JP2016055282A - Honeycomb structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a honeycomb structure capable of preventing catalyst slurry from seeping out to an outside surface of an outer peripheral wall, improving the strength of the outer peripheral wall, and consequently, also improving the isostatic strength of the whole structure.SOLUTION: A honeycomb structure 1 includes: a honeycomb base material 2 having porous partitions 4 for partitioning the structure into multiple cells 5 extending from an inlet end surface 11 to be an entrance of fluid, to an outlet end surface 12 to be an exit of the fluid, and a porous outer peripheral wall 6 formed integrally with the partitions 4; and a coating layer 3 provided on at least a part of an outside surface of the outer peripheral wall 6. A part of the coating layer 3 enters pores of the outer peripheral wall 6, and a thickness of the part of the coating layer 3 entering the pores of the outer peripheral wall 6 is 1-90% of a thickness of the outer peripheral wall 6.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a honeycomb structure used for a filter or the like for collecting particulate matter contained in exhaust gas from a diesel engine or a gasoline engine, and particularly suitable for a filter or the like that needs to carry a catalyst. The present invention relates to a honeycomb structure.

  Particulate matter (particulate matter (PM)) is contained in exhaust gas from gasoline engines such as diesel engines and GDI (Gasoline Direct Injection) engines. This PM is mainly composed of carbon fine particles such as soot, and since it is recognized as carcinogenic, it must be prevented from being released into the atmosphere and is subject to strict emission regulations. Yes.

  Much research has been done to reduce PM emissions in order to comply with such strict emission regulations, but there are limits to reducing PM emissions by improving combustion technology. Is currently the only effective means of reducing PM emissions.

  As a filter for collecting PM, a wall flow type filter using a honeycomb structure is widely used because high PM collection efficiency can be obtained while suppressing pressure loss within an allowable range. A honeycomb structure used for a wall-flow filter has a porous partition wall that defines a plurality of cells extending from an inlet end surface on the exhaust gas inlet side to an outlet end surface on the exhaust gas outlet side, and an outer peripheral wall. doing. This honeycomb structure has a high PM collection efficiency by providing a plugging portion for plugging the opening end portion on the outlet end face side of a predetermined cell and the opening end portion on the inlet end face side of the remaining cells. Filter is obtained.

  Among such filters, a gasoline particulate filter (GPF) used for removing PM contained in the exhaust gas of a GDI engine is often used with a catalyst for exhaust gas purification carried on a partition wall. In this case, a honeycomb structure having a high porosity of 50% or more is used in order to keep the pressure loss within an allowable range even after supporting the catalyst.

  A relatively small honeycomb structure used for GPF is usually one in which partition walls and an outer peripheral wall are integrally formed. Such a honeycomb substrate is produced by simultaneously forming the partition walls and the outer peripheral wall by extrusion molding, and firing the obtained molded body, and the outer peripheral wall and the partition walls have the same porosity. Have.

  When the catalyst is supported on the partition walls of the honeycomb structure, a slurry containing the catalyst (catalyst slurry) is introduced into the cell by a conventionally known suction method or the like, and is adhered to the surface or pores of the partition walls, and then the temperature is increased. The treatment is performed and the catalyst contained in the catalyst slurry is baked on the partition walls. Here, when the honeycomb structure supporting the catalyst has a high porosity as described above, and the outer peripheral wall and the partition walls have the same porosity, the catalyst slurry introduced into the cell May pass through the pores of the wall and ooze out to the outer surface of the outer peripheral wall. Further, even when the catalyst is supported on the partition walls of the honeycomb structure in which the partition walls and the outer peripheral wall are separately formed, if the porosity of the outer peripheral wall is 35% or more, the catalyst slurry introduced into the cell May ooze out to the outside surface of the wall. When such catalyst slurry seeps out, there is a problem that workability deteriorates in the step of supporting the catalyst on the partition walls of the honeycomb structure. The step of supporting the catalyst on the honeycomb structure is performed with a part of the outer peripheral wall of the honeycomb structure being chucked (gripped). However, if the outer peripheral wall has a high porosity, sufficient strength can be obtained. In addition, there was a problem that the outer peripheral wall was easily damaged during chucking. Furthermore, if the entire honeycomb structure (partition walls and outer peripheral wall) has a high porosity, the isostatic strength of the honeycomb structure is lowered, and there is a problem that the honeycomb structure is easily damaged during transportation and actual use.

  Conventionally, as a technique for improving the strength of a honeycomb structure, a technique of attaching a reinforcing material to an outer peripheral wall is known. For example, Patent Document 1 discloses a honeycomb structure in which the outer peripheral portion of the honeycomb structure is reinforced with a material that disappears or scatters at a high temperature. Patent Document 2 discloses a honeycomb structure in which a material having a thermal expansion coefficient substantially equal to that of a catalyst is attached to the entire outer surface of the outer peripheral wall of the ceramic honeycomb structure before supporting the catalyst. Further, Patent Document 3 discloses a water-insoluble organic substance that is disposed so as to cover the outer peripheral portion of the cell structure and burns down by combustion on the outermost peripheral portion of the outer wall made of a porous body with a predetermined thickness. Alternatively, a honeycomb catalyst carrier having an impregnated portion impregnated with an inorganic substance is disclosed.

Japanese Unexamined Patent Publication No. 2000-809 JP 2001-871 A JP 2004-113887 A

  However, the reinforcing material in the honeycomb structure disclosed in Patent Document 1 disappears or scatters in the high temperature treatment when the catalyst is baked on the honeycomb structure, and thus does not contribute to the improvement of the strength of the honeycomb structure after the high temperature treatment. . Further, the reinforcing material in the honeycomb structure disclosed in Patent Document 2 is for eliminating a difference in thermal expansion between the inner side and the outer side of the outer peripheral wall, and has an effect of preventing exudation of the catalyst slurry and isostatic strength. The effect of improving is not expected so much. Furthermore, the honeycomb catalyst carrier disclosed in Patent Document 3 does not take into consideration the problem of seepage of catalyst slurry and insufficient strength.

