel engine.

  As a filter that is provided in an exhaust passage of an internal combustion engine and collects PM contained in exhaust gas, an exhaust gas purification filter using a porous ceramic material is widely used. In particular, regarding PM contained in exhaust gas of diesel vehicles, emission regulations are being strengthened in stages in Japan, the United States, and Europe together with nitrogen oxides (NOx). In order to conform to such regulations, development of diesel particulate filters (DPFs) for collecting PM has been actively promoted. At present, a wall flow type honeycomb filter having a honeycomb structure is mainly used as a DPF.

  The honeycomb filter has a honeycomb structure in which a large number of cells made of through holes are regularly formed with the axial direction of the honeycomb filter as the extending direction. The honeycomb structure is formed of a porous ceramic fired body, and each cell is sealed with a sealing portion in which cells on one side in the axial direction (stretching direction) are adjacent to each other. Sealing portions are arranged in a checkered pattern at the axial end of the honeycomb filter.

  By the way, in a honeycomb filter, although a thermal load is repeatedly applied, there is a problem that cracks are generated due to thermal stress generated at that time. The thermal stress is due to the difference in thermal expansion coefficient between the honeycomb structure and the sealing portion, and is concentrated at the boundary portion between the honeycomb structure and the sealing portion, and cracks are generated.

  In order to prevent the occurrence of cracks due to such thermal stress, for example, Patent Document 1 discloses a configuration in which the sealing thickness (distance into which the sealing portion enters the cell) is not uniform among a plurality of sealing portions. Is disclosed. According to this, by making the sealing thickness non-uniform between the plurality of sealing portions, the imaginary line connecting the boundary portion between the sealing portion where the thermal stress is concentrated and the wall surface of the cell is arranged in a straight line. Or a continuous pattern, and thermal stress can be dispersed to prevent generation of cracks.

  Patent Document 2 discloses an appropriate range relationship between the porosity of a columnar body (honeycomb structure) serving as a filter and the porosity of a filler serving as a plugging portion (sealing portion). . Specifically, a configuration is described in which when the porosity of the columnar body is 20 to 80%, the porosity of the plugged portion is 90% or less and 0.15 to 4 times the porosity of the columnar body. ing. When the porosity of the columnar body and the porosity of the filler satisfy such conditions, a gap occurs between the filler and the wall (columnar body) due to thermal stress during production or use, It is possible to prevent the occurrence of cracks in the wall portion of the filler or the portion in contact with the filler.

Japanese Patent No. 3012167 Japanese Patent No. 4386830

  However, in the technique of Patent Document 1, since the sealing thickness is not uniform among the plurality of sealing portions, the lengths (the lengths in the axial direction) of the effective filter regions in each cell are not uniform. The effective filter area is an area that effectively functions as a filter for removing PM. If the lengths of the effective filter regions are not uniform, the pressure loss level of each cell becomes non-uniform, and the PM collection is biased (for example, PM is collected in a concentrated manner in cells having a low pressure loss level). As a result, the filter function deteriorates in a short period of time.

  On the other hand, the technology of Patent Document 2 does not define any constituents of the columnar body and the filler, and defines only the relationship between the porosity of the columnar body and the filler in a range that does not differ greatly. It is described that the difference between the coefficient of thermal expansion and the coefficient of thermal expansion of the filler can be reduced. However, as an example, only examples using the same constituent components for the columnar body and the filler are described, and when the actual component was created, the constituent components of the columnar body and the filler were made different. However, even if it was manufactured so as to satisfy the specified porosity relationship between the columnar body and the filler, cracks due to thermal stress could not be prevented as expected. This is considered to be due to the fact that the degree of influence of the thermal expansion coefficient due to the porosity is not necessarily high, and the effect is limited. In view of the above, it can be said that the technique of Patent Document 2 approximates not only the porosity of the columnar body and the filler, but also the constituent components.

  However, in order to prevent the occurrence of cracks due to thermal stress, the composition of the columnar body and the filler and the porosity are approximated. The degree of freedom becomes low.

  Further, the columnar body is preferably a constituent component and a porosity so that the function of a filter that allows exhaust gas to pass through after collecting PM contained therein can be exhibited to the maximum. It is preferably a constituent component and a porosity so that the function as a sealing portion such as blocking the passage of exhaust gas with certainty and sealing the cell can be maximized. In order to prevent the occurrence of cracks due to thermal stress in the columnar body and the filler having different functions as described above, imposing restrictions such as approximating the constituent components and the porosity is not possible. Or in both, there is a risk of impairing the function.

  The present invention has been made in view of the above problems, and its purpose is to make the pressure loss level uniform by aligning the length of the effective filter region of each cell, and to select the material for the honeycomb structure and the sealing portion. It is to prevent the occurrence of cracks due to thermal stress in the contact portion and the sealing portion of the honeycomb structure with the degree of freedom.

  In order to solve the above problems, a honeycomb filter of the present invention includes a honeycomb structure having a plurality of cells extending in one direction formed by being partitioned by cell walls, and extending in the extending direction of the plurality of cells. In the honeycomb filter in which the cells on the one side are alternately sealed by the sealing portions between adjacent cells, the honeycomb structure and the sealing portion have different constituent components, and the stretch in the honeycomb structure At least one end in the direction is formed with at least one thermal stress relaxation layer between the sealing portion and the cell wall, and the thermal stress relaxation layer is formed between the honeycomb structure and the sealing member. It relieves the thermal stress caused by the difference in thermal expansion coefficient with the stopper, and is formed by extending in the depth direction of the cell from the sealing part, and the thermal expansion coefficient of the honeycomb structure When Characterized in that it has a thermal expansion coefficient between the thermal expansion coefficient of Kifutome portion.

