JP2004181458A - Hexagonal cell honeycomb structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hexagonal cell honeycomb structure, which is particularly preferably used as a catalyst carrier for purifying car exhaust gas, has high mechanical strength and good purification capability, and causes small pressure loss. <P>SOLUTION: A hexagonal cell honeycomb structure 1 has multiple cell passage partitions 2, wherein the cross section of a cell 3 is hexagon-shaped. In this case, the partition angle (θ) is 30°, and the ratio (C/B) of the average compression breakdown strength of a C-axis to that of a B-axis of the hexagonal cell honeycomb structure 1 is set at 0.9 or more. Alternatively, the range of the partition angle (θ) is determined to be 30°<θ<45°, and the isostatic breakdown strength is determined to be 4 MPa or more. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention relates to a honeycomb structure preferably used as a catalyst carrier for automobile exhaust gas purification and a gripping method thereof, and more particularly, to a hexagonal cell honeycomb structure having high mechanical strength, good purification performance, and low pressure loss. The present invention relates to a body and a gripping method thereof.

  In recent years, due to the rise of the global environmental protection movement, stricter exhaust gas regulations are being promoted in each country. Along with this, improvements have been made to reduce the emission of harmful substances such as hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx) from the engine itself, and are now mainstream. Improvements in three-way purification catalysts for exhaust gas have also progressed, and both of these effects tend to steadily reduce emissions of harmful substances.

  Thus, while the overall emissions during normal driving conditions are reduced, the amount of harmful substances emitted immediately after starting the engine is highlighted. For example, in the case of FTP-75, which is a regulated driving cycle in the United States, 60 to 80% of the total amount discharged in the entire driving cycle in 140 seconds immediately after the engine is started is regarded as a problem.

  This is because the exhaust gas temperature is low immediately after the start of the engine, so that the catalyst is not sufficiently activated, and harmful substances pass through the catalyst without being purified. Immediately after the start of the engine, the combustion state is not stable, and the A / F (air-fuel ratio) of the exhaust gas, which is an important factor affecting the purification performance of the three-way catalyst, that is, the ratio of the oxygen amount in the exhaust gas, The fluctuation is one of the causes.

  Here, when the A / F reaches the stoichiometric air-fuel ratio of 14.7, the catalyst exhibits the most effective purification performance. For this reason, in order to raise the temperature of the catalyst immediately after the engine is started, the position of the catalyst is placed as close to the engine as possible and the catalyst is placed in a place where the exhaust gas temperature is high, or the heat capacity of the honeycomb structure itself as the catalyst carrier is reduced. Alternatively, in order to absorb the heat of the exhaust gas quickly and increase the contact area between the catalyst and the exhaust gas, a device for increasing the cell density of the honeycomb structure has been devised.

  In the engine, improvements have been made to make the A / F reach the stoichiometric air-fuel ratio as soon as possible. On the other hand, in the case of a catalyst, ceria and zirconia are added to a noble metal such as platinum, rhodium and palladium having a catalytic action to store and desorb oxygen in an exhaust gas in order to suppress the fluctuation of A / F as much as possible. Means are being taken. These noble metals and oxygen storage substances are present dispersed in the pores of the γ-alumina layer carried on the surface of the porous cell passage partition walls (ribs) in the honeycomb structure.

As a specific example of the above-mentioned improvement, the cross-sectional shapes of the cells are triangular (triangular cells), quadrangular (quadrangular cells), and hexagonal (hexagonal cells). (For example, see Patent Document 1). Further, a honeycomb structure in which a hexagonal cell is provided with a curve or R (radius of 1 mm or more) at a cell corner is disclosed (for example, see Patent Document 2). Further, a hexagonal cell is used in a honeycomb structure having a rib thickness of 0.05 to 0.150 mm, an opening ratio of 0.65 to 0.95 and upper and lower limits of bulk density (for example, see Patent Document 3). A honeycomb structure (having a rib wall thickness of 0.17 mm and a cell density of 62 cells / cm ² ) composed of hexagonal cells arranged near an engine is disclosed (for example, see Patent Document 4).
JP-A-56-147637 JP-A-62-225250 JP-A-7-39760 JP-A-8-193512