  The present invention has been made in view of such circumstances, and can prevent the catalyst slurry from seeping out to the outer surface of the outer peripheral wall and improve the strength of the outer peripheral wall. An object is to provide a honeycomb structure having improved static strength.

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

[1] A porous partition wall that partitions and forms a plurality of cells extending from an inlet end surface that is a fluid inlet side to an outlet end surface that is a fluid outlet side, and a porous outer peripheral wall formed integrally with the partition wall And a coat layer disposed on at least a part of the outer surface of the outer peripheral wall, and the coat layer partially penetrates into the pores of the outer peripheral wall, A honeycomb structure in which a thickness of a portion of the outer peripheral wall of the coat layer penetrating into the pores is 1 to 90% of a thickness of the outer peripheral wall.

[2] A porous partition wall that partitions and forms a plurality of cells extending from an inlet end surface that is a fluid inlet side to an outlet end surface that is a fluid outlet side, and a porosity formed separately from the partition wall is 35% or more A honeycomb base material having a porous outer peripheral wall, and a coat layer disposed on at least a part of the outer surface of the outer peripheral wall, the coat layer including a part thereof in the pores of the outer peripheral wall A honeycomb structure in which the thickness of the portion of the coat layer that penetrates into the pores of the outer peripheral wall is 1 to 90% of the thickness of the outer peripheral wall.

[3] The honeycomb structure according to [1] or [2], wherein a thickness of a portion of the coat layer excluding a portion entering the pores of the outer peripheral wall is 70 μm or less.

[4] The honeycomb structure according to any one of [1] to [3], wherein the coat layer includes Si.

[5] The honeycomb structure according to [4], wherein the coat layer further contains Ti.

[6] The honeycomb structure according to any one of [1] to [5], wherein the honeycomb substrate has a porosity of 50 to 75%.

[7] The honeycomb structure according to any one of [1] to [5], wherein the honeycomb substrate has a porosity of 59 to 67%.

[8] Any one of [1] to [7] including a plugged portion that plugs an opening end portion on the inlet end face side of a predetermined cell and an opening end portion on the outlet end face side of the remaining cells. The honeycomb structure described.

  In the honeycomb structure of the present invention, a part of the coat layer penetrates into the pores of the outer peripheral wall, and the thickness of the invading part is specified within a predetermined range, so that the outer peripheral wall The pores are blocked. Therefore, even when a honeycomb substrate having a high porosity such that the porosity is 50% or more is used, when the catalyst slurry is introduced into the cell, the slurry does not ooze out to the outer surface of the outer peripheral wall. In the step of supporting the catalyst on the partition walls of the honeycomb structure, good workability can be obtained. Further, since the coat layer reinforces the outer peripheral wall, the strength of the outer peripheral wall is improved, and the outer peripheral wall is obtained when a part of the outer peripheral wall of the honeycomb structure is chucked (gripped) in the step of supporting the catalyst on the honeycomb structure. Can be effectively prevented. Furthermore, as a result of the improvement of the strength of the outer peripheral wall, the isostatic strength of the entire honeycomb structure is also improved, and damage during transportation and actual use of the honeycomb structure can be effectively prevented.

1 is a perspective view schematically showing an embodiment of a honeycomb structure of the present invention. 1 is a schematic diagram showing a cross section parallel to a cell extending direction of an embodiment of a honeycomb structure of the present invention. FIG. It is an enlarged view of the A section of FIG. It is a perspective view which shows typically other embodiment of the honeycomb structure of this invention. It is a schematic diagram which shows the cross section parallel to the cell extending direction of other embodiment of the honeycomb structure of this invention.

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

(1) Honeycomb structure:
FIG. 1 is a perspective view schematically showing one embodiment of a honeycomb structure of the present invention. FIG. 2 is a schematic view showing a cross section parallel to the cell extending direction of one embodiment of the honeycomb structure of the present invention, and FIG. 3 is an enlarged view of a portion A in FIG. As shown in FIGS. 1 and 2, the honeycomb structure 1 according to the present invention includes a honeycomb substrate 2 and a coat layer 3. The honeycomb substrate 2 is integrally formed with a porous partition wall 4 that partitions and forms a plurality of cells 5 extending from an inlet end surface 11 that is a fluid inlet side to an outlet end surface 12 that is a fluid outlet side. And a porous outer peripheral wall 6. Here, “integrally formed” means that the partition walls 4 and the outer peripheral wall 6 are simultaneously extruded in the manufacturing process of the honeycomb substrate 2, and in the obtained molded body, the partition walls 4 and the outer peripheral wall 6 Means that it was integrated immediately after extrusion. In the honeycomb substrate 2 obtained by firing such a molded body, the whole porosity, that is, the porosity of the partition walls 4 and the porosity of the outer peripheral wall 6 are the same.

  The coat layer 3 is disposed on at least a part of the outer surface of the outer peripheral wall 6 of the honeycomb substrate 2. The coat layer 3 includes a material that can enter the pores of the outer peripheral wall 6. Specifically, it is preferable to include particles having an average particle size smaller than the average pore size of the outer peripheral wall 6 and a water repellent material. The material of the particles is not particularly limited, but inorganic particles such as silicon carbide, silica, silicon nitride, cordierite, alumina, mullite, and zirconia are preferable, and particles containing Si (silicon) such as silicon carbide and silica are preferable. Particularly preferred. Also, the type of water repellent material is not particularly limited, but a material containing Si such as a silicone water repellent material is preferable. Specific examples of the silicone-based water repellent material include silicone oil.