  According to the above configuration, since the constituents (constituent components) of the honeycomb structure and the sealing portion are different, it is possible to select constituent components capable of maximizing the function as an exhaust gas filter for the honeycomb structure. For the sealing portion, a constituent component that can exert the function as the sealing portion to reliably prevent the passage of exhaust gas and seal the cell can be selected. Thereby, while improving the function of each of a honeycomb structure and a sealing part, the selection range of material can be expanded and manufacture of a honeycomb filter can be made easy.

  By the way, when the constituent components of the honeycomb structure and the sealing portion are made different as described above, the thermal stress generated by the difference in thermal expansion coefficient between the honeycomb structure and the sealing portion causes the sealing portion of the honeycomb structure to Although there is a problem that a crack occurs in a contact part or a sealing part, according to the above configuration, a thermal stress relaxation layer is provided between the sealing part and the cell wall. It is solved by that.

  The thermal stress relaxation layer is formed so as to extend in the depth direction of the cell (hereinafter referred to as the cell depth direction) from the sealing portion, thereby forming a step between the sealing portion and the thermal stress relaxation layer. ing. By providing such a step, a virtual line connecting the boundary portion between the cell wall and the thermal stress relaxation layer (virtual line connecting the end surface of the thermal stress relaxation layer in the cell depth direction), the thermal stress relaxation layer, and the sealing portion Can be dispersed on at least two lines (virtual line connecting end faces in the cell depth direction in the sealing portion) connecting the boundary portions with (action A). Moreover, the stress relaxation layer is made into two or more layers, the length of each layer extending in the cell depth direction is changed, and the position of the end surface in the cell depth direction is shifted (shifted) to be dispersed on three or more lines. be able to. In the configuration in which such a step is not provided, virtual lines that connect the boundary portions between the cell walls and the sealing portion (virtual lines that connect the end surfaces of the sealing portion in the cell depth direction) are arranged in a straight line. As a result, the locations where thermal stress occurs are concentrated on this single line.

  Further, by providing a step between the thermal stress relaxation layer and the sealing portion, a space is secured on the side opposite to the side in contact with the cell wall in the thermal stress relaxation layer, and the thermal stress relaxation layer expands to the space side. It becomes possible. As a result, the difference between the thermal expansion coefficient between the honeycomb structure and the thermal stress relaxation layer, or the difference between the thermal expansion coefficients between the thermal stress relaxation layer and the sealing portion, may cause The thermal stress generated at the boundary portion and the boundary portion between the thermal stress relaxation layer and the sealing portion is relaxed (reduced) (action B).

  Further, since the thermal expansion coefficient of the thermal stress relaxation layer is set between the thermal expansion coefficient of the honeycomb structure and the thermal expansion coefficient of the sealing part, the thermal expansion between the honeycomb structure and the sealing part is performed. The difference in the coefficient of expansion changes into a difference in thermal expansion coefficient between the honeycomb structure and the thermal stress relaxation layer and a difference in thermal expansion coefficient between the thermal stress relaxation layer and the sealing portion. It becomes smaller. As a result, the thermal stress itself generated at the boundary portion between the cell wall and the thermal stress relaxation layer and the boundary portion between the thermal stress relaxation layer and the sealing portion is alleviated (reduced) (action C).

  As described above, according to the above configuration, the thermal stress relaxation layer is formed and the step is provided, so that the boundary portion between the cell wall and the thermal stress relaxation layer and the boundary portion between the thermal stress relaxation layer and the sealing portion are formed. Each of the generated thermal stresses on a plurality of lines and the thermal stress relaxation layer expands to the space side, so that the boundary between the cell wall and the thermal stress relaxation layer and the thermal stress relaxation layer and the sealing portion By reducing the thermal stress itself generated at each boundary portion B and the thermal expansion coefficient of the thermal stress relaxation layer between the thermal expansion coefficient of the honeycomb structure and the thermal expansion coefficient of the sealing portion, Due to synergy with the action C that relieves thermal stress itself generated at the boundary portion between the thermal stress relaxation layer and the boundary portion between the thermal stress relaxation layer and the sealing portion, the portion in contact with the sealing portion of the honeycomb structure or the sealing It is effective that cracks due to thermal stress occur in the stop. It is possible to prevent manner.

  The honeycomb filter of the present invention may further have a configuration in which the thermal expansion coefficient of the honeycomb structure is smaller than the thermal expansion coefficient of the sealing portion.

  In the honeycomb filter of the present invention, the sealing portion and the thermal stress relaxation layer may have different compositions. According to this, the selection range of the material for the sealing portion and the thermal stress relaxation layer is widened, and the thermal expansion coefficient can be easily set.

  In the honeycomb filter of the present invention, the honeycomb structure may include silicon nitride as a main component, and the sealing portion may include aluminum oxide as a main component.

