JP2005324154A - Ceramic honeycomb structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ceramic honeycomb structure having a very low-pressure-drop characteristic, high collection efficiency and mechanical strength to withstand mechanical vibrations and a mechanical or thermal shock during use, which is used for an exhaust gas cleaner to collect particulates contained in an exhaust gas from a diesel engine, and in which the exaust gas is passed through a porous partition wall parting gas passages by sealing predetermined gas passages of the ceramic honeycomb structure. <P>SOLUTION: An area ratio of 3 to 16% of a solid wall in a cross section of the partition wall of the ceramic honeycomb structure and a maximum size of 5 to 30 μm of the solid wall are attained by controlling a particle-size distribution of a raw material alumina powder in a raw material cordierite powder and optimizing a content of the raw material alumina powder therein. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a ceramic honeycomb structure suitable for use in a ceramic honeycomb filter for removing fine particles contained in exhaust gas of a diesel engine.

  In order to remove fine particles discharged from diesel engines, ceramic honeycomb filters for collecting fine particles having a structure in which the partition walls of the ceramic honeycomb structure have a porous structure and allow exhaust gas containing fine particles to pass through the partition walls have been used. ing. FIG. 1 shows a front view and a side view of the ceramic honeycomb filter. Regarding the characteristics of this ceramic honeycomb filter, three are important: pressure loss, particulate collection efficiency, and particulate collection time (time from the start of collection until reaching a certain pressure loss). Above all, the pressure loss and the collection efficiency are in a contradictory relationship. If you try to reduce the pressure loss, the collection time can be lengthened, but the collection efficiency deteriorates, and if you try to increase the collection efficiency, the pressure loss increases. The collection time is shortened. Therefore, in order to satisfy these contradictory filter characteristics, for the ceramic honeycomb structure, as shown below, the porosity of the partition walls, the average pore diameter, the pore distribution, the pores existing on the partition wall surface, Techniques for controlling the size, the surface roughness of the partition wall surface, and the like have been studied conventionally.

  In the invention described in Patent Document 1, among the cordierite-forming raw material powders, the pore diameter obtained by a production method for adjusting the particle size and content of kaolin, talc, silica, aluminum oxide, and aluminum hydroxide The pore volume of less than 10 μm is 15% or less of the total pore volume, the pore volume having a pore diameter of 10 to 50 μm is 75% or more of the total pore volume, and the pore volume exceeding 50 μm is the total pore volume. No. 10% or less and a porosity of 50 to 80% is disclosed. According to the present invention, it is possible to obtain a filter that has a high particulate collection efficiency and can prevent an increase in pressure loss due to pore clogging.

  In the invention described in Patent Document 2, the porosity is 55 to 65%, and the average pore diameter is obtained by a production method of adjusting the amount of graphite and synthetic resin added to the cordierite forming raw material. A honeycomb ceramic structure having a size of 15 to 30 μm and having a total area of pores exposed on the partition wall surface constituting the honeycomb structure is 35% or more of the total area of the partition wall surface is disclosed. According to the present invention, a filter capable of achieving low pressure loss and high collection efficiency can be obtained.

  In addition, in the invention described in Patent Document 3, kaolin and aluminum oxide are not included in the cordierite forming raw material, talc powder having an average particle size of 30 to 200 μm, fused silica powder having an average particle size of 30 to 200 μm, and an average particle size of A porosity of 55 to 80% and an average pore diameter obtained by a production method using a raw material obtained by adding a predetermined organic foaming agent or a combustible substance to a cordierite forming raw material comprising a mixture of 5 to 20 μm aluminum hydroxide powder A honeycomb structure having a pore volume of 30 to 50 μm and a pore volume of 100 μm or more being 0.05 or less of the total pore volume is disclosed. According to the present invention, a honeycomb filter having characteristics of a high collection rate, a low pressure loss, and a low thermal expansion coefficient can be provided.

In the invention described in Patent Document 4, the average particle diameter of talc and silica as the pore-forming raw material satisfies the relationship of (2 × average particle diameter of silica) ≧ (average particle diameter of talc), and the average particle of talc By using a raw material system having a diameter of 40 μm or less and an average particle diameter of silica of 80 μm or less, the porosity is 45% or more and 60% or less, and the pore volume of 100 μm or more is 10% of the total pore volume. %, And the relationship between the specific surface area M (m ² / g) of all pores opening and penetrating from the surface toward the inside and the surface roughness N (μm) on the filter surface is 1000 M + 85 N ≧ 530 A range of porous ceramic honeycomb filters is disclosed. According to the present invention, it is said that a porous ceramic honeycomb filter having a long collection time and a small number of regenerations can be obtained.

JP 2002-219319 A JP 2003-40687 A JP 2002-357114 A Japanese Patent No. 2726616

However, in a ceramic honeycomb filter in which a catalytic substance is supported on the surface of the partition walls of the ceramic honeycomb filter or in the pores in the partition walls, which has recently been studied for adoption, fine particles are collected on the ceramic honeycomb filter. On the other hand, in order to burn fine particles by the action of the catalytic substance, it has been desired to develop a ceramic honeycomb filter in which the fine structure inside the partition walls is controlled more than in the prior art. Furthermore, an exhaust gas purification device having a structure in which a honeycomb structure carrying an oxidation catalyst is arranged upstream of the exhaust gas passage of this ceramic honeycomb filter has been studied, so that the pressure loss of the entire device does not increase. Therefore, the appearance of a ceramic honeycomb filter having a lower pressure loss characteristic than before has been demanded. Further, in the exhaust gas regulations that will continue to be strengthened in the future, the demand for reducing particulates and NOx in the exhaust gas will become stronger than ever. Therefore, the ceramic honeycomb structure in which the above oxidation catalyst is supported in the exhaust gas passage. body, in addition to the ceramic honeycomb filter, the catalyst exhaust gas purification device arranged ceramic honeycomb structure supporting for of the NO _X reduction has also been studied, for the ceramic honeycomb filter, smooth combustion of the particulates Honeycomb filter that has low pressure loss characteristics over the prior art, has a sufficiently high particulate collection efficiency, and has a strength that can withstand mechanical vibration, impact, or thermal shock during use. Was long-awaited.