  As shown in FIG. 3, in the present invention, a part of the coat layer 3 penetrates into the pores 7 of the outer peripheral wall 6. FIG. 3 shows an embodiment in which a coat layer 3 including particles 8 having an average particle diameter smaller than the average pore diameter of the outer peripheral wall 6 is disposed on the outer surface of the outer peripheral wall 6 of the honeycomb substrate 2. In this embodiment, the particles 8 included in the coat layer 3 are in a state of entering the pores 7 of the outer peripheral wall 6.

  As described above, in the present invention, a part of the coat layer 3 penetrates into the pores 7 of the outer peripheral wall 6, thereby closing the pores 7 of the outer peripheral wall 6. Therefore, since the catalyst is supported on the partition walls 4 of the honeycomb structure 1 of the present invention, even if the catalyst slurry is introduced into the cell 5, the slurry does not ooze out to the outer surface of the outer peripheral wall 6, and the honeycomb structure In the process of supporting the catalyst on the partition walls 4 of the body 1, good workability can be obtained. Further, since the coat layer 3 reinforces the outer peripheral wall 6, the strength of the outer peripheral wall 6 is improved, and a part of the outer peripheral wall 6 of the honeycomb structure 1 is chucked (gripped) in the step of supporting the catalyst on the honeycomb structure 1. ) Can be effectively prevented from being damaged. Furthermore, as a result of the improvement of the strength of the outer peripheral wall 6, the isostatic strength of the entire honeycomb structure 1 is also improved, and breakage of the honeycomb structure 1 during transportation and actual use can be effectively prevented. When the coating layer containing the water repellent material is disposed, the water repellent material in the coating layer is added to the catalyst slurry in addition to the effect of preventing the catalyst slurry from seeping out due to the pores of the outer peripheral wall being blocked. The effect of preventing seepage of the catalyst slurry by repelling can also be obtained.

  In the present invention, the thickness T2 of the portion 3b of the coat layer 3 that penetrates into the pores 7 of the outer peripheral wall 6 (hereinafter referred to as “intrusion portion”) is the thickness of the outer peripheral wall 6 of the honeycomb substrate 2. It is 1 to 90% of the thickness T1, preferably 10 to 60%, particularly preferably 15 to 50% (see FIG. 3). When the thickness T2 of the intrusion portion 3b of the coat layer 3 is 1 to 90% of the thickness T1 of the outer peripheral wall 6, the honeycomb substrate 2 having a high porosity such that the porosity is 50% or more is used. In addition, the pores 7 of the outer peripheral wall 6 can be effectively blocked. On the other hand, when the thickness T2 of the intruding portion 3b of the coat layer 3 is less than 1% of the thickness T1 of the outer peripheral wall 6, the honeycomb substrate 2 having a high porosity such that the porosity is 50% or more is used. In such a case, the clogging of the pores 7 of the outer peripheral wall 6 may be incomplete, and the effect of preventing the catalyst slurry from exuding may not be obtained. Further, when the thickness T2 of the penetration portion 3b of the coat layer 3 exceeds 90% of the thickness T1 of the outer peripheral wall 6, the coat layer 3 penetrates into the pores of the partition walls 4 and There is a possibility that the catalyst is not supported on the exhaust gas and the exhaust gas purification performance is deteriorated. In addition, the thickness of the penetration part 3b of the coating layer 3 was observed and measured by SEM (scanning electron microscope).

  In the present invention, the thickness T3 of the portion 3a of the coat layer 3 excluding the portion penetrating into the pores 7 of the outer peripheral wall 6 (hereinafter referred to as “non-intruding portion”) is 70 μm or less. And more preferably 8 μm or less (see FIG. 3). If the thickness T3 of the non-intruding portion 3a of the coat layer 3 exceeds 70 μm, the coat layer 3 may crack. The lower limit of the thickness T3 of the non-intruding portion 3a of the coat layer 3 is not particularly limited, but it is preferable to set the lower limit to about 5 μm in consideration of ease of manufacture. In addition, the thickness of the non-intrusion part 3a of the coat layer 3 was observed and measured by SEM (scanning electron microscope).

  In the present invention, the coat layer 3 may be disposed on the entire outer surface of the outer peripheral wall 6 of the honeycomb substrate 2 or may be disposed on a part thereof. For example, in the embodiment shown in FIG. 1 and FIG. 2, a portion of the outer surface of the outer peripheral wall 6 of the honeycomb substrate 2 excluding the vicinity of both end surfaces (inlet end surface 11 and outlet end surface 12) of the honeycomb substrate 2. Further, the coat layer 3 is disposed in a strip shape. This is an embodiment assuming that the catalyst is supported on the honeycomb structure 1 in a state in which the vicinity of both end faces of the honeycomb substrate 2 is chucked (gripped). That is, when the catalyst slurry is introduced into the cell 5 in such a state, the catalyst slurry does not ooze out from the chucked portion of the outer surface of the outer peripheral wall 6 of the honeycomb substrate 2. Even if the coat layer 3 is not disposed on the surface, the workability in the catalyst supporting process is not deteriorated.

Coat layer 3 preferably contains Si (silicon). In this case, Si may be contained in the coat layer in the form of particles such as SiC particles or SiO ₂ particles, or contained in the coat layer as a component of a water repellent material such as a silicone-based water repellent material. May be. By containing Si in the coat layer 3, the effect of preventing the catalyst slurry from exuding is improved. The amount of Si contained in the coat layer 3 is preferably 10 to 30% by mass of the entire coat layer 3. If the amount of Si contained in the coat layer 3 is less than 10% by mass of the entire coat layer 3, the effect of improving the effect of preventing the catalyst slurry from exuding may not be sufficiently exhibited. If the amount of Si contained in the coat layer 3 is more than 30% by mass of the entire coat layer 3, the thermal shock resistance of the coat layer 3 may be lowered.