  In order to solve the above-described problem, the method for manufacturing a honeycomb filter of the present invention includes immersing an end portion of the honeycomb structure in a stretching direction in a first material dispersion having fluidity to form the thermal stress relaxation layer. And a step of immersing an end portion of the honeycomb structure on which the thermal stress relaxation layer is formed in a second material dispersion having fluidity to form the sealing portion.

  By setting it as such a procedure, the honey-comb filter of this invention can be manufactured easily.

  In the method for manufacturing a honeycomb filter of the present invention, the fluidity of the first material dispersion is preferably higher than the fluidity of the second material dispersion.

  By increasing the fluidity of the first material dispersion, the height (encapsulation depth) of the inner end face of the thermal stress relaxation layer can be made uniform between the cells, so the effective filter area length of each layer can be reduced. It can be aligned more effectively. In addition, since the thickness of the layer is reduced by increasing the fluidity of the first material dispersion, a plurality of layers with different encapsulation depths can be easily formed even when the thermal stress relaxation layer is composed of a plurality of layers. Can be formed. The second material dispersion that becomes the sealing portion needs to remain without dropping from the cell and seal the cell, and therefore the one having low fluidity is preferable.

  According to the present invention, the honeycomb structure is sealed while the effective filter region length of each cell is made uniform so that the pressure loss level is uniform, and the material of the honeycomb structure and the sealing portion is flexible. There is an effect that it is possible to prevent the occurrence of cracks due to thermal stress in the portion in contact with the portion or the sealing portion.

It is a schematic cross section of a plane parallel to the axial direction of a honeycomb filter according to an embodiment of the present invention. It is a perspective view which shows the external appearance of the said honey-comb filter. It is a schematic cross section which expands and shows the edge part of the cell in which the thermal stress relaxation layer which consists of one layer in the said honey-comb filter was provided. (A) and (b) are both schematic cross-sectional views showing an enlarged end portion of a cell provided with a thermal stress relaxation layer of a modification of the honeycomb filter. It is the schematic cross section which expanded the thermal stress relaxation layer of the modification which can be used as a thermal stress relaxation layer. It is explanatory drawing which shows the effective filter area | region of the said honey-comb filter. FIG. 5 is a schematic cross-sectional view of a plane parallel to the axial direction of a honeycomb filter according to another embodiment of the present invention.

  Hereinafter, the present invention will be described with reference to embodiments. FIG. 1 is a schematic cross-sectional view of a plane parallel to the axial direction of a honeycomb filter according to an embodiment of the present invention. FIG. 2 is a perspective view showing an overview of the honeycomb filter.

  As shown in FIG. 1 or FIG. 2, the honeycomb filter 1 has a honeycomb structure 10 made of a cylindrical porous ceramic fired body. A plurality of cells 11 extending in one direction are formed inside the cylindrical main body of the honeycomb structure 10. Each cell 11 has a cross-sectional shape that is substantially square in a direction perpendicular to the axial direction (cell extending direction) and is defined by a porous cell wall 12. The porous cell wall 12 serves as a particulate matter (hereinafter, PM) collecting member.

  Each cell 11 provided in the honeycomb structure 10 is sealed with a sealing portion 21 alternately in which cells on one side in the extending direction are adjacent to each other. At the axial end of the honeycomb filter 1, the sealing portions 21 are arranged in a checkered pattern. The honey-comb filter 1 has the characteristics in the structure of the edge part in which this sealing part 21 was provided. This will be described later.

  Further, the outer peripheral portion of the honeycomb structure 10 is covered with the outer peripheral covering layer 15. The outer periphery covering layer 15 is made of a ceramic layer, and is formed by firing an outer periphery covering material applied to the outer periphery of the honeycomb structure 10. In addition, in FIG. 1, description of the outer periphery coating layer 15 is abbreviate | omitted.

  As shown in FIG. 1, the honeycomb filter 1 having such a configuration is arranged such that the axial direction, which is also the extending direction of the cells 11, is parallel to the flow of exhaust gas. The exhaust gas flows in from the cell (inflow side cell) 11 in which the sealing portion 21 is not packed at the end located on the upstream side of the flow. The exhaust gas that has flowed into the cell passes through the micropores of the porous cell wall 12, moves to another cell (outflow side cell) 11 adjacent to the flowed cell 11, and flows out from there. As the exhaust gas passes through the fine holes in the cell wall 12, PM contained in the exhaust gas is collected in the cell wall 12. The collected PM is removed from the cell wall 12 by regenerating and heating the honeycomb filter 1, and the honeycomb filter 1 is regenerated.

  In FIG. 2, the honeycomb structure 10 is exemplified by a cylindrical shape in which the cross-sectional shape of the surface perpendicular to the axial direction of the honeycomb filter 1 is circular, but the cross-sectional shape is not particularly limited. For example, it may be oval, square, rectangular, or polygonal. Such a honeycomb structure 10 can be molded in advance into a desired shape by using an extruder. Further, the optimum value of the cross-sectional size of the plane perpendicular to the axial direction of the honeycomb filter 1 is determined by the engine displacement.

  On the other hand, the cross-sectional shape of the cell 11 is preferably substantially square. However, it is not necessarily limited to this, and other shapes may be used. The thickness of the cell wall 12 is not particularly limited, and may be 0.2 to 0.4 mm, for example. Further, the number of cells in the unit area is not particularly limited, and may be, for example, 200 to 300 cpsi. Although the thickness of the outer peripheral coating layer 15 is not particularly limited, it is generally set to 0.3 mm to 1.0 mm.