  In response to such demands for low pressure loss, high collection efficiency, and high strength, the honeycomb structure and the honeycomb filter described in Patent Documents 1 to 4 which are the conventional technologies described above have partition walls. Pay attention to the size and amount of pores inside and on the partition walls, such as the porosity, average pore diameter, pore distribution inside the partition walls, and the size and area ratio of pores opened on the partition surface. However, no consideration has been given to the structure inside the partition, that is, the partition component. For this reason, it can be applied to exhaust gas purification equipment that can meet exhaust gas regulations that will be strengthened in the future, with low pressure loss and high collection efficiency, and sufficient strength to withstand mechanical vibration, shock or thermal shock during use. There was a problem that a honeycomb filter satisfying the above conditions could not be obtained. The present invention solves the above-mentioned problems, and is suitable for application to a ceramic honeycomb filter satisfying low pressure loss, high collection efficiency, and sufficient strength to withstand mechanical vibration, shock or thermal shock during use. An object is to provide a honeycomb structure.

  In order to solve the above-mentioned problems, the present inventor has intensively studied, and as a result, by optimizing the partition wall constituting part of the ceramic honeycomb structure, it has a high pressure response characteristic, particularly an advanced exhaust gas regulation that can meet future exhaust gas regulations. Applicable to ceramic honeycomb filters that have low pressure loss characteristics suitable for use in exhaust gas purification equipment, high collection efficiency, and strength characteristics that can withstand mechanical vibration, shock, or thermal shock during use. The present inventors have found that a ceramic honeycomb structure can be obtained, and have arrived at the present invention.

  That is, the ceramic honeycomb structure of the present invention plugs a predetermined flow path of the ceramic honeycomb structure made of a material having cordierite as a main crystal, and exhaust gas is passed through the porous partition walls that define the flow path. A ceramic honeycomb structure used for a ceramic honeycomb filter that removes fine particles contained in exhaust gas by allowing it to pass through, wherein an area ratio of partition wall constituent portions in a fracture surface of the partition wall is 3 to 16%, The average value of the maximum dimension of the partition wall constituting portion is 5 to 30 μm.

In the ceramic honeycomb structure of the present invention, the total pore volume of the partition walls is 0.60 to 1.00 cm ³ / g, and the pore distribution of the partition walls is a pore volume having a pore diameter of 2 μm or more: 0.60 -0.95 cm ³ / g, pore volume of 5 μm or more: 0.60 to 0.95 cm ³ / g, pore volume of 10 μm or more: 0.50 to 0.90 cm ³ / g, pore volume of 20 μm or more : 0.35~0.70cm ³ / g, 40μm or more pore volume: 0.10~0.35cm ³ / g, 100μm or more pore volume: it is preferably 0.07cm at ³ / g or less.

  The effects of the present invention will be described. The ceramic honeycomb structure of the present invention plugs a predetermined flow path of a ceramic honeycomb structure made of a material having cordierite as a main crystal, and allows exhaust gas to pass through porous partition walls that define the flow path. Thus, a ceramic honeycomb structure used for a ceramic honeycomb filter for removing fine particles contained in exhaust gas, wherein an area ratio of partition wall constituent portions in a fracture surface of the partition wall is 3 to 16%, and the partition wall The average value of the maximum dimensions of the constituent parts is 5 to 30 μm. Here, the fracture surface of the partition wall refers to a fracture surface obtained from an SEM image obtained by observing the fracture surface of the partition wall from a direction along the partition wall with a scanning electron microscope (abbreviated as SEM). The constituent part refers to a ceramic part constituting the partition wall in the fracture surface obtained from the SEM image. Further, the maximum dimension of the partition wall constituent portion means the largest diameter among the diameters passing through the center of gravity of the partition wall constituent portion and connecting two points on the outer periphery of the partition wall constituent portion in the fracture surface obtained from the SEM image.

  As described above, the average area ratio and maximum dimension of the partition wall components in the partition wall fracture surface of the ceramic honeycomb structure are within an appropriate range, so low pressure loss, high collection efficiency, and high strength characteristics that can withstand practical use Thus, a ceramic honeycomb filter satisfying the conflicting characteristics can be obtained. That is, when the exhaust gas passes through the partition wall, the partition wall component becomes a substantial resistance to the exhaust gas flow, and bears the stress applied to the filter. And the size is important in achieving both the pressure loss characteristics, the collection efficiency, and the strength conflicting characteristics of the filter with respect to the exhaust gas containing fine particles. This is because a ceramic honeycomb structure having a low pressure loss, a high collection efficiency, and a high strength can be obtained by setting the average value of the maximum dimension of the partition wall constituting part to 16% and 5 to 30 μm.

  Here, it is important to define the area ratio and the size of the partition wall constituting portion in the fracture surface of the partition wall not by the cut surface of the partition wall but by the fracture surface. The reason for this will be described with reference to FIG. 4 for easy understanding. When observing the cut surface obtained by cutting the partition wall along A, the ratio of the partition wall components appearing on the cut surface merely represents the magnitude of the porosity. On the other hand, when the partition wall is broken, for example, along B, the fracture surface is formed along the pores communicating with each other or through the weakest part of the partition component part. By defining the area ratio and dimensions of the portion, it becomes possible to more appropriately represent the influence of the partition wall component on the pressure loss, the collection efficiency, and the strength.