  The coat layer 3 preferably further contains Ti (titanium). In order for the honeycomb structure to facilitate product management, information such as dimensions and mass may be displayed on the outer peripheral surface as a barcode or the like. Here, as a method for displaying information, a method of irradiating the outer peripheral surface of the honeycomb structure with laser light (laser marking) is widely used. In this case, when the surface of the material containing Ti is irradiated with laser light, the irradiated portion is colored black. For this reason, when information is displayed on the surface of the coating layer containing Ti by irradiating laser light, information can be displayed with high contrast, and the reading rate when reading information with a barcode reader or the like is improved. . The amount of Ti contained in the coat layer 3 is preferably 10 to 30% by mass of the entire coat layer 3. When the amount of Ti contained in the coat layer 3 is less than 10% by mass of the entire coat layer 3, when information is displayed (printed) by laser marking, the print becomes thin (the portion irradiated with the laser light is sufficient) In some cases, the effect of improving the reading rate of information is not sufficiently exhibited. On the other hand, if the amount of Ti contained in the coat layer 3 is more than 30% by mass of the entire coat layer 3, the thickness T2 of the intrusion portion 3b is increased, and the coatability may be deteriorated.

  The problem of the catalyst slurry seeping out to the outer surface of the outer peripheral wall and the problem of insufficient strength are particularly noticeable in a honeycomb structure having a high porosity such that the porosity is 50% or more. Therefore, the present invention is highly useful when a honeycomb substrate having a porosity of 50 to 75% is used, and is particularly useful when a honeycomb substrate having a porosity of 59 to 67% is used. The “porosity” mentioned here is a value measured by a mercury porosimeter. A typical use of such a high-porosity honeycomb structure is a type of GPF that supports and uses a catalyst. Therefore, the honeycomb structure of the present invention can be particularly preferably used for such a GPF. However, the honeycomb structure of the present invention is not limited to such a GPF, and can be widely used for various filters, catalyst carriers, and the like.

  The material of the honeycomb substrate 2 is preferably a ceramic material such as silicon carbide, silicon-silicon carbide based composite material, cordierite, mullite, alumina, spinel, silicon carbide-cordierite based composite material, lithium aluminum silicate, and aluminum titanate. . Among these, cordierite is particularly preferable. This is because when the material of the honeycomb substrate 2 is cordierite, a honeycomb structure having a small thermal expansion coefficient and excellent thermal shock resistance can be obtained.

  The average pore diameter of the honeycomb substrate 2 (the partition walls 4 and the outer peripheral wall 6) is preferably 10 to 30 μm, and particularly preferably 15 to 25 μm. If the average pore diameter of the honeycomb substrate 2 is less than 10 μm, the pressure loss of the honeycomb structure 1 becomes too high, and when used as a GPF, the engine output may be reduced. Further, when the average pore diameter of the honeycomb substrate 2 exceeds 30 μm, sufficient strength may not be obtained. Here, the “average pore diameter” is a value measured by a mercury porosimeter.

  The thickness of the partition walls 4 of the honeycomb substrate 2 is preferably 150 to 350 μm, and particularly preferably 200 to 310 μm. When the thickness of the partition wall 4 is less than 150 μm, sufficient strength may not be obtained. Moreover, when the thickness of the partition wall 4 exceeds 350 μm, the pressure loss of the honeycomb structure 1 becomes too high, and when used as a GPF, the engine output may be reduced.

  The thickness of the outer peripheral wall 6 of the honeycomb substrate 2 is preferably 300 to 1000 μm, and particularly preferably 500 to 800 μm. If the thickness of the outer peripheral wall 6 is less than 300 μm, sufficient strength may not be obtained. Moreover, when the thickness of the outer peripheral wall 6 exceeds 1000 μm, the pressure loss of the honeycomb structure 1 becomes too high, and when used as a GPF, the engine output may be reduced.

The cell density of the honeycomb substrate 2 is preferably 232.5 to 620.0 cells / cm ^2, and particularly preferably from 310.0 to 465.0 cells / cm ^2. When the cell density is less than 232.5 cells / cm ² , when used as a GPF, the effective area as a filter is insufficient, the pressure loss after PM deposition increases, and the engine output decreases. is there. Further, when the cell density exceeds 620.0 cells / cm ² , the pressure loss becomes too high, and when used as a GPF, the engine output may be reduced.

  The shape (outer shape) of the honeycomb substrate 2 is not particularly limited, and may be, for example, a cylindrical shape, an elliptical column shape, a polygonal column shape, or the like. Further, the shape of the cell 5 in a cross section perpendicular to the length direction of the honeycomb substrate 2 (hereinafter referred to as “cell shape”) is not particularly limited, but may be a polygon such as a quadrangle, a hexagon, an octagon or the like. For example, a combination of a square and an octagon is preferable.

  When the honeycomb structure 1 of the present invention is used for a PM collection filter such as GPF, as shown in FIGS. 4 and 5, the opening end portion of the predetermined cell 5a on the inlet end face 11 side and the remaining cells 5b It is preferable to form a plugging portion 9 that plugs the opening end on the outlet end face 12 side. Thus, by plugging one open end of each cell 5 of the honeycomb substrate 2 with the plugging portion 9, the honeycomb structure 1 has a wall flow type having high PM collection efficiency. It becomes a filter. In this wall flow type filter, the exhaust gas flowing into the cell 5 from the inlet end face 11 passes through the partition wall 4 and then flows out of the cell 5 from the outlet end face 12. And when exhaust gas permeate | transmits the partition 4, the partition 4 functions as a filtration layer, and PM contained in exhaust gas is collected. The plugged portion 9 has an inlet end surface 11 and an outlet end surface 12 each having a cell 5 whose open end is plugged by the plugged portion 9 and an open end by the plugged portion 9. It is preferable that the cells 5 not plugged are formed so as to have a checkered pattern.