  However, in the honeycomb structure composed of hexagonal cells described in Patent Document 1 (Japanese Patent Application Laid-Open No. 56-147637) (hereinafter, referred to as “hexagonal cell honeycomb structure”), a coating such as γ-alumina accumulates at the cell corners. It is another object of the present invention to avoid the above problem and to make the exhaust gas efficiently contact the noble metal supported on the γ-alumina layer. In addition, the hexagonal cell honeycomb structure described in Patent Document 2 (Japanese Patent Application Laid-Open No. 62-225250) is made for the purpose of avoiding the film accumulated at the cell corners from peeling off due to impact or thermal change. In the examples, there is no description about the rib thickness and the cell density of the hexagonal cell honeycomb structure.

  On the other hand, the invention described in Patent Document 3 (Japanese Patent Application Laid-Open No. 7-39760) aims to increase the opening temperature and reduce the heat capacity of the carrier while reducing the pressure loss, thereby increasing the catalyst temperature rise at the time of cold start. . Further, Patent Document 4 (Japanese Patent Application Laid-Open No. 8-193512) discloses that a hexagonal cell honeycomb structure having better thermal shock resistance than a triangular cell honeycomb structure or a square cell honeycomb structure is placed near an engine having a high exhaust gas temperature. It is stated that the arrangement improves the warm-up characteristics of the catalyst. However, on the other hand, since the triangular cell honeycomb structure and the square cell honeycomb structure have a larger GSA (Geometric Surface Area) at the same cell density than the hexagonal cell honeycomb structure, the warm-up is completed. After that, since a triangular cell or a square cell has better purification performance than a hexagonal cell, it is described that a triangular cell honeycomb structure or a square cell honeycomb structure is preferable for a catalyst located farther from the engine.

  As described above, the above prior art is mainly made from the viewpoint of durability in the purification performance and the catalytic performance, and does not consider the strength of the honeycomb structure. In the conventional honeycomb structure, there are mainly three types: a triangular cell, a square cell, and a hexagonal cell. Among them, a square cell, particularly a square cell, is most often employed. This is largely due to the fact that the square cell has a better balance in terms of purification performance, pressure loss performance, and strength than other shapes, and is easy to make a die used when extruding a honeycomb structure. Therefore, when these are compared under the condition of the same rib thickness and the same cell density, the prior art is ranked as shown in Table 1.

  The hexagonal cell honeycomb structure is substantially equivalent to the square cell honeycomb structure in purification performance, and is excellent in pressure loss performance, but is structurally low in rigidity and low in strength. It has not been put to practical use until now. Therefore, the hexagonal cell honeycomb structure has been limited to practical use in a stationary device that does not require a very large strength, such as an application for a catalyst carrier for deodorization.

The present invention has been made in view of the above-described problems of the related art, and an object of the present invention is to improve the strength characteristics of a hexagonal cell honeycomb structure, and to convert a hexagonal cell honeycomb structure into an automotive exhaust gas purification. The purpose is to make it practical as a catalyst carrier.
That is, according to the present invention, there is provided a honeycomb structure having a plurality of cell passage partition walls, wherein the cross-sectional shape of the cell is hexagonal, and in the cross section, a pair of opposed vertexes of the hexagonal cell are connected, and the hexagonal cell is formed. Is the axis that is symmetrical with respect to the axis, the axis perpendicular to the C axis in the cross section is the B axis, and the angle between one side of the hexagonal cell that intersects the C axis and the B axis is the partition wall angle (θ Then, the partition wall angle (θ) is 30 °, and the ratio (C / B) of the average of the C-axis compressive breaking strength and the average of the B-axis compressive breaking strength of the honeycomb structure is 0.9 or more. A hexagonal cell honeycomb structure is provided. In this hexagonal cell honeycomb structure, the isostatic breaking strength is preferably 4 MPa or more.

  According to the present invention, there is provided a honeycomb structure having a plurality of cell passage partition walls, wherein a cross-sectional shape of the cell is hexagonal, and a pair of vertexes of the hexagonal cell facing each other in the cross section are connected, and a hexagonal cell is formed. Is the axis that is symmetrical with respect to the axis, the axis perpendicular to the C axis in the cross section is the B axis, and the angle between one side of the hexagonal cell that intersects the C axis and the B axis is the partition wall angle (θ ) Provides a hexagonal cell honeycomb structure characterized in that the range of the partition wall angle (θ) of the cell is 30 <θ <45 ° and the isostatic breakdown strength is 4 MPa or more. In this hexagonal cell honeycomb structure, the range of the partition wall angle θ is more preferably 35 <θ <40 °.