  Here, in the fracture surface of the partition wall, the area ratio of the partition wall constituent portion is limited to 3 to 16% and the maximum dimension of the partition wall constituent portion is numerically limited to 5 to 30 μm for the following reason. If the area ratio of the partition wall component exceeds 16%, the degree of pore communication will deteriorate, the resistance of the partition wall component to the exhaust gas flow will increase, the pressure loss will increase, and the area ratio of the partition wall component will be 3%. If it is less than the range, the ratio of the partition wall constituent parts is reduced, so that the collection efficiency and strength are lowered. Moreover, in the fracture surface of the partition wall, if the average value of the maximum dimension of the partition wall component exceeds 30 μm, the resistance to the exhaust gas flow increases and the pressure loss increases, and the average value of the maximum dimension of the partition wall component is less than 5 μm. If it exists, the dimension of a partition structural part will become small and collection efficiency and intensity | strength will fall. From the above viewpoint, the area ratio of the partition wall constituent part is more preferably 3 to 8%, and the average value of the maximum dimension of the more preferable partition wall constituent part is 10 to 20 μm.

  Here, in the fracture surface of the partition wall, the area ratio of the partition wall constituent portions and the average value of the maximum dimensions were measured as follows. First, the fracture surface of an arbitrary partition wall is observed with an SEM, a field of view of 0.8 × 0.8 mm is selected, a photograph is taken, the inside of the photographed field of view is further increased (250 to 10000 times), and brittleness is observed. The portion that was the fracture surface was regarded as a partition wall component, blacked on the photo and binarized, and then image analysis was performed on the black painted part to determine the area ratio and maximum dimension of the partition wall component. . An example after binarizing the fracture surface of the partition wall is shown in FIG. In addition, although the measurement of the area rate of a partition component part was performed several times, changing the observation location of SEM observation, and it calculated | required as an average value, it is preferable to carry out at least 10 or more places.

In the ceramic honeycomb structure of the present invention, the total pore volume of the partition walls is 0.60 to 1.00 cm ³ / g, and the pore distribution of the partition walls is a pore volume having a pore diameter of 2 μm or more: 0.60 -0.95 cm ³ / g, pore volume of 5 μm or more: 0.60 to 0.95 cm ³ / g, pore volume of 10 μm or more: 0.50 to 0.90 cm ³ / g, pore volume of 20 μm or more : 0.35~0.70cm ³ / g, 40μm or more pore volume: 0.10~0.35cm ³ / g, 100μm or more pore volume: the is preferably 0.07cm at ³ / g or less Is 3 to 16% of the area ratio of the partition wall constituent part in the fracture surface of the partition wall, the average value of the maximum dimension of the partition wall constituent part is 5 to 30 μm, and the total pore volume of the partition wall is 0.60. as ~1.00cm ³ / g, and in the partition wall By containing pores having a pore diameter of 2 μm or less to pores of 100 μm or more in a desired ratio, pores of various sizes communicate with each other, the communication ratio between the pores increases, and it is more reliably reduced. This is because the pressure loss characteristics, high collection rate, and high strength can be achieved at the same time.

  Here, a preferable range of the pore distribution of the partition walls in the ceramic honeycomb structure of the present invention will be described with reference to FIG. FIG. 3 is a graph showing the relationship between the pore diameter and the cumulative pore volume. Point (12) indicates the upper limit of the preferred total pore volume of the present invention, and point (11) indicates the preferred total of the present invention. The lower limit of the pore volume is shown, and the point □ (14) shows the upper limit of the preferred cumulative pore volume at the pore diameter of 2 μm or more, 5 μm or more, 10 μm or more, 20 μm or more, 40 μm or more, 100 μm or more of the present invention. (13) shows a preferable lower limit of the cumulative pore volume of the present invention when the pore diameter is 2 μm or more, 5 μm or more, 10 μm or more, 20 μm or more, 40 μm or more, 100 μm or more. Further, point (15) indicates the pore distribution of the partition walls of the ceramic honeycomb structure of Example 1 described in the best mode for carrying out the present invention. In the preferred ceramic honeycomb structure of the present invention, the cumulative pore volume with respect to each pore diameter can be made to exist between the points Δ (12) and □ (14) and the points ▲ (11) and (1) (13). It ’s fine.

In the ceramic honeycomb structure of the present invention, more preferable pore distribution of the partition walls is as follows: pore volume of pore diameter of 20 μm or more: 0.35 to 0.65 cm ³ / g, pore volume of 40 μm or more: 0.1 0.25 cm ³ / g, pore volume of 100 μm diameter or more: 0.05 cm ³ / g or less. Thus, by adjusting the pore volume between pore diameters of 20 to 100 μm to a more optimal narrow range, the communication ratio of pores of various sizes is further improved, low pressure loss, high collection efficiency, In addition, a high-strength ceramic honeycomb structure can be obtained with certainty.

  In the ceramic honeycomb structure of the present invention, the surface roughness (maximum height Ry) of the partition walls is preferably 30 μm or more. This is because if the surface roughness (maximum height Ry) of the partition walls is 30 μm or more, the fine particles can be collected more efficiently by the uneven portions formed on the surface of the porous partition walls. A more preferable range of the surface roughness (maximum height Ry) is 50 to 100 μm. In addition, there is an effect that it is easy to form a high specific surface area material that is supported together with the catalyst substance by using the uneven portions formed on the surface of the porous partition wall.

In the ceramic honeycomb structure of the present invention, by setting the thermal expansion coefficient in the flow path direction at 40 ° C. to 800 ° C. of the porous partition wall to 1.25 × 10 ⁻⁶ / ° C. or less, the thermal shock characteristics at high temperature can be obtained. It is preferable because it is improved.

  The ceramic honeycomb structure of the present invention has cordierite as the main crystal, but if the C-axis of the cordierite crystal is oriented so that it is aligned within the partition wall surface, the thermal expansion coefficient is further reduced and the thermal shock resistance is reduced. It is preferable because of its excellent resistance. In addition, other crystal phases such as mullite, zircon, aluminum titanate, silicon carbide, zirconia, spinel, Indialite, sapphirine, corundum, and titania may be contained.