  The material of the plugging portion 9 is preferably a material that is preferable as the material of the honeycomb substrate 2. The material of the plugging portion 9 and the material of the honeycomb substrate 2 may be the same material or different materials.

  The honeycomb structure 1 of the present invention is assumed to be used with a catalyst supported on the partition walls 4 of the honeycomb substrate 2. Here, the type of the catalyst supported on the partition walls 4 of the honeycomb substrate 2 is not particularly limited. For example, when used for automobile exhaust gas purification, it is preferable to use a noble metal. As the noble metal, platinum, rhodium or palladium, or a combination thereof is preferable. The amount of these noble metals supported is preferably 0.3 to 3.5 g / L per unit volume of the honeycomb structure 1.

  Since the catalyst such as a noble metal is supported on the partition walls 4 in a highly dispersed state, the catalyst may be previously supported on a heat-resistant inorganic oxide having a large specific surface area such as alumina and then supported on the partition walls 4 of the honeycomb substrate 2. preferable. In addition to alumina, as the heat-resistant inorganic oxide for supporting the catalyst, zeolite or the like can be used depending on the application. A catalyst such as a noble metal may be supported on the partition walls 4 of the honeycomb substrate 2 after being fixed to a promoter made of ceria, zirconia, or a composite oxide thereof.

  In the honeycomb structured body of the present invention, the outer peripheral wall of the honeycomb base material is not formed integrally with the partition walls, but may be formed separately from the partition walls. Here, “formed separately from the partition walls” means that the formation of the peripheral wall of the honeycomb substrate was performed after the formation of the partition walls in the honeycomb substrate manufacturing process. means. As described above, even when the catalyst is supported on the partition walls of the honeycomb structure in which the partition walls and the outer peripheral wall are separately formed, the catalyst slurry introduced into the cell when the porosity of the outer peripheral wall is 35% or more May ooze out to the outer surface of the outer peripheral wall. However, when a predetermined coat layer is disposed as in the present invention, the outer peripheral wall of the honeycomb base material constituting the honeycomb structure is formed separately from the partition walls, and the outer peripheral wall of the outer peripheral wall is formed. Even when the porosity is 35% or more, exudation of the catalyst slurry can be effectively prevented.

  When the outer peripheral wall of the honeycomb base material is formed separately from the partition walls, the porosity of the outer peripheral wall and the porosity of the partition walls may be the same or different. In this case, the average pore diameter of the outer peripheral wall and the average pore diameter of the partition walls may be the same or different. Further, in this case, the material of the outer peripheral wall and the material of the partition wall may be the same or different. The “porosity” and “average pore diameter” mentioned here are values measured by a mercury porosimeter.

(2) Manufacturing method of honeycomb structure:
An example of a method for manufacturing a honeycomb structure according to the present invention will be described. First, in order to produce a honeycomb substrate, a forming raw material containing a ceramic raw material is produced. The ceramic raw material is at least one selected from the group consisting of silicon carbide, silicon-silicon carbide based composite material, cordierite forming raw material, mullite, alumina, spinel, silicon carbide-cordierite based composite material, lithium aluminum silicate and aluminum titanate. Preferably it is a seed. Among these, a cordierite-forming raw material having a small thermal expansion coefficient and excellent thermal shock resistance is preferable. The cordierite forming raw material is a ceramic raw material blended so as to have a chemical composition that falls within the range of 42 to 56 mass% silica, 30 to 45 mass% alumina, and 12 to 16 mass% magnesia. The cordierite forming raw material becomes cordierite by being fired.

  The forming raw material is preferably prepared by mixing the ceramic raw material as described above with a dispersion medium, an organic binder, an inorganic binder, a pore former, a surfactant and the like. The composition ratio of each raw material is not particularly limited, and is preferably a composition ratio according to the structure, material, and the like of the honeycomb base material to be manufactured.

  Next, the forming raw material is kneaded to form a clay. There is no particular limitation on the method of kneading the forming raw material to form the clay. Suitable methods include, for example, a method using a kneader, a vacuum kneader or the like.

  Next, a honeycomb formed body in which the partition walls and the outer peripheral wall are integrated is extruded from the clay using the die having the lattice-shaped slits, and the honeycomb formed body is dried. The drying method is not particularly limited. Suitable drying methods include, for example, hot air drying, microwave drying, dielectric drying, reduced pressure drying, vacuum drying, freeze drying and the like. Among these, dielectric drying, microwave drying, and hot air drying are preferably performed alone or in combination.

  Subsequently, the dried honeycomb formed body (honeycomb dried body) is fired to produce a honeycomb substrate. In addition, before this firing (main firing), it is preferable to perform calcination (degreasing) in order to remove the binder and the like contained in the honeycomb formed body. The conditions for the calcination are not particularly limited as long as the organic substances (organic binder, surfactant, pore former, etc.) contained in the honeycomb formed body can be removed. Generally, the combustion temperature of the organic binder is about 100 to 300 ° C., and the combustion temperature of the pore former is about 200 to 800 ° C. Therefore, it is preferable to heat at about 200 to 1000 ° C. for about 3 to 100 hours in an oxidizing atmosphere as a condition for calcination. Since the conditions (temperature, time, atmosphere, etc.) for firing (main firing) the honeycomb formed body vary depending on the type of the forming raw material, an appropriate condition may be selected according to the type. For example, when a cordierite forming raw material is used, the firing temperature is preferably 1410 to 1440 ° C. Moreover, it is preferable that baking time shall be about 4 to 8 hours as keep time in the highest temperature. The apparatus which performs calcination and main baking is not specifically limited. As a suitable apparatus, an electric furnace, a gas furnace, etc. can be mentioned, for example.