  The above-described hexagonal cell honeycomb structure of the present invention is preferably made of a ceramic material or a heat-resistant metal steel of cordierite, alumina, mullite, silicon nitride, silicon carbide, or zirconia. Stainless steel is preferably used. Further, the above-mentioned hexagonal cell honeycomb structure is preferably used as a catalyst carrier for purifying automobile exhaust gas.

  According to the hexagonal cell honeycomb structure of the present invention (hereinafter, referred to as “hexagonal cell honeycomb”), mechanical strength is improved, and by stably gripping the hexagonal cell honeycomb, it is particularly suitable for automobile exhaust gas purification. When used as a catalyst carrier, excellent durability performance, purification performance, and low pressure loss performance can be obtained.

Hereinafter, embodiments of the present invention will be described.
FIG. 1 is a sectional view showing an embodiment of the hexagonal cell honeycomb of the present invention. The hexagonal cell honeycomb 1 has a cell passage partition wall 2 for isolating a plurality of cells 3, and the cross-sectional shape of the cells 3 is a hexagonal shape (hexagonal cell 3). Here, the shape factors that determine the shape of the hexagonal cell 3 are a partition wall angle θ, a partition wall thickness t, a partition wall length h and L, as shown in a partially enlarged view in FIG. Here, the partition wall angle θ refers to an angle between one side of the hexagonal cell 3 intersecting the C axis and the B axis. Therefore, as shown in FIG. 1, when the cell shape is a regular hexagon, θ = 30 degrees, and the aspect ratio (h / L) of the partition length is 1. The definitions of the B axis and the C axis will be described later.

  However, in the hexagonal cell honeycomb 1 of the present invention, it is not always necessary that the cell shape is a regular hexagon, and a hexagonal shape capable of densely filling a plurality of hexagons, for example, a pair of opposing sides is formed. The length h may be slightly longer or shorter than the length L of the other side.

  In such a hexagonal cell 3, as shown in FIG. 2, since each vertex 7 has an obtuse angle, the γ-alumina catalyst layer 6 (hereinafter referred to as “coating”) formed on the cell passage partition 2 is smaller than the triangular cell 5 or the square cell 4. , "Coat layer 6") has a uniform thickness, so that the purification catalyst can effectively and entirely contact the exhaust gas, and the purification performance of the catalyst can be improved. Further, since the hydraulic diameter R can be increased, the pressure loss can be reduced.

  Furthermore, since the coat layer 6 is formed uniformly, the heat of the exhaust gas is uniformly transmitted throughout the coat layer 6 and further to the cell passage partition walls 2, so that the temperature of the hexagonal cell honeycomb 1 is more quickly and uniformly. And warm-up performance is improved. Further, since the coat layer 6 itself is also heated quickly and uniformly, the catalyst components distributed in the coat layer 6 exhibit uniform activity as a whole, and as a result, the warm-up characteristics of the catalyst are improved. And the purification performance is improved.

  In recent years, a method has been developed in which a catalyst layer has a two-layer structure or a multilayer structure in which different catalyst components are supported on each layer for the purpose of improving catalyst performance and suppressing catalyst deterioration. In the multilayer structure, it is considered that such uniformity of the thickness of each coat layer has a great influence on the catalytic activity. That is, since the layer (lower layer) near the cell passage partition 2 is farther from the exhaust gas than the layer (upper layer) facing the cell passage through which the exhaust gas passes, the temperature rise becomes slower than that of the upper layer, and it takes time until the catalytic activity appears. A big problem such as The effect of the uniformity of the thickness of the coat layer 6 in such a hexagonal cell honeycomb is not limited to the case where a three-way catalyst is used, and can be expected for various catalysts such as zeolite and metal. Therefore, also from such a point, it can be said that the hexagonal cell honeycomb has excellent characteristics.