  An example of a manufacturing method for obtaining the ceramic honeycomb structure of the present invention is shown below. A cordierite forming raw material such as kaolin, talc, silica, aluminum oxide, aluminum hydroxide is used as a main raw material, the cordierite forming raw material contains 5 to 35% by mass of aluminum oxide, and the aluminum oxide has a particle size of 45 μm. The above powder is contained in an amount of 5% by mass or less, a powder having a particle size of 20 μm or more at 15 to 50% by mass, a powder having a particle size of 10 μm or more is 40 to 90% by mass, and a powder having a particle size of 5 μm or more is 65 to 95% by mass. In addition, it contains 95% by mass or more of powder having a particle size of 2 μm or more, and additives such as a pore-forming agent and a binder are added to this cordierite forming raw material and kneaded. A ceramic honeycomb structure is obtained.

  As described above, when aluminum oxide has a relatively large particle diameter and contains 5 to 35% by mass of this aluminum oxide, the cordierite-forming raw material fillability (molding) in the honeycomb structure formed body. (Body density) decreases, and various fine and coarse voids exist between the cordierite forming raw materials. And this aluminum oxide is in the presence of a liquid phase produced by a cordierite forming raw material powder other than aluminum oxide such as talc and silica in a solid phase / liquid phase sintering reaction in a firing process in which cordierite is synthesized. Stablely present at relatively high temperatures where cordierite precipitates, forming partition wall constituent parts, and fine or coarse voids between cordierite forming raw materials in the ceramic molded body of the honeycomb structure remain even after firing Then, pores are formed in the ceramic fired body, and the area ratio of the partition wall constituting portion in the fracture surface of the partition wall can be set to 3 to 16%, and the maximum dimension of the partition wall constituting portion can be set to 5 to 30 μm.

  Here, the aluminum oxide exceeds 5% by mass of powder having a particle size of 45 μm or more, exceeds 50% by mass of powder having a particle size of 20 μm or more, exceeds 90% by mass of powder having a particle size of 10 μm or more, and powder having a particle size of 5 μm or more. When the content of C is over 95% by mass, the particle size of aluminum oxide is increased and the gap formed between the cordierite raw materials is increased, so that the partition wall in the fracture surface of the partition wall of the obtained ceramic honeycomb structure is obtained. The average value of the maximum dimensions of the constituent parts is less than 5 μm, and the collection efficiency and strength are reduced.

  On the other hand, the aluminum oxide does not contain powder having a particle size of 45 μm or more, powder having a particle size of 20 μm or more is less than 15% by mass, powder having a particle size of 10 μm or more is less than 40% by mass, and powder having a particle size of 5 μm or more. When the powder containing less than 65% by mass and having a particle size of 2 μm or less is less than 95%, the particle size of the aluminum oxide becomes small, and the voids formed between the cordierite forming raw materials become small. In the honeycomb structure, the average value of the maximum dimension of the partition wall constituting part of the partition wall fracture surface exceeds 30 μm, and the low pressure loss characteristic cannot be obtained.

  In order to obtain aluminum oxide having a particle size distribution as described above, it can be obtained by pulverization by a known pulverization method using a ball mill or the like, or by mixing a plurality of aluminum oxides having different particle size distributions.

  In addition, when aluminum oxide has a relatively large particle size as described above, if aluminum oxide has a rounded, substantially spherical shape, the fluidity of the raw material during extrusion molding It is preferable because it is improved.

  The reason why aluminum oxide is contained in the cordierite forming raw material is 5 to 35% by mass or less is that when the content of aluminum oxide exceeds 35% by mass, the cordierite composition cannot be maintained. Is less than 5% by mass, the amount of voids formed between the cordierite forming raw materials is reduced, so that the area ratio of the partition wall constituting part in the fracture surface of the partition wall exceeds 16%, and low pressure loss characteristics are obtained. Because it is not possible.

Here, the more preferable range of the content of aluminum oxide is 12 to 25% by mass.
This is because when the content of aluminum oxide in the cordierite forming raw material is 12% by mass or more, a preferable area ratio of 3 to 8% of the partition wall constituting portion in the partition wall fracture surface is obtained. When the content of is 25% by mass or less, since the main crystal of the ceramic honeycomb structure is maintained as cordierite, the amount of the kaolin raw material powder that is an alumina source component other than aluminum oxide can be increased. This is because it contributes to the reduction of thermal expansion due to the cordierite crystal orientation accompanying the orientation when the kaolin raw material powder passes, and the thermal shock resistance is increased. Moreover, as an alumina source component other than aluminum oxide in the cordierite forming raw material used in the present invention, those containing kaolin and / or aluminum hydroxide are preferable.

  The aluminum oxide contains 15 to 40% by mass of powder having a particle size of 20 μm or more, 50 to 70% by mass of powder having a particle size of 10 μm or more, and 70 to 85% by mass of powder having a particle size of 5 μm or more. Since the maximum dimension of the partition wall constituting portion can be 10 to 20 μm, it is more preferable.

  Among the cordierite forming raw materials, as the silica source component, quartz, fused silica, mullite, etc. can be used in addition to kaolin and talc. Among them, at least one of quartz and fused silica is used in that the coefficient of thermal expansion is lowered. It is preferable to contain 10-20 mass%, and the average particle diameter has preferable 10-30 micrometers.

  As the magnesia source component in the cordierite forming raw material, for example, talc, magnesite, magnesium hydroxide, etc. can be used, but 40 to 43% by mass of talc is contained in terms of reducing the thermal expansion coefficient. The average particle size is preferably 5 to 20 μm.