  When a honeycomb structure having a plugged portion is manufactured, the plugged portion is formed on the honeycomb substrate. The plugging portion is formed so as to plug the opening end on the one end face (inlet end face) side of the predetermined cell and the opening end on the other end face (outlet end face) side of the remaining cells. A conventionally known method can be used for forming the plugged portion. As an example of a specific method, first, a sheet is attached to the end face of the honeycomb substrate manufactured by the method as described above. Next, a hole is made in the sheet at a position corresponding to the cell in which the plugging portion is to be formed. Next, with the sheet attached, the end face of the honeycomb substrate is immersed in a plugging slurry in which the plugging portion forming material is slurried, and the plugging is made through the holes formed in the sheet. The plugging slurry is filled into the open end of the cell to be stopped. The plugging slurry thus filled is dried and then fired and cured to form a plugged portion. It is preferable to use the same material as the material for forming the honeycomb base material as the material for forming the plugged portions. The plugging portion may be formed at any stage after the honeycomb formed body is dried, after calcining, or after firing (main firing).

  Next, a slurry for forming a coat layer containing particles having an average particle size smaller than the average pore size of the outer peripheral wall of the honeycomb substrate thus prepared is prepared. The particles to be contained in the slurry for forming the coating layer are preferably inorganic particles such as silicon carbide, silica, silicon nitride, cordierite, alumina, mullite, zirconia, and particularly preferably particles containing Si such as silicon carbide and silica. The slurry for forming the coat layer preferably contains a binder capable of binding the particles to the inner surface of the fine pores of the outer peripheral wall in addition to such particles, and these are diluted with water. You may include a dispersing agent and an antifoamer suitably. As the binder, colloidal sols such as silica sol and alumina sol, and lamellar compounds which swell and exhibit binding properties can be suitably used.

  Such a coating layer forming slurry is applied to the outer surface of the outer peripheral wall of the honeycomb substrate and dried to dispose the coating layer. In applying the coating layer forming slurry, a part of the slurry enters the pores of the outer peripheral wall, and the thickness of the intruding portion is 1 to 90% of the thickness of the outer peripheral wall. To control. For example, when the coating layer forming slurry is applied using a roller, the above-described control can be performed by the pressure pressing the roller against the outer peripheral wall, the number of rotations of the roller, or the like. Instead of the slurry for forming the coating layer, a water-repellent material may be applied to the outer surface of the outer peripheral wall of the honeycomb substrate, and a coating treatment may be performed by heating, light irradiation, or the like. In this case, as the water repellent material, a material containing Si such as a silicone water repellent material is preferable. Further, when the coat layer is disposed on a part of the outer surface of the outer peripheral wall, the portion of the outer surface of the outer peripheral wall that is not formed with the coat layer is masked with a tape or the like, and then the slurry for forming the coat layer or It is preferable to apply a water material.

  Thus, the honeycomb structure of the present invention can be obtained by forming the coat layer on the outer surface of the outer peripheral wall of the honeycomb substrate. When the catalyst is supported on the honeycomb structure of the present invention, a catalyst slurry containing a catalyst such as a noble metal is attached to the surfaces of the partition walls and pores using a conventionally known catalyst supporting method such as a suction method, It is preferable that the catalyst contained in the catalyst slurry is baked on the partition walls by performing a high temperature treatment.

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

(Examples 1-20 and Comparative Examples 1 and 2)
A pore former, a binder, a surfactant, and water are added to a cordierite-forming raw material mainly composed of talc, kaolin, and alumina to produce a forming raw material, which is kneaded with a vacuum kneader to form a clay. Got. Starch was used as the pore former. Moreover, methylcellulose and hydroxypropoxymethylcellulose were used as the binder. As the surfactant, sodium laurate was used. The addition amount of each raw material was 5 parts by mass of the pore former, 3 parts by mass of methyl cellulose, 3 parts by mass of hydroxypropoxymethyl cellulose, 1 part by mass of surfactant, and 32 parts by mass of water with respect to 100 parts by mass of the cordierite forming raw material. .

  The obtained clay is extruded using a die for forming a honeycomb molded body, and a partition wall that partitions and forms a plurality of cells extending from an inlet end surface serving as a fluid inlet side to an outlet end surface serving as a fluid outlet side, and A columnar honeycomb formed body having a partition wall and an outer peripheral wall formed integrally was obtained. Thereafter, these honeycomb formed bodies were dried with microwaves and hot air to obtain dried honeycomb bodies.

  Next, plugged portions were formed at one open end of each cell of the dried honeycomb body. The plugged portion is formed by a cell in which the plugged portion is formed at the open end and a cell in which the plugged portion is not formed at the open end, and each end surface of the dry body has a checkered pattern. I went to present. As a method for forming the plugged portion, first, a sheet was attached to the end face of the dried body, and a hole was formed in the sheet at a position corresponding to the cell where the plugged portion is to be formed. Subsequently, with the sheet attached, the end face of the dried body is immersed in a plugging slurry in which the forming material of the plugging portion is slurried, and the plugging is made through a hole formed in the sheet. The plugging slurry was filled into the open end of the cell to be prepared. In addition, the same material as the molding raw material was used as a material for forming the plugging portion.