  Next, the mechanical characteristics of the hexagonal cell honeycomb 1 will be described. Generally, the evaluation of the mechanical strength of the honeycomb structure is evaluated by the compressive fracture strength in the axial direction and the isostatic strength. Here, the compressive fracture strength is one of the mechanical properties required for a honeycomb structure as a mechanical structural member, and the A-axis is used for a square cell shape according to the automotive standard JASO standard M505-87 issued by the Automotive Engineering Society of Japan. , B axis, and C axis are to be measured.

  However, regarding the hexagonal cell honeycomb 1, how to take each axis is not specified. Therefore, in the present invention, the C axis is an axis that connects a pair of vertexes facing each other in the hexagonal cell 3 and that the hexagonal cell 3 has a shape symmetrical with respect to the C axis. The B axis is defined as an axis perpendicular to both the A axis and the C axis when the direction is perpendicular to the cross section of the cell 3 which is the direction of the passage.

  At this time, the B-axis compressive fracture strength is a cylindrical sample of 25.4 mmφ × 25.4 mm in which the end face is parallel to the A-C axis cross section and the B-axis is the length direction from the B-axis direction of the hexagonal cell honeycomb. Is cut out, and the fracture load when compressed in the B-axis direction is divided by the area of the compressed surface. Similarly, the C-axis compressive fracture strength is obtained by cutting a 25.4 mmφ x 25.4 mm cylindrical sample cut out so that the end face is parallel to the AB axis plane and the C axis is the length direction in the C axis direction. Measured with compression. The A-axis compressive fracture strength is determined by taking out the same cylindrical sample having an end surface parallel to the cell passage cross section (BC cross section) and the A-axis as the length direction from the hexagonal cell honeycomb 1, It is given by a value obtained by dividing the breaking load when compressed in the A-axis direction by the area of the compressed surface.

  On the other hand, since the isostatic breaking strength is usually mounted by adopting the structure by holding the outer peripheral surface of the catalyst carrier, the catalyst carrier for purifying automobile exhaust gas has sufficient strength and durability against the holding surface pressure. It is a useful property to evaluate whether or not. This isostatic fracture strength test is a test in which a carrier is placed in a rubber cylindrical container, covered with an aluminum plate, and subjected to isostatic pressure compression in water. In the test simulating the compressive load applied in the case of, the isostatic breaking strength is indicated by the pressure value at the time when the carrier breaks, and is defined by the automotive standard JASO standard M505-87 issued by the Japan Society of Automotive Engineers. ing.

  Regarding these various breaking strengths, as shown in the examples described later, a clear difference is shown between the ratio between the C-axis compression breaking strength and the B-axis compression breaking strength (compression breaking strength ratio C / B) and the isostatic breaking strength. A correlation is seen, and it is preferable in terms of isostatic breaking strength that the compressive breaking strength ratio C / B is 0.9 or more.

  Also, as the partition wall angle θ increases, the ratio of the average values of the compressive breaking strengths of the C axis and the B axis increases, and both the C axis compressive breaking strength and the isostatic breaking strength improve. If θ becomes too large, it tends to decrease. Therefore, the balance between the compressive breaking strengths of the C-axis and the B-axis has an important effect on the improvement of the isostatic breaking strength. By increasing the partition wall angle θ beyond the normal 30 °, the C-axis compression strength is improved. It is possible to improve both the breaking strength and the isostatic breaking strength. From the viewpoint of isostatic breaking strength, the range of the partition wall angle θ is preferably 30 ° <θ <45 °, and more preferably 35 ° <θ <40 °.

  In the present invention, the material forming the hexagonal cell honeycomb 1 is preferably made of any one of cordierite, alumina, mullite, silicon nitride, silicon carbide, and zirconia, or a heat-resistant metal steel, particularly stainless steel. The mechanical characteristics of the hexagonal cell honeycomb 1 described above are considered to be caused by the geometrical characteristics of the hexagonal cell 3. Therefore, if the material is different, the mechanical strength value itself is different. For example, the preferable partition wall angle θ, the compressive breaking strength ratio C / B, and the like can be considered as parameters for universal mechanical strength characteristics independent of the manufacturing method and the material.