In addition, the total pore volume of the partition walls is 0.60 to 1.00 cm ³ / g, and the pore distribution of the partition walls is a pore volume having a pore diameter of 2 μm or more: 0.60 to 0.95 cm ³ / g, 5 μm or more. Pore volume: 0.60 to 0.95 cm ³ / g, 10 μm or more pore volume: 0.50 to 0.90 cm ³ / g, 20 μm or more pore volume: 0.35 to 0.70 cm ³ / g From the viewpoint of setting the pore volume of 40 μm or more: 0.10 to 0.35 cm ³ / g, and the pore volume of 100 μm or more: 0.07 cm ³ / g or less to the cordierite forming raw material, It is preferable to contain a pore-forming agent for forming the film.

  As the pore-forming agent, known flour, graphite, starch powder, ceramic balloon, polyethylene, polystyrene, polypropylene, nylon, polyester, acrylic, phenol, epoxy, ethylene-vinyl acetate copolymer, styrene-butadiene block polymer, styrene -Isoprene block polymer, polymethylmethacrylate, methylmethacrylate / acrylonitrile copolymer, urethane, wax, etc. can be used alone or in combination of one or more, but in particular methylmethacrylate / acrylonitrile copolymer A foamed resin formed by coalescence is preferred.

  Since the foamed resin formed of methyl methacrylate and acrylonitrile copolymer contains gas (isobutane) inside, a ceramic honeycomb filter having a large total pore volume can be obtained with a small amount of addition. In addition, since the calorific value of the pore forming agent in the firing step can be kept small, the problem of cracking of the ceramic honeycomb structure due to combustion of the pore forming agent, which becomes a problem during firing, can be reduced.

  However, if the amount of pore-forming agent added is large, the total pore volume of the ceramic honeycomb filter can be increased, and the strength of the ceramic honeycomb filter is reduced, which is easily damaged by mechanical shock and thermal shock during actual use. Therefore, there is an upper limit of the amount added to all pore formers, and in the case of a foamed resin formed of a methyl methacrylate / acrylonitrile copolymer, 4 to 20 parts by mass with respect to 100 parts by mass of the cordierite forming raw material It is preferable to contain, More preferably, it is 8-15 mass parts.

  Moreover, additives other than the said pore making agent can be contained as needed. For example, a binder, a dispersant, a lubricant and the like can be added. Examples of the binder include methyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, and polyvinyl alcohol. Examples of the dispersant include ethylene glycol and fatty acid soap. Examples of the lubricant include Water-soluble wax, stearic acid, etc. can be mentioned. In addition, said additive can be used individually by 1 type or in combination of 2 or more types according to the objective.

  According to the ceramic honeycomb structure of the present invention, the area ratio of the partition wall constituent portion in the fracture surface of the partition wall is 3 to 16%, and the average value of the maximum dimension of the partition wall constituent portion is 5 to 30 μm. Since the shape of the portion is optimized, it is possible to satisfy low pressure loss, high collection efficiency, and sufficient strength to withstand mechanical vibration, shock or thermal shock during use.

The ceramic honeycomb structure of the present invention can be manufactured, for example, as follows.

  After 100 parts by mass of the above cordierite forming raw material, 4 to 40 parts by mass of the pore former and 4 to 12 parts by mass of the binder and dry-mixed, 10 to 40 parts by mass of water and kneaded, Use a clay with plasticity. After this kneaded material is extruded by a known extrusion molding method, the molded body is dried by a known drying method such as microwave drying, dielectric drying, hot air drying or the like. Next, the dried honeycomb structure formed body is placed in a firing furnace and fired at a temperature of 1350 to 1440 ° C. to obtain a ceramic honeycomb structure.

  Next, after arranging the end face masking film of the ceramic honeycomb structure, the perforated portions are alternately formed in the flow path of the honeycomb structure, and the ceramic honeycomb structure is prepared in the ceramic slurry for plugging prepared in advance. The ceramic slurry is introduced into the ceramic honeycomb structure through the perforated portion of the masking film. After the introduced slurry is solidified, the honeycomb structure is extracted from the ceramic slurry and dried to form a plugging material. Further, the other end side of the honeycomb structure is introduced in the same manner, ceramic slurry is introduced, solidified, and dried to form a plugging material, and then the masking film is peeled off. Thereafter, the plugging material is fired to integrate the partition walls and the plugging material, thereby obtaining a ceramic honeycomb filter in which predetermined flow paths on the exhaust gas inflow side and the outflow side are plugged.

  The introduction of the ceramic slurry into the predetermined flow path may be performed on the dried ceramic honeycomb structure formed body, and the plugging material may be fired and integrated simultaneously with the formed body.

Hereinafter, although the actual Example of this invention is described, this invention is not limited to them.
(Examples 1-7)
The average particle size and the content of CaO + Na ₂ O + K ₂ O are the values shown in Table 1, respectively, and aluminum hydroxide, kaolin, talc, fused silica, and the average particle size, particle size distribution, and the content of CaO + Na ₂ O + K ₂ O are each Aluminum oxide B having the values shown in Table 2 was weighed at the ratio shown in Table 3. Next, as shown in Table 3, with respect to 100 parts by mass of this cordierite-forming raw material, as a pore-forming agent, isobutane-encapsulated acrylonitrile / methyl methacrylate copolymer, which is a foamed resin, and as a binder, 5 parts by mass of methylcellulose, hydroxypropyl 2 parts by mass of methylcellulose was added and mixed. Here, the particle size distributions shown in Tables 1 and 2 were measured using a laser diffraction particle size distribution analyzer LMS-30 manufactured by Seishin Enterprise Co., Ltd. Thereafter, water was added, and mixing and kneading were performed to prepare a kneaded clay, and this kneaded clay was put into an extruder to obtain a formed body having a honeycomb structure. Next, the obtained molded body was dried with a microwave dryer and then dried with hot air, and both end surfaces were cut into predetermined dimensions. Next, the end of the channel of the dried honeycomb structured body is filled with the slurry made of cordierite-forming raw material to a depth of about 10 mm from the end and dried, and both ends of the channel of the structure shown in FIG. A dried ceramic honeycomb body in which the plugs were alternately plugged was obtained. Thereafter, firing was performed at 1420 ° C. for 10 hours, and the ceramic honeycomb structures of Examples 1 to 7 having dimensional characteristics of Φ143.8 mm, length 152.4 mm, partition wall thickness 300 μm, partition wall pitch 1.58 mm were obtained. Obtained.