  Moreover, as a material of each part in the honey-comb filter 1, the existing existing material can be used. For example, the honeycomb structure 10 is obtained by sintering or reaction sintering a composition containing the material constituting the honeycomb structure 10 and conventionally known sintering aids, conventionally known various binders, and the like. Can be formed.

  Examples of the ceramic material that is a constituent of the honeycomb structure 10 include nitride ceramics such as silicon nitride, aluminum nitride, boron nitride, and titanium nitride, cordierite, aluminum oxide (alumina), silica, mullite, and aluminum titanate. Examples thereof include oxide ceramics, carbide ceramics such as silicon carbide, zirconium carbide, titanium carbide, tantalum carbide, and tungsten carbide. Among these, silicon nitride is particularly preferable from the viewpoint of strength and heat resistance. Note that silicon nitride also includes sialon in which part of silicon and nitrogen in silicon nitride is replaced with aluminum and oxygen, respectively.

  As the sealing material forming the sealing portion 21, ceramic clay such as aluminum oxide (alumina), aluminum titanate, silicon carbide, silicon nitride, cordierite, mullite, apatite, or cement material can be used. . These may be used alone or in combination. Among these, aluminum oxide is particularly preferable from the viewpoint of versatility as a cement material.

  Conventionally, as the sealing material (filler) of the sealing portion, it is considered preferable to use the same constituent components as those of the honeycomb structure in order to reduce the difference in the coefficient of thermal expansion with the honeycomb structure. Yes. Further, according to Patent Document 2, not only the constituent components but also the porosity range of the honeycomb structure and the sealing portion are related to close values.

  However, for the honeycomb structure having a filter function of passing exhaust gas after collecting PM contained in the exhaust gas, the sealing portion reliably blocks the passage of the exhaust gas and seals the cells. In other words, the honeycomb structure and the sealing portion should select constituent components suitable for the respective functions and set the porosity.

  As will be described later, the honeycomb filter 1 has a feature in the structure of the end portion where the sealing portion 21 is provided, so that the constituent components of the sealing portion 21 are independent of the constituent components of the honeycomb structure 10. The honeycomb structure 10 and the sealing portion 21 are made of different constituent components.

  The outer peripheral coating layer 15 is made of a ceramic layer, and a material obtained by blending inorganic particles such as inorganic balloon, colloidal silica, bentonite, an inorganic binder, or the like with the material of the honeycomb structure 10 described above is used.

  Next, the structure of the end portion provided with the sealing portion 21 which is a characteristic configuration of the honeycomb filter 1 will be described. As shown in FIG. 1, a thermal stress relaxation layer 20 including at least one layer is formed between the cell wall 12 and the sealing portion 21. The thermal stress relaxation layer 20 relaxes thermal stress generated due to the difference in coefficient of thermal expansion between the cell wall 12 and the sealing portion 21.

  FIG. 3 is a schematic cross-sectional view showing an enlarged end portion of the cell 11 provided with a single layer of thermal stress relaxation layer 20. As shown in FIG. 3, the thermal stress relaxation layer 20 is formed by extending in the depth direction of the cell 11 (cell depth direction) from the sealing portion 21, and the thermal stress relaxation layer 20, the sealing portion 21, and the like. A step is formed between the two.

  When the encapsulation depth of the thermal stress relaxation layer 20 is T1 and the encapsulation depth of the sealing portion 21 is T2, T1 and T2 are in a relationship of T1> T2, and the thermal stress relaxation layer 20 is more sealed than the sealing portion 21. Further, it is inserted deeper from the end of the cell 11 toward the back side of the cell 11. The encapsulating depth of the layer is the axial length of the layer starting from the end of the cell 11.

  By forming a step between the sealing portion 21 and the thermal stress relaxation layer 20, an imaginary line connecting the boundary portion between the cell wall 12 and the thermal stress relaxation layer 20 (an end surface in the cell depth direction in the thermal stress relaxation layer 20). Imaginary line connecting L1 (see FIG. 1) and a virtual line connecting the boundary portion between the thermal stress relaxation layer 20 and the sealing portion 21 (virtual line connecting the end surfaces of the sealing portion in the cell back direction) L2 (FIG. 1) (See A)) (action A). In the configuration in which such a step is not provided, virtual lines that connect the boundary portions between the cell walls and the sealing portion (virtual lines that connect the end surfaces of the sealing portion in the cell depth direction) are arranged in a straight line. As a result, the locations where thermal stress occurs are concentrated on this single line.

  Further, by providing a step between the thermal stress relaxation layer 20 and the sealing portion 21, a space is secured on the side opposite to the side in contact with the cell wall 12 in the thermal stress relaxation layer 20, and the thermal stress relaxation layer 20 It becomes possible to expand to the space side.

  Thereby, due to the difference in thermal expansion coefficient between the honeycomb structure 10 and the thermal stress relaxation layer 20, the thermal stress generated at the boundary portion between the thermal stress relaxation layer 20 and the cell wall 12 indicated by the arrow P1 in FIG. The thermal stress generated at the boundary portion between the thermal stress relaxation layer 20 and the sealing portion 21 indicated by the arrow P2 in FIG. 3 due to the difference in thermal expansion coefficient between the thermal stress relaxation layer 20 and the sealing portion 21. Mitigated (reduced) (action B).