  The hexagonal cell honeycomb of the present invention has low pressure loss performance and excellent mechanical properties, and when a hexagonal cell honeycomb is provided with a coating layer, excellent exhaust gas purification performance is obtained, so that automobile exhaust gas is obtained. It is particularly suitably used as a purification catalyst carrier. The hexagonal cell honeycomb of the present invention is used not only as a catalyst carrier for purifying automobile exhaust gas, but also as a catalyst carrier for various exhaust gas purification treatments, various exhaust gas particulate filtration filters, various liquid filtration filters, various chemical reaction catalyst carriers, and the like. It can be applied when the structure needs to be gripped by some external pressure.

  Next, a method of holding the hexagonal cell honeycomb will be described. When the hexagonal cell honeycomb is used as an exhaust gas purifying catalyst carrier, the catalyst carrier is gripped by a can body on the outer peripheral surface thereof, and is used as a converter. Therefore, when the hexagonal cell honeycomb is gripped on its outer peripheral surface, the mechanical properties described above, particularly when the partition wall angle θ is larger than 30 °, the C-axis compressive breaking strength is higher than the B-axis compressive breaking strength. In consideration of the above, it is preferable that the hexagonal cell honeycomb is gripped on the outer peripheral surface thereof mainly in the C-axis direction. Therefore, when the shape of the hexagonal cell honeycomb in the cross section taken along the line B-C perpendicular to the passage direction of the hexagonal cell is an ellipse or an ellipse, the C-axis direction of the hexagonal cell honeycomb is changed to the minor axis of the ellipse or the ellipse. When gripping in the C-axis direction in accordance with the direction, the gripping can be performed stably and firmly, and the reliability is excellent.

  On the other hand, when the partition wall angle θ in the cell 3 has a shape of 30 ° or less, the B-axis compressive breaking strength is larger than the C-axis compressive breaking strength, as shown in Examples described later. Therefore, in such a case, the hexagonal cell honeycomb is preferably gripped in the B-axis direction on the outer peripheral surface thereof. When the hexagonal cell honeycomb has an elliptical or elliptical cross-sectional shape along the BC axis, Gripping in the B-axis direction with the B-axis direction coinciding with the minor axis direction of these ellipses or ellipses is the most stable and strong way to grip the hexagonal cell honeycomb.

  In any case of the above-described gripping in the C-axis direction and the gripping in the B-axis direction, the shape of the hexagonal cell honeycomb in the BC axis cross section is not limited to an ellipse or an ellipse, but may be a circle, a rectangle, or a polygon. The gripping direction may be determined according to the shape of the hexagonal cells forming the honeycomb structure (partition wall angle θ).

  Hereinafter, the present invention will be described in more detail with reference to Examples.

  A kneaded raw material composed of talc, kaolin, alumina or the like was extruded, dried and fired to produce a cordierite hexagonal cell honeycomb, which was subjected to a test. Table 2 shows various parameters for specifying the shape of the manufactured hexagonal cell honeycomb. Here, for example, a cell number of 600 Cpsi means that there are 600 cells per square inch.

  The honeycomb structure as a catalyst carrier for automobile exhaust gas purification has three basic performances of compressive breaking strength, isostatic breaking strength and thermal shock resistance in addition to the catalyst carrying performance, that is, the ability to form a coating layer. It is required to be excellent. Therefore, in the test of the manufactured hexagonal cell honeycomb, for the compressive fracture strength test, the isostatic fracture strength test and the thermal shock test, 5 or 10 pieces were tested for each shape of the honeycomb structure, and the average value was obtained. went. The test results are listed in Table 2.

  Here, the compression fracture strength test is performed according to the regulations for square cells in the automotive standard JASO standard M505-87 issued by the Society of Automotive Engineers of Japan described above, A-axis, B-axis defined in the hexagonal cell honeycomb of the present invention, Performed for each axis of the C-axis. For example, the B-axis compressive fracture strength is 25.4 mmφ ×, where the end face is parallel to the AC-axis cross section and the B-axis is the length direction from the B-axis direction of the hexagonal cell honeycomb. It is given by a value obtained by dividing a 25.4 mm cylindrical sample and compressing it in the B-axis direction by the fracture load divided by the area of the compressed surface. The same applies to the other A-axis and C-axis.