(Comparative Example 1)
A ceramic honeycomb structure of Comparative Example 1 was obtained in the same manner as in Examples 1 to 7, except that the content of aluminum oxide B was 4.5%.

(Examples 8 to 13)
In contrast to Example 4, aluminum oxide A was used in place of aluminum oxide B, and as a pore-forming agent, isobutane encapsulated acrylonitrile-methyl methacrylate copolymer, graphite, polymethyl methacrylate (PMMA), polyethylene, wheat flour as a foaming resin The ceramic honeycomb structures of Examples 8 to 13 were obtained in the same manner except that was used as shown in Table 3.

(Examples 14 to 18)
The ceramic honeycomb structures of Examples 14 to 18 were obtained in the same manner as in Example 4 except that aluminum oxides F, G, H, I, and J were used instead of aluminum oxide B.

(Comparative Examples 2 to 4)
The ceramic honeycomb structures of Comparative Examples 2 to 4 were obtained in the same manner as in Example 4 except that aluminum oxides C, D, and E were used instead of aluminum oxide B.

Table 4 shows the results of evaluating the pressure loss characteristics, the collection rate of fine particles, and the filter characteristics of isostatic strength for the obtained Examples 1 to 18 and Comparative Examples 1 to 4 ceramic honeycomb structures.

The pressure loss characteristic was measured by the following method. After the ceramic honeycomb structure is installed in a pressure loss test stand, the air pressure of 7.5 Nm ³ / min is flowed and the pressure difference between the inflow side and the outflow side of the ceramic honeycomb structure is measured to determine the initial pressure loss. Then, carbon powder with an average particle size of 0.042 μm was charged at a supply rate of 3 g / h, and after a certain time had elapsed, the pressure loss was obtained by measuring again the differential pressure when 1 g of carbon was collected per liter of the ceramic honeycomb structure. It was. Then, the pressure loss at a carbon powder collection amount of 1 g / L is calculated as the pressure loss increase rate with respect to the initial pressure loss, the pressure loss increase rate at the time of carbon collection being 15% or less is excellent, and 15% or more and less than 20% is good. 20% or more was evaluated and judged as “bad”.

  The collection rate was determined as the ratio of the weight increase of the ceramic honeycomb structure after collecting the carbon powder to the input amount of the carbon powder. The evaluation of the collection efficiency was evaluated with a collection efficiency of 95% or more as excellent, ◎, 90% or more and less than 95% as good ○, and less than 90% as unsatisfactory.

  Thereafter, the ceramic honeycomb structure after the test was heated at 600 ° C. for 5 hours to burn and remove carbon, and an isostatic test of the ceramic honeycomb structure after carbon removal was performed. In the isostatic test, the water pressure when broken by hydrostatic pressure was measured using an isostatic test device to obtain isostatic strength. The evaluation of the isostatic strength was evaluated with an isostatic strength of 1.5 MPa or more as excellent 優, 1.0 MPa or more and less than 1.5 MPa as good ○, and less than 1.0 MPa as unsatisfactory ×.

Thereafter, a test piece was cut out from the broken ceramic honeycomb structure after completion of the isostatic test, and the area ratio and the maximum dimension of the partition wall constituting portion, the total pore volume of the partition wall, and the pore distribution in the partition wall fracture surface were obtained. Measurement of the area ratio and the average value of the maximum dimensions of the partition wall constituent portions in the partition wall fracture surface was performed as follows. First, the fracture surface of an arbitrary partition wall is observed with an SEM, a field of view of 0.8 × 0.8 mm is selected, a photograph is taken, the inside of the photographed field of view is further increased (250 to 1000 times), and is brittle. Considering the part that was the fracture surface as the partition wall component, blacken it on the photo and binarize it, and then analyze the image of this black coating to obtain the average value of the area ratio and maximum dimension of the partition wall component. Asked. The measurement was performed at 10 locations on the fracture surface of the partition walls of the ceramic honeycomb structure of each example, and an average value was obtained. On the other hand, the measurement of the total pore volume and pore distribution of the partition walls is performed by using a mercury intrusion method, using Autopore III manufactured by Micromeritics, and a small piece cut out from the ceramic honeycomb filter is stored as a test piece in a measurement cell, After depressurizing the inside of the cell, mercury was introduced and pressurized, and the relationship between the pore diameter and the cumulative pore volume was determined from the relationship between the pressure at this time and the volume of mercury pushed into the pores existing in the sample. Ask for. At this time, the pressure for introducing mercury was 0.5 psi (0.35 × 10 ⁻³ kg / mm ² ), and the constants for calculating the pore diameter from the pressure were contact angle = 130 °, surface tension 484 dyne / cm. It was.

  Furthermore, the surface roughness (maximum height Ry) of the partition wall surface was measured according to (JIS) B 0601-1994.