  Here, the encapsulation depth T1 of the thermal stress relaxation layer 20 is preferably in a range larger than 1.1 times and smaller than 2 times the encapsulation depth T2 of the sealing portion 21. If it is 1.1 times or less, the level difference is too small, and it becomes impossible to ensure the ability of the thermal stress relaxation layer 20 to release and relax the thermal stress to the space opposite to the cell wall 12 side. On the other hand, if it exceeds twice, the thermal stress relaxation layer 20 becomes unnecessarily long, and the length of an effective filter region described later becomes short.

  Further, when the thermal stress relaxation layer 20 has two or more layers, the flow extending in the cell depth direction of each layer of the thermal stress relaxation layer 20 can be varied to shift (shift) the position of the end surface in the cell depth direction. preferable. With such a configuration, it can be dispersed on three or more lines.

  Furthermore, the thermal stress relaxation layer 20 has a thermal expansion coefficient between the thermal expansion coefficient of the cell wall 12 and the thermal expansion coefficient of the sealing portion 21. That is, if the thermal expansion coefficient of the cell wall 12 is W1, the thermal expansion coefficient of the thermal stress relaxation layer 20 is W2, and the thermal expansion coefficient of the sealing portion 21 is W3, W1 <W2 <W3 or W1> W2> W3. Satisfied relationship.

  With such a configuration, the difference in thermal expansion coefficient between the honeycomb structure 10 and the sealing portion 21 is different from the difference in thermal expansion coefficient between the honeycomb structure 10 and the thermal stress relaxation layer 20. Instead of the difference in thermal expansion coefficient between the thermal stress relaxation layer 20 and the sealing portion 21, the difference in thermal expansion coefficient itself is reduced. Thereby, the thermal stress generated at the boundary portion between the cell wall 12 and the thermal stress relaxation layer 20 indicated by the arrow P1 in FIG. 3, and the thermal stress relaxation layer 20 and the sealing portion 21 indicated by the arrow P2 in FIG. Thermal stress generated at the boundary portion is relaxed (reduced) (action C).

  When the thermal stress relaxation layer 20 has two or more layers, the thermal expansion coefficient of each layer of the thermal stress relaxation layer 20 is between the thermal expansion coefficient W1 of the cell wall 12 and the thermal expansion coefficient W3 of the sealing portion 21. It is preferable that the value be a value that gradually closes the difference. That is, the first layer, the second layer, the third layer,... From the side close to the cell wall 12, and the thermal expansion coefficients thereof are W2-1 (first layer), W2-2 (second layer), W2 in order. -3 (third layer)..., W1 <W3, it is preferable that W2-1 <W2-2 <W2-3 according to the relationship, and if W1> W3 , W2-1> W2-2> W2-3 is preferably satisfied.

  However, when the thermal stress relaxation layer 20 has two or more layers as described above, the thermal expansion coefficients of the layers of the thermal stress relaxation layer 20 may all be the same or some of them may be the same. That is, W2-1 = W2-2 = W2-3 when W1 <W3 or W1> W3, or W2-1 = W2-2> W2-3 when W1> W3. As described above, the thermal expansion coefficients of all the layers or some of the layers may be the same.

When the cell wall 12, the thermal stress relaxation layer 20, the sealing portion 21, and the thermal stress relaxation layer 20 are composed of a plurality of layers, the difference in thermal expansion coefficient between adjacent ones including those layers is at most. It is desirably 4 × 10 ⁻⁶ / ° C. or lower, and more preferably 3 × 10 ⁻⁶ / ° C. or lower.

  As described above, the thermal stress relaxation layer 20 is formed between the cell wall 12 and the sealing portion 21 to provide a step, so that the boundary portion between the cell wall 12 and the thermal stress relaxation layer 20 and the thermal stress relaxation layer 20 are provided. Between the cell wall 12 and the thermal stress relaxation layer 20 due to the expansion of the thermal stress relaxation layer 20 to the space side. The effect B of relaxing the thermal stress itself generated at the boundary portion and the boundary portion between the thermal stress relaxation layer 20 and the sealing portion 21, and the thermal expansion coefficient of the thermal stress relaxation layer 20 are combined with the thermal expansion coefficient of the honeycomb structure 10. The thermal stress itself generated at the boundary portion between the cell wall 12 and the thermal stress relaxation layer 20 and at the boundary portion between the thermal stress relaxation layer 20 and the sealing portion 21 is made between the thermal expansion coefficient of the stopper portion 21. Honeycomb structure due to synergy with action C A crack due to parts or sealing portion 21 which contacts the sealing portion 21 of the body 10 to the thermal stress is generated can be effectively prevented.

  By providing such a thermal stress relaxation layer 20, it becomes possible to make the constituent components different between the honeycomb structure 10 and the sealing portion 21, and the honeycomb structure 10 has a function as an exhaust gas filter. Can be selected, and the sealing portion 21 has a constituent component capable of maximizing the function as the sealing portion such as sealing the cell by reliably preventing the passage of exhaust gas. You can choose. Thereby, while improving the function of each of the honeycomb structure 10 and the sealing part 21, the selection range of material can be expanded and manufacture of the honeycomb filter 1 can be made easy.