  In addition, the isostatic fracture strength test was performed based on the regulations of the automotive standard JASO standard M505-87 issued by the Society of Automotive Engineers of Japan. The basic method of the thermal shock resistance test is specified in JASO standard M505-87. The honeycomb structure at room temperature is placed in an electric furnace maintained at a temperature higher than room temperature by a predetermined temperature and held for 20 minutes. Take out the carrier, observe the appearance and tap the outer periphery of the carrier with a metal rod. If no cracks were observed and the tapping sound was not a dull metal sound, the test passed and the same test was repeated every time the temperature in the electric furnace was raised in steps of 50 ° C. until the test was rejected. Therefore, if the test fails at room temperature + 950 ° C., the thermal shock resistance is 900 ° C. different.

  Next, the test results will be considered. First, the slit of the portion for forming the honeycomb of the extrusion die used in manufacturing the hexagonal cell honeycomb of each shape is strictly processed into a regular hexagon, and the processing accuracy is ± 0.5 in angle. Less than a degree.

  However, in the actually manufactured hexagonal cell honeycomb, there was a part where the cell was partially deformed so as to be slightly crushed in the C-axis direction. This is because during extrusion molding, the raw material passes through the slit of the die to form a honeycomb structure, but when the hexagonal cell honeycomb is received by the jig on its outer peripheral surface after extrusion molding, the outer wall is weighed by the weight of the hexagonal cell honeycomb. It is considered that the cause is that the cell passage partition walls at the outer periphery are deformed.

  This applies not only to cordierite hexagonal cell honeycombs but also to extrusion molding of ceramic materials such as alumina, mullite, silicon nitride, silicon carbide, and zirconia, or sintered metal materials such as heat-resistant stainless steel materials. it is conceivable that. That is, it is presumed that, when extruding a mixture obtained by mixing and kneading water and a binder with the raw material powder, deformation of the partition walls of the hexagonal cell honeycomb occurs regardless of the raw material.

  By the way, since the rigidity of the hexagonal cell honeycomb is theoretically isotropic, it was expected that the B-axis compression fracture strength and the C-axis compression fracture strength would be naturally the same. The samples with lower breaking strength were more. On the other hand, when examining the vicinity of the fracture in the sample after the isostatic fracture strength test, it was observed that in the sample having a relatively low isostatic fracture strength, some cells were deformed as if slightly collapsed in the C-axis direction. Was. Therefore, it is considered that the crushing deformation of the cell shape in the C-axis direction affects the C-axis compression fracture strength.

  In other words, since the isostatic fracture strength test applies pressure to the outer peripheral surface of the hexagonal cell honeycomb, it is easily inferred that the isostatic fracture strength is strongly related to each of the compressive fracture strengths of the B axis and the C axis. From the test results, it is considered that the hexagonal cell honeycomb is more likely to be deformed and broken by the load in the C-axis direction than in the B-axis.

  Therefore, from the test results in Table 2, the relationship between the B-axis and C-axis compressive breaking strengths and the isostatic breaking strength was investigated. As a result, as shown in FIGS. 3 to 5, there is no clear relationship between the B-axis compressive breaking strength and the isostatic breaking strength, but there is a clear relationship between the C-axis compressive breaking strength and the isostatic breaking strength. A positive correlation was observed although it was unclear, and a clear positive correlation was observed between the ratio between the C-axis compression fracture strength and the B-axis compression fracture strength and the isostatic fracture strength.

  Since the catalyst carrier for purifying automobile exhaust gas usually employs a structure in which the outer peripheral surface of the carrier is gripped, the gripping surface pressure is set to a minimum guaranteed value of 0.5 MPa, preferably 1.0 MPa. The average level of isostatic strength of the catalyst carrier for purifying automobile exhaust gas is required to be 3.0 MPa or more, preferably 4.0 MPa or more. Therefore, from the test results, the lower limit value of the compressive breaking strength ratio C / B when the isostatic breaking strength exceeds 3 MPa is determined to be 0.9, and it is preferable in terms of mechanical strength that the lower limit value is not less than this value.

  Now, although the results of the thermal shock test are not described in Table 2, there was no significant difference in the range of 850 to 900 ° C. for all the honeycomb structures having various cell structures. While the exhaust gas temperature is increasing year by year and the thermal shock resistance required for the honeycomb structure is becoming severer, the thermal shock resistance is practically required to be 750 ° C or more, preferably 800 ° C or more, It was confirmed that the hexagonal cell honeycomb had the property of clearing the thermal shock resistance.