The ceramic honeycomb structures of Examples 1 to 7 contain 7.0 to 34.9% by mass of aluminum oxide B among the cordierite forming raw materials, and the aluminum oxide B contains 5 powders having a particle diameter of 45 μm or more. 15% to 50% by mass of powder having a particle size of 20 μm or less, 40 to 90% by mass of powder having a particle size of 10 μm or more, 65 to 95% by mass of powder having a particle size of 5 μm or more, and 2 μm or more of particle size Therefore, the partition wall portion of the partition wall fracture surface has an area ratio of 3.0 to 15.9%, and the average maximum dimension of the partition wall portion is 5.2. It was -9.7 micrometers. Moreover, since it contains 12 parts by mass of foamed resin as a pore-forming agent, pores of various sizes are arranged in a well-balanced manner, and the total pore volume of the partition walls is 0.60 to 1.00 cm ³ / g. The pore distribution was such that the pore volume with a pore diameter of 2 μm or more: 0.60 to 0.95 cm ³ / g, the pore volume with 5 μm or more: 0.60 to 0.95 cm ³ / g, 10 μm or more. pore volume: 0.50~0.90cm ³ / g, 20μm or more of the pore volume: 0.35~0.70cm ³ / g, 40μm or more of the pore volume: 0.10~0.35cm ³ / g The volume of pores with a diameter of 100 μm or more was 0.07 cm ³ / g or less. For this reason, the ceramic honeycomb structures of Examples 1 to 7 all passed (◯) or (◎) that passed the evaluation results of the pressure loss, the collection rate, and the isostatic strength.

  Among them, the ceramic honeycomb structures of Examples 3 to 7 contain 12% by mass or more of aluminum oxide B in the cordierite forming raw material. It was ˜7.9%, and the pressure loss was excellent (◎).

  On the other hand, among the cordierite forming raw materials, the ceramic honeycomb structure of Comparative Example 1 in which the content of aluminum oxide B was 4.5% had an area ratio of partition wall constituent portions in the partition wall cross section of 17.4%. The pressure loss was not possible (x).

Moreover, the ceramic honeycomb structures of Examples 8 to 13 contain 22.0% by mass of aluminum oxide A among the cordierite forming raw materials, and 5% by mass of the aluminum oxide A having a particle diameter of 45 μm or more. Hereinafter, powder having a particle size of 20 μm or more is contained at 15 to 40% by mass, powder having a particle size of 10 μm or more is 50 to 70% by mass, powder having a particle size of 5 μm or more is 70 to 85% by mass, and powder having a particle size of 2 μm or more. The partition wall constituent part in the partition wall fracture surface has an area ratio of 4.5 to 7.9%, and the average value of the maximum dimension of the partition wall constituent part is It was 14.9 to 19.6 μm. For this reason, in the ceramic honeycomb structures of Examples 8 to 13, the evaluation results of the pressure loss, the collection rate, and the isostatic strength were all acceptable (◯) or (）). Among them, since the ceramic honeycomb structures of Examples 8, 10, 12, and 13 contained 4 to 12 parts by mass of the foamed resin in the pore forming agent, the total pore volume of the partition walls was 0.60 to 1. a .00cm ³ / g, pore distribution, pore size 2μm or more pore volume: 0.60~0.95cm ³ / g, 5μm or more pore volume: 0.60~0.95cm ³ / g, 10μm or more of the pore volume: 0.50~0.90cm ³ / g, 20μm or more of the pore volume: 0.35~0.70cm ³ / g, 40μm or more of the pore volume: 0.10 to 0 .35 cm ³ / g, pore volume of 100 μm diameter or more: 0.07 cm ³ / g or less, and the evaluation results of pressure loss, collection rate, and isostatic strength were all excellent (◎).

The ceramic honeycomb structures of Examples 14 and 15 contained 22.0% by mass of aluminum oxides H and I among the cordierite forming raw materials, and the aluminum oxides H and I had a particle size of 45 μm. The above powder is contained at 0.3 to 0.5% by mass, the powder having a particle size of 20 μm or more is contained at 15.6 to 16.5% by mass, and the powder having a particle size of 10 μm or more is contained at 43.6 to 46.5% by mass. The partition wall fracture surface has a particle size distribution containing 66.5 to 69.8% by mass of powder having a particle size of 5 μm or more and 96.0 to 96.5% by mass of powder having a particle size of 2 μm or more. The area ratio of the partition wall constituting portion was 6.5 to 7.7%, and the average value of the maximum dimension of the partition wall constituting portion was 24.5 to 29.7 μm. Moreover, since it contains 12 parts by mass of foamed resin as a pore-forming agent, pores of various sizes are arranged in a well-balanced manner, and the total pore volume of the partition walls is 0.60 to 1.00 cm ³ / g. The pore distribution was such that the pore volume with a pore diameter of 2 μm or more: 0.60 to 0.95 cm ³ / g, the pore volume with 5 μm or more: 0.60 to 0.95 cm ³ / g, 10 μm or more. pore volume: 0.50~0.90cm ³ / g, 20μm or more of the pore volume: 0.35~0.70cm ³ / g, 40μm or more of the pore volume: 0.10~0.35cm ³ / g The volume of pores with a diameter of 100 μm or more was 0.07 cm ³ / g or less. For this reason, in the ceramic honeycomb structures of Examples 14 and 15, the evaluation results of the pressure loss, the collection rate, and the isostatic strength were all acceptable (◯) or (◎).

Moreover, the ceramic honeycomb structures of Examples 16 and 17 were made of 22.0 of aluminum oxide F and G in which aluminum oxide was appropriately mixed with aluminum oxide B and C having two kinds of particle sizes among the cordierite forming raw materials. Powders containing 5% by mass of powders having a particle size of 45 μm or more and 15-40% by mass of powders having a particle size of 20 μm or more, and containing aluminum oxides F and G having a particle size of 45 μm or more. 50 to 70% by mass, powder having a particle size of 5 μm or more has a preferred particle size distribution of 70 to 85% by mass, and powder having a particle size of 2 μm or more has a preferable particle size distribution of 95% by mass or more. The area ratio of the portion was 6.6 to 7.3%, and the average value of the maximum dimension of the partition wall constituting portion was 15.6 to 16.5 μm. Moreover, since it contains 12 parts by mass of foamed resin as a pore-forming agent, pores of various sizes are arranged in a well-balanced manner, and the total pore volume of the partition walls is 0.60 to 1.00 cm ³ / g. The pore distribution was such that the pore volume with a pore diameter of 2 μm or more: 0.60 to 0.95 cm ³ / g, the pore volume with 5 μm or more: 0.60 to 0.95 cm ³ / g, 10 μm or more. pore volume: 0.50~0.90cm ³ / g, 20μm or more of the pore volume: 0.35~0.70cm ³ / g, 40μm or more of the pore volume: 0.10~0.35cm ³ / g The volume of pores with a diameter of 100 μm or more was 0.07 cm ³ / g or less. For this reason, the ceramic honeycomb structures of Examples 16 and 17 all had excellent (が) evaluation results of pressure loss, collection rate, and isostatic strength.