  In FIG. 3, the configuration in which the thermal stress relaxation layer 20 is one layer is illustrated. However, as described above, the thermal stress relaxation layer 20 may have two layers, three layers, or more layers. 4A and 4B are schematic cross-sectional views showing an enlarged end portion of a cell provided with a thermal stress relaxation layer according to a modification. (A) The thermal stress relaxation layer is composed of the first thermal stress relaxation layer 20a and the second thermal stress relaxation layer 20b, and (b) is the first to third layers of the thermal stress relaxation layer. Thermal stress relaxation layers 20a-20c.

  FIG. 5 is an explanatory diagram showing an effective filter region of the honeycomb filter. A portion excluding a region in contact with the thermal stress relaxation layer 20 disposed at both ends in the axial direction of the honeycomb filter 1 is an effective filter region. In other words, the effective filter region extends in the innermost surface end of the thermal stress relaxation layer 20 extending in the innermost cell direction of the input side cell 11 and in the innermost cell direction of the output side cell 11. It is the distance between the inner surface edges of the thermal stress relaxation layer 20.

  In the honeycomb filter 1, in each cell, the thermal stress relaxation layer 20 is provided between the cell wall 12 and the sealing portion 21 to provide a step, and the difference in thermal expansion coefficient is alleviated. The crack which originates in a thermal stress in the part which contacts the sealing part 21 of the body 10, or the sealing part 21 is prevented. Therefore, as shown in FIG. 5, the effective filter area in each cell 11 can be made uniform, and the pressure loss level can be made uniform.

  In the honeycomb filter 1 shown in FIG. 1, the thermal stress relaxation layer 20 is provided at both ends of the honeycomb filter 1. However, the thermal stress relaxation layer 20 is provided at least at one end. Just do it.

  FIG. 6 is a schematic cross-sectional view of a plane parallel to the axial direction of a honeycomb filter according to another embodiment of the present invention. As shown in FIG. 6, in the honeycomb filter 1A, the thermal stress relaxation layer 20 is provided only at one end portion in the axial direction, and the other end portion is sealed only by the conventional sealing portion 21. It has stopped. In the honeycomb filter 1A adopting the configuration in which the thermal stress relaxation layer 20 is provided only at the one end portion, as shown in FIG. 6, the end portion side where the thermal stress relaxation layer 20 is provided is the flow of exhaust gas. It is arranged on the downstream side.

  In the honeycomb filter, more heat load is applied to the downstream side of the exhaust gas flow than to the upstream side. Therefore, by setting at least the side disposed on the downstream side of the exhaust gas flow as the side on which the thermal stress relaxation layer 20 is provided, the generation of cracks due to thermal stress can be effectively prevented.

  The honeycomb filters 1 and 1A exemplify a so-called integral type in which the honeycomb structure 10 is formed of one porous ceramic fired body. However, a divided type in which a honeycomb segment body, which is a plurality of porous ceramic fired bodies formed in a prismatic shape, is bonded to each other through a joint portion may be used.

  Next, a procedure of a sealing process in which a plurality of cells 11 of the honeycomb structure 10 are sealed with the sealing portion 21 by forming the thermal stress relaxation layer 20 will be described.

  First, the end portion in the axial direction (stretching direction) of the honeycomb structure 10 is immersed in a fluid first material dispersion to form the thermal stress relaxation layer 20. In addition, in the edge part of the honeycomb structure 10 to immerse, the cell which should not be sealed is block | closed with the film etc. Here, in the case where the thermal stress relaxation layer 20 is composed of a plurality of layers, the thermal stress relaxation layer 20 is formed in order from the first layer adjacent to the cell wall 12 while gradually decreasing the depth of immersing the end portion. Moreover, when changing a thermal expansion coefficient in each layer used as the thermal stress relaxation layer 20, the 1st material dispersion liquid to immerse is changed.

  When the thermal stress relaxation layer 20 is formed, the end of the honeycomb structure 10 on the side where the thermal stress relaxation layer 20 is formed is then immersed in a second material dispersion having fluidity and sealed. Part 21 is formed.

  Comparing the first material dispersion that becomes the thermal stress relaxation layer 20 and the second material dispersion that becomes the sealing portion 21, the fluidity of the first material dispersion is the fluidity of the second material dispersion. It is preferable to adjust higher.

  By increasing the fluidity, the height (encapsulation depth) of the inner end face of the thermal stress relaxation layer 20 can be made uniform among the cells. In addition, since the thickness of the layer is reduced by increasing the fluidity, even when the thermal stress relaxation layer 20 is composed of a plurality of layers, a plurality of layers having different encapsulation depths can be easily formed.

  On the other hand, since the 2nd material dispersion liquid used as the sealing part 21 needs to remain without dropping from the cell 11 and seal the cell 11, what has low fluidity | liquidity is preferable. In addition, since the effective filter area is determined at the inner surface end of the thermal stress relaxation layer 20 extending most in the depth direction of the cell 11, the fluidity of the second material dispersion is low, so that the sealing portion Even if the heights of 21 are not aligned, there is no influence.