  From the above test results, it is considered that the characteristics of the B-axis compressive fracture strength, the C-axis compressive fracture strength, and the isostatic fracture strength of the hexagonal cell honeycomb are caused by the geometrical characteristic that the cell shape is hexagonal. It was considered as a parameter for universal mechanical strength characteristics independent of the manufacturing method and material. Then, in order to investigate the effect of the cell shape on the mechanical strength of the honeycomb structure, next, the partition wall thickness, the number of cells, and the sample dimensions were all the same, and the partition wall angle θ of the hexagonal cell was intentionally set to a regular hexagon. Of the cordierite-type hexagonal cell honeycomb having a hexagonal cell shape deformed in the C-axis direction by using the extrusion molding method. The ratio of the average compressive breaking strength of the shaft and the isostatic breaking strength were measured. Table 3 shows the test results.

  As the partition wall angle θ increases, the ratio of the average values of the compressive breaking strengths of the C axis and the B axis increases, and both the C axis compressive breaking strength and the isostatic breaking strength improve. On the other hand, when it became too large, a tendency to decrease was observed. For this reason, it is important to balance the compressive fracture strength of the C-axis and the B-axis to improve the isostatic fracture strength. It is possible to improve the static breaking strength. From the results of this test, the range of the partition wall angle θ is preferably in the range of 30 ° <θ <45 ° and more preferably in the range of 35 ° <θ <40 ° from the viewpoint of the isostatic fracture strength. preferable.

  In addition, when the honeycomb structure is gripped on the outer peripheral surface thereof, utilizing the fact that the C-axis compressive breaking strength becomes larger than the B-axis compressive breaking strength when the partition wall angle θ is larger than 30 °, the C-axis It is considered that a method of mainly gripping in the direction is preferable. For example, when the hexagonal cell honeycomb has an elliptical cross-sectional shape along the BC axis, it is preferable that the C-axis direction and the minor axis direction of the ellipse coincide with each other so that the gripping force is mainly received in the C-axis direction.

  Conversely, if the cell shape is a regular hexagon with a partition wall angle θ of 30 ° or less than 30 °, the B-axis compression fracture strength is higher than the C-axis, so the gripping direction is in the B-axis direction. By doing so, it is easily inferred that the reliability of the holding structure of the honeycomb structure can be improved.

  As described above, the hexagonal cell honeycomb structure of the present invention has improved mechanical strength, and when used as a catalyst carrier for purifying automobile exhaust gas, has excellent durability performance, purification performance, and excellent low pressure loss. It works. Therefore, it can be usefully used as a catalyst carrier for purifying automobile exhaust gas.

It is sectional drawing in the surface perpendicular | vertical to a cell channel | path which shows one Embodiment of the structure of the hexagonal cell honeycomb by this invention. It is explanatory drawing which shows various cell shapes, a hydraulic diameter, and the formation state of a catalyst layer. It is a graph which shows the relationship between B axis compression breaking strength and isostatic breaking strength in an example and a comparative example. It is a graph which shows the relationship between C-axis compression breaking strength and isostatic breaking strength in an example and a comparative example. It is a graph which shows the relationship between the ratio of the C-axis compression fracture strength and the B-axis compression fracture strength and the isostatic fracture strength in Examples and Comparative Examples.

Explanation of reference numerals

1 ... hexagonal cell honeycomb, 2 ... cell passage partition, 3 ... cell (hexagonal cell), 4 ... square cell, 5 ... triangle cell, 6 ... gamma alumina catalyst layer (coat layer), 7 ... apex.

Claims (7)

A honeycomb structure having a plurality of cell passage partition walls,
The cross-sectional shape of the cell is a hexagonal shape, the pair of vertexes of the hexagonal cell facing each other are connected in the cross-section, and the axis in which the hexagonal cell is symmetrical with respect to the axis is the C-axis, the direction perpendicular to the C-axis in the cross-section. Is the B axis, and the angle between one side of the hexagonal cell intersecting the C axis and the B axis is the partition wall angle (θ), the partition wall angle (θ) = 30 °, and the C-axis compression fracture of the honeycomb structure A hexagonal cell honeycomb structure, wherein the ratio (C / B) between