  Thus, after the plugging slurry filled in the open ends of the cells was dried, these dried honeycomb bodies were calcined (degreasing) at about 400 ° C. in an air atmosphere. Then, the honeycomb base material in which the outer peripheral wall was integrally formed with the partition walls was obtained by firing at about 1450 ° C. The obtained honeycomb substrate had a columnar shape with a diameter of 118.4 mm and a length of 127.0 mm, a cell shape of square, and the other structures were as shown in Table 1.

Subsequently, 25 parts by mass of TiO ₂ and 25 parts by mass of SiC were added to 50 parts by mass of colloidal silica particles having an average particle diameter of 0.002 μm, and stirred well to prepare a slurry for forming a coat layer. This slurry for forming a coating layer was applied in a strip shape to the portion of the outer surface of the outer peripheral wall of the honeycomb substrate except for the vicinity of both end faces of the honeycomb substrate. Thereafter, the honeycomb base material was dried, and a coating layer in which the thicknesses of the intrusion part and the non-intrusion part were values shown in Table 1 was disposed, and the honeycomb structures of Examples 1 to 20 and Comparative Examples 1 and 2 Got. The coating layer forming slurry was applied using a roller, and the thickness of the intrusion portion and the non-intrusion portion was controlled by the pressure with which the roller was pressed against the outer peripheral wall of the honeycomb substrate, the number of rotations of the roller, and the like.

(Examples 21 to 40 and Comparative Examples 3 and 4)
The clay obtained in the same manner as in Examples 1 to 20 and Comparative Examples 1 and 2 is extruded using a die for forming a honeycomb formed body, and the fluid is placed on the fluid outlet side from the fluid inlet side. A honeycomb formed body having partition walls for partitioning a plurality of cells extending to the outlet end face was obtained. Thereafter, these honeycomb formed bodies were dried with microwaves and hot air to obtain dried honeycomb bodies.

  Next, in one of the open ends of each cell of the dried honeycomb body, in the same manner as in Examples 1 to 20 and Comparative Examples 1 and 2, the plugging slurry was filled to form a plugged portion. . After the plugging slurry filled in the open ends of the cells was dried, these dried honeycomb bodies were calcined (degreasing) at about 400 ° C. in an air atmosphere. Thereafter, firing was performed at about 1450 ° C. to obtain a honeycomb fired body. Next, the outer periphery was ground so that the outer shape of the honeycomb fired body became a cylindrical shape. After grinding, an outer peripheral wall forming material made of the same material as the forming raw material is applied to the processed surface, dried and cured at 700 ° C. for 2 hours to form an outer peripheral wall, and the outer peripheral wall is formed separately from the partition wall. A honeycomb substrate was obtained. The obtained honeycomb substrate had a columnar shape with a diameter of 118.4 mm and a length of 127.0 mm, a cell shape of square, and the other structures were as shown in Table 2.

  Subsequently, the slurry for forming a coating layer obtained in the same manner as in Examples 1 to 20 and Comparative Examples 1 and 2 was applied to the vicinity of both end faces of the honeycomb substrate on the outer surface of the outer peripheral wall of the honeycomb substrate. It was applied in a strip shape on the part to be removed. Thereafter, the honeycomb base material was dried, and a coating layer in which the thicknesses of the intrusion portion and the non-intrusion portion had values shown in Table 2 was disposed, and the honeycomb structures of Examples 21 to 40 and Comparative Examples 3 and 4 Got. The coating layer forming slurry was applied using a roller, and the thickness of the intrusion portion and the non-intrusion portion was controlled by the pressure with which the roller was pressed against the outer peripheral wall of the honeycomb substrate, the number of rotations of the roller, and the like.

(Evaluation)
For the honeycomb structures of Examples 1 to 40 and Comparative Examples 1 to 4, the following methods were used to prevent the catalyst slurry from seeping out, the exhaust gas purification performance, the presence or absence of cracks in the coating layer, and the outer peripheral wall. The results are shown in Table 3 and Table 4.

[Prevention of catalyst slurry exudation]
After mixing 1200 parts by mass of Al ₂ O ₃ , 300 parts by mass of CeO ₂ , 1 part by mass of Pt and 15000 parts by mass of water, wet grinding was performed to prepare a catalyst slurry having a viscosity of about 2 mPa · s. With the vicinity of both end faces of the honeycomb structure (the part where the coating layer is not disposed) being chucked, the inlet end face of the honeycomb structure is immersed in the catalyst slurry and sucked from the outlet end face, and the catalyst is put into the cell. The slurry was introduced, and the catalyst slurry was adhered to the partition walls. Further, the honeycomb structure was turned upside down, the exit end face of the honeycomb structure was immersed in the catalyst slurry, sucked from the entrance end face, the catalyst slurry was introduced into the cell, and the catalyst slurry was adhered to the partition walls. Thus, it was examined whether or not the catalyst slurry exudes to the outer surface of the outer peripheral wall of the honeycomb structure when the catalyst slurry was introduced into the cell by suction. As a result, the catalyst slurry including the water contained in the catalyst slurry is “excellent” when the catalyst slurry is not exuded, and the case where only the water contained in the catalyst slurry is exuded is “good”. The case where Al ₂ O ₃ and CeO ₂ exude was regarded as “impossible”.