The ceramic honeycomb structure of Example 18 contained 22.0% by mass of aluminum oxide J among the cordierite forming raw materials, and the aluminum oxide J was 1.4% by mass with a particle size of 45 μm or more. %, A powder having a particle size of 20 μm or more at 45.6% by mass, a powder having a particle size of 10 μm or more is 85.7% by mass, a powder having a particle size of 5 μm or more is 94.2% by mass, and a powder having a particle size of 2 μm or more. Therefore, the partition wall portion of the partition wall fracture surface has an area ratio of 6.8%, and the average maximum dimension of the partition wall portion is 5.2 μm. Met. Moreover, since it contains 12 parts by mass of foamed resin as a pore-forming agent, pores of various sizes are arranged in a well-balanced manner, and the total pore volume of the partition walls is 0.60 to 1.00 cm ³ / g. The pore distribution was such that the pore volume with a pore diameter of 2 μm or more: 0.60 to 0.95 cm ³ / g, the pore volume with 5 μm or more: 0.60 to 0.95 cm ³ / g, 10 μm or more. pore volume: 0.50~0.90cm ³ / g, 20μm or more of the pore volume: 0.35~0.70cm ³ / g, 40μm or more of the pore volume: 0.10~0.35cm ³ / g The volume of pores with a diameter of 100 μm or more was 0.07 cm ³ / g or less. For this reason, the ceramic honeycomb structure of Example 18 was evaluated as (◯) or (◎) that passed the evaluation results of pressure loss, collection rate, and isostatic strength.

  On the other hand, among the cordierite forming raw materials, aluminum oxide contains less than 15% by weight of powder having a particle size of 20 μm or more, less than 40% by weight of powder having a particle size of 10 μm or more, and less than 65% by weight of powder having a particle size of 5 μm or more. In the ceramic honeycomb structures of Comparative Examples 2 and 3 using the aluminum oxides C and F, the average value of the maximum dimension of the partition wall constituting part in the partition wall fracture surface exceeded 30 μm, so the determination of the pressure loss was unsuccessful. (X).

  Among the cordierite forming materials, aluminum oxide contains powder with a particle size of 20 μm or more exceeding 50 mass%, powder with a particle size of 10 μm or more exceeding 90 mass%, and powder with a particle size of 5 μm or more exceeding 95 mass% In the ceramic honeycomb structure of Comparative Example 4 using aluminum oxide D, the average value of the maximum dimension of the partition wall constituting part in the partition wall fracture surface was less than 5 μm, so that the determination of the collection rate and isostatic strength was not possible. It was a pass (x).

(1) And (2) is the front view and side view which respectively show an example of a ceramic honeycomb filter. It is a figure which shows an example binarized into the partition component part and non-partition component part of the partition fracture surface of the ceramic honeycomb structure of this invention. It is a figure which shows the relationship between the pore diameter of the ceramic honeycomb structure of this invention, and a cumulative pore volume. The schematic diagram which shows the form of the partition cross section of a ceramic honeycomb structure.

Explanation of symbols

1: partition wall,
2: flow path,
3: Ceramic honeycomb filter,
4: plugging material 5: fracture surface 11: point indicating the lower limit of the preferred total pore volume of the ceramic honeycomb structure of the present invention 12: point indicating the upper limit of the preferred total pore volume of the ceramic honeycomb structure of the present invention 13: A point indicating a lower limit of a preferable cumulative pore volume at a pore diameter of 2 μm or more, 5 μm or more, 10 μm or more, 20 μm or more, 40 μm or more of the ceramic honeycomb structure of the present invention 14: Pore diameter of the ceramic honeycomb structure of the present invention 2 μm As described above, the upper limit of the preferred cumulative pore volume at 5 μm or more, 10 μm or more, 20 μm or more, or 40 μm or more 15: Pore distribution of the ceramic honeycomb structure of Example 1 of the present invention A: A cut surface is schematically shown in the partition wall section Line B: Line that schematically represents the fracture surface in the partition wall section

Claims (2)

  It is contained in the exhaust gas by plugging a predetermined flow path of the ceramic honeycomb structure made of a material having cordierite as a main crystal and allowing the exhaust gas to pass through a porous partition wall that defines the flow path. A ceramic honeycomb structure used for a ceramic honeycomb filter for removing fine particles, wherein an area ratio of partition wall constituent parts in the fracture surface of the partition walls is 3 to 16%, and an average value of maximum dimensions of the partition wall constituent parts is A ceramic honeycomb structure having a thickness of 5 to 30 μm. The total pore volume of the partition wall is 0.60 to 1.00 cm ³ / g, and the pore distribution of the partition wall is a pore volume having a pore diameter of 2 μm or more: 0.60 to 0.95 cm ³ / g, 5 μm The above pore volume: 0.60 to 0.95 cm ³ / g, the pore volume of 10 μm or more: 0.50 to 0.90 cm ³ / g, the pore volume of 20 μm or more: 0.35 to 0.70 cm ³ 2. The ceramic honeycomb structure according to claim 1, wherein the pore volume is 40 μm or more: 0.10 to 0.35 cm ³ / g and the pore volume is 100 μm or more: 0.07 cm ³ / g or less. body.

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