  The thermal stress relaxation layer 20 also seals the cell 11 together with the sealing portion 21. Therefore, the method of sealing the cell 11 with the thermal stress relaxation layer 20 composed of a plurality of layers and the sealing portion 21 with such a thermal stress relaxation layer 20 composed of a plurality of layers is as follows. When the pore diameter is large, for example, it is effective as a method for sealing cells having a large pore diameter in a honeycomb body in which the cell pore diameters on the inlet side and the outlet side of the exhaust gas are changed. That is, the method of the present invention has an excellent characteristic that it is possible to gradually close the opening with a plurality of layers with a large pore diameter.

  The present invention will be described in more detail with reference to examples. In the examples and comparisons described below, the porosity was measured using an Archimedes density meter, and the thermal expansion coefficient was measured using a differential thermal expansion meter.

Example 1
Sealing a plurality of cells 11 of the honeycomb structure 10 made of silicon nitride (Si ₃ N ₄ ) by providing a single layer of thermal stress relaxation layer 20 between the sealing portion 21 and the cell wall 12. Stop processing was performed. The used honeycomb structure 10 had a porosity of 60% and a thermal expansion coefficient of 3 × 10 ⁻⁶ / ° C.

For the thermal stress relaxation layer 20, a powder obtained by mixing aluminum oxide (alumina: Al ₂ O ₃ ) and cordierite (2MgO · 2Al ₂ O ₃ · 5SiO ₂ ) at 50% (mass ratio) is made into a slurry. used. Alumina cement was used for the sealing part 21, and the alumina cement was used in a slurry state.

After forming the slurry (first material dispersion) to be the thermal stress relaxation layer 20 into a thin film shape with respect to the honeycomb structure 10, the alumina cement slurry (second material dispersion) to be the sealing portion 21 is formed. The sealing part 21 was manufactured. The thermal expansion coefficient of the thermal stress relaxation layer 20 was 4.6 × 10 ⁻⁶ / ° C., and the thermal expansion coefficient of the sealing portion 21 was 7.2 × 10 ⁻⁶ / ° C.

(Example 2)
Sealing process using the same honeycomb structure 10 as in Example 1 to seal a plurality of cells 11 by providing a two-layered thermal stress relaxation layer 20 between the sealing portion 21 and the cell wall 12 Went.

  For the first thermal stress relaxation layer 20a adjacent to the cell wall 12, a powder mixed at a ratio of 33% aluminum oxide and 67% cordierite was used as a slurry. For the second thermal stress relaxation layer 20b, powder mixed in a proportion of 67% aluminum oxide (mass ratio) and 33% cordierite (mass ratio) was used as a slurry. Alumina cement was used for the sealing part 21, and the alumina cement was used in a slurry state.

A slurry (first material dispersion) that becomes the first thermal stress relaxation layer 20a is formed in a thin film shape on the honeycomb structure 10 and then the slurry that becomes the second thermal stress relaxation layer 20b ( The first material dispersion) was formed into a thin film. Then, the sealing part 21 was manufactured by filling alumina cement slurry (second material dispersion) to be the sealing part 21. The thermal expansion coefficient of the first thermal stress relaxation layer 20a is 3.7 × 10 ⁻⁶ / ° C., and the thermal expansion coefficient of the second thermal stress relaxation layer 20b is 5.4 × 10 ⁻⁶ / ° C. The thermal expansion coefficient of the part 21 was 7.2 × 10 ⁻⁶ / ° C.

(Example 3)
Sealing process in which the same honeycomb structure 10 as in Example 1 is used to seal a plurality of cells 11 by providing a single layer of thermal stress relaxation layer 20 between the sealing portion 21 and the cell wall 12. Went.

For the thermal stress relaxation layer 20, powder of mullite (3Al ₂ O ₃ .2SiO ₂ ) was used in a slurry state. Alumina cement was used for the sealing part 21, and the alumina cement was used in a slurry state.

A slurry (first material dispersion) to be the thermal stress relaxation layer 20 was formed in a thin film on the honeycomb structure 10. Then, the sealing part 21 was manufactured by filling an alumina cement slurry (second material dispersion) to be the sealing part 21. The thermal expansion coefficient of the thermal stress relaxation layer 20a was 5 × 10 ⁻⁶ / ° C., and the thermal expansion coefficient of the sealing portion 21 was 7.2 × 10 ⁻⁶ / ° C.

(Comparative Example 1)
Using the same honeycomb structure 10 as in Example 1, a sealing process was performed in which the plurality of cells 11 were sealed only by the sealing portion 21 without providing the thermal stress relaxation layer 20. Alumina cement was used for the sealing part 21, and the alumina cement was used in a slurry state.

The honeycomb structure 10 was filled with an alumina cement slurry to produce a sealing portion 21. The thermal expansion coefficient of the sealing part 21 was 7.2 × 10 ⁻⁶ / ° C.

(Comparative Example 2)
Sealing process in which the same honeycomb structure 10 as in Example 1 is used to seal a plurality of cells 11 by providing a single layer of thermal stress relaxation layer 20 between the sealing portion 21 and the cell wall 12. Went.

However, as the thermal stress relaxation layer 20, forsterite (2MgO.SiO ₂ ) powder was used in a slurry state. Alumina cement was used for the sealing part 21, and the alumina cement was used in a slurry state.