[Exhaust gas purification performance]
The catalyst slurry adhered to the partition walls of the honeycomb structure as described above was dried at 120 ° C. for 2 hours, and then heated at 550 ° C. for 1 hour to burn the catalyst contained in the catalyst slurry onto the partition walls. In addition, a honeycomb structure without a coating layer was produced in the same manner as in Examples 1 to 40 and Comparative Examples 1 to 4 except that no coating layer was provided, and the catalyst was separated from the partition wall in the same manner. Baked into. Thus, the honeycomb structures of Examples 1 to 40 and Comparative Examples 1 to 4 in which the coat layer was disposed, and equivalent to Examples 1 to 40 and Comparative Examples 1 to 4 except that the coat layer was not disposed. A catalyst was supported on each honeycomb structure. With respect to these honeycomb structures, the purification rate of NO _x contained in the exhaust gas when running in NEDC mode with a direct injection gasoline engine with a displacement of 1.4 L and stoichiometric combustion was measured. A case where the NO _x purification rate of the honeycomb structure provided with the coat layer is 90% or more of the NO _x purification rate of the honeycomb structure provided with no coat layer is defined as “excellent”. did. Further, the case where the NO _x purification rate of the honeycomb structure provided with the coat layer is less than 90% of the NO _x purification rate of the honeycomb structure provided with no coat layer is determined as “impossible”. did.

[Coating layer cracks]
The coat layer of the honeycomb structure was visually observed to check for cracks. And it was confirmed that the case where there was no crack in the coating layer was “excellent”, and that there was a crack in the coating layer, but the case where the crack did not progress to the honeycomb substrate was determined as “good”.

[Strength of outer wall]
For the honeycomb structures of Examples 1 to 40 and Comparative Examples 1 to 4, the strength of the outer peripheral wall before arranging the coat layer and the strength of the outer peripheral wall after arranging the coat layer were measured. The strength of the outer peripheral wall was measured by a method in which a spherical weight made of alumina was dropped perpendicularly to the outer peripheral wall of the honeycomb structure. Specifically, until the outer peripheral wall of the honeycomb structure is damaged due to the impact of the falling of the weight, the weight of the weight is changed by changing the weight and the falling distance, and the weight of the weight when the outer peripheral wall is damaged is repeated. The impact energy was calculated from the drop distance and the “outer wall strength”.

(Discussion)
The “strength of the outer peripheral wall” was higher in the honeycomb structures of Examples 1 to 40 and Comparative Examples 1 to 4 after the coating layer was disposed than before the coating layer was disposed. In addition, the honeycomb structures of Examples 1 to 40 had a “catalyst slurry seepage prevention effect” of “excellent” or “possible” and an “exhaust gas purification performance” of “excellent”. Although the honeycomb structures of Examples 14, 16, 18-20, and 33-36 had cracks in the coating layer, the “catalyst slurry exudation preventing effect” and the “exhaust gas purification performance” were both It was “excellent”. This is presumably because the cracks generated in the coating layer were so slight that they did not propagate to the honeycomb substrate. On the other hand, in the honeycomb structures of Comparative Examples 2 and 4 in which the thickness of the invading portion of the coat layer was less than 1% of the thickness of the outer peripheral wall, the “preventive effect of catalyst slurry exudation” was “impossible” . This is presumably because the penetration portion of the coating layer was too thin, and the pores in the outer peripheral wall were not completely blocked, and the catalyst slurry could not be sufficiently prevented from exuding. Further, the honeycomb structures of Comparative Examples 1 and 3 in which the thickness of the invading portion of the coat layer exceeded 90% of the thickness of the outer peripheral wall were “impossible” in “exhaust gas purification performance”. This is presumably because the intrusion portion of the coat layer was too thick, so that the coat layer penetrated into the pores of the partition walls, and the catalyst was not supported in the pores of the partition walls at the intrusion portions.

  The present invention can be suitably used for a filter for collecting particulate matter contained in exhaust gas from a diesel engine or a gasoline engine, such as a filter that needs to carry a catalyst.

1: honeycomb structure, 2: honeycomb substrate, 3: coat layer, 4: partition wall, 5: cell, 6: outer peripheral wall, 7: pore, 8: particle, 9: plugging portion, 11: inlet end face , 12: outlet end face.

Claims (8)

  A honeycomb having a porous partition wall defining a plurality of cells extending from an inlet end surface serving as a fluid inlet side to an outlet end surface serving as a fluid outlet side, and a porous outer peripheral wall integrally formed with the partition wall A coating layer disposed on at least a part of the outer surface of the base material and the outer peripheral wall, the coating layer partly penetrates into the pores of the outer peripheral wall; A honeycomb structure, wherein a thickness of a portion of the outer peripheral wall penetrating into the pores is 1 to 90% of a thickness of the outer peripheral wall.   A porous partition wall defining a plurality of cells extending from an inlet end surface serving as a fluid inlet side to an outlet end surface serving as a fluid outlet side, and a porous layer formed separately from the partition wall and having a porosity of 35% or more And a coat layer disposed on at least a part of the outer surface of the outer peripheral wall, and the coat layer partially penetrates into the pores of the outer peripheral wall. A honeycomb structure in which a thickness of a portion of the coat layer penetrating into the pores of the outer peripheral wall is 1 to 90% of a thickness of the outer peripheral wall.   The honeycomb structure according to claim 1 or 2, wherein a thickness of a portion of the coat layer excluding a portion penetrating into the pores of the outer peripheral wall is 70 µm or less.   The honeycomb structure according to any one of claims 1 to 3, wherein the coat layer contains Si.   The honeycomb structure according to claim 4, wherein the coat layer further contains Ti.   The honeycomb structure according to any one of claims 1 to 5, wherein the honeycomb substrate has a porosity of 50 to 75%.   The honeycomb structure according to any one of claims 1 to 5, wherein the honeycomb substrate has a porosity of 59 to 67%.   The honeycomb according to any one of claims 1 to 7, further comprising a plugging portion that plugs an opening end portion on the inlet end face side of a predetermined cell and an opening end portion on the outlet end face side of a remaining cell. Structure.

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