A slurry (first material dispersion) to be the thermal stress relaxation layer 20 was formed in a thin film on the honeycomb structure 10. Then, the sealing part 21 was manufactured by filling an alumina cement slurry (second material dispersion) to be the sealing part 21. The thermal expansion coefficient of the thermal stress relaxation layer 20a was 9.7 × 10 ⁻⁶ / ° C., and the thermal expansion coefficient of the sealing portion 21 was 7.2 × 10 ⁻⁶ / ° C.

  Table 1 shows the results of thermal shock tests performed on the honeycomb filters of Examples 1 to 3 and Comparative Examples 1 and 2. The presence / absence of a multi-stage structure in Table 1 represents the presence / absence of a step due to the thermal stress relaxation layer 20, and the relationship between the thermal expansion coefficients is the relationship between the thermal expansion coefficients of the thermal stress relaxation layer 20, the sealing portion 21, and the thermal stress relaxation layer 20. Whether or not is satisfied. The difference in thermal expansion coefficient (maximum) is that the thermal stress relaxation layer 20, the sealing portion 21, the thermal stress relaxation layer 20, and the thermal stress relaxation layer 20, including those layers, are adjacent to each other. The maximum value of the difference in coefficient of thermal expansion is shown. In the thermal shock test, the process of holding the honeycomb filter to be tested in a furnace at 600 ° C. for 2 hours and then air cooling was repeated 10 times. It was confirmed whether or not a crack occurred in the portion of the honeycomb structure 10 in contact with the sealing portion 21 or in the sealing portion 21.

As shown in Table 1, the difference between the honeycomb structure (cell wall) having a thermal expansion coefficient of 3 × 10 ⁻⁶ / ° C. and the sealing portion 21 having a thermal expansion coefficient of 7.2 × 10 ⁻⁶ / ° C. is expressed as thermal stress. For the honeycomb filters of Examples 1 to 3, which were made small by providing the relaxation layers 20 and 20a and the difference in coefficient of thermal expansion between adjacent ones was suppressed to 4 × 10 ⁻⁶ / ° C. or less, after the test In addition, no cracks occurred in the portion of the honeycomb structure 10 that was in contact with the sealing portion 21 or in the sealing portion 21.

On the other hand, in Comparative Example 1 in which the thermal stress relaxation layer 20 was not provided, the thermal stress caused by the difference in thermal expansion coefficient (4.2 × 10 ⁻⁶ / ° C.) between the cell wall 12 and the sealing portion 21. As a result, cracks occurred in the sealing portion 21. In Comparative Example 2 in which the thermal stress relaxation layer 20 having a thermal expansion coefficient of 9.7 × 10 ⁻⁶ / ° C. is provided between the cell wall 12 and the sealing portion 21, the thermal expansion of the thermal stress relaxation layer 20 is performed. The rate does not fall between the thermal expansion coefficients of the cell wall 12 and the sealing part 21, and the difference in thermal expansion coefficient between adjacent ones is 6.7 × 10 ⁻⁶ / ° C. Although there was an effect of dispersion and relaxation of thermal stress, as a result, cracks occurred in the honeycomb structure 10 and the sealing portion 21 that were in contact with the sealing portion 21.

  The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. Is also included in the technical scope of the present invention.

  The present invention can be suitably used as an exhaust gas purification filter for collecting particulate matter contained in exhaust gas of a diesel engine.

DESCRIPTION OF SYMBOLS 1, 1A Honeycomb filter 10 Honeycomb structure 11 Cell 12 Cell wall 15 Outer peripheral coating layer 20 Thermal stress relaxation layer 21 Sealing part

Claims (6)

A honeycomb structure having a plurality of cells extending in one direction formed by being partitioned by a cell wall, wherein one end portion in the extending direction of the plurality of cells is adjacent to each other and alternately sealed In the honeycomb filter sealed with
The honeycomb structure and the sealing portion have different constituent components,
At least at one end of the extending direction in the honeycomb structure, a thermal stress relaxation layer including at least one layer is formed between the sealing portion and the cell wall,
The thermal stress relaxation layer relaxes thermal stress generated due to a difference in thermal expansion coefficient between the honeycomb structure and the sealing portion, and extends in a depth direction of the cell from the sealing portion. And a thermal expansion coefficient between the thermal expansion coefficient of the honeycomb structure and the thermal expansion coefficient of the sealing portion.   The honeycomb filter according to claim 1, wherein a thermal expansion coefficient of the honeycomb structure is smaller than a thermal expansion coefficient of the sealing portion.   The honeycomb filter according to claim 1 or 2, wherein the sealing portion and the thermal stress relaxation layer have different compositions.   The honeycomb filter according to any one of claims 1 to 3, wherein the honeycomb structure includes silicon nitride as a main component and the sealing portion includes aluminum oxide as a main component. A method for manufacturing a honeycomb filter according to any one of claims 1 to 4,
A step of immersing an end portion of the honeycomb structure in a stretching direction in a first material dispersion having fluidity to form the thermal stress relaxation layer;
A step of immersing an end portion of the honeycomb structure on which the thermal stress relaxation layer is formed in a second material dispersion having fluidity to form the sealing portion. Manufacturing method.   The method for manufacturing a honeycomb filter according to claim 5, wherein the fluidity of the first material dispersion is higher than the fluidity of the second material dispersion.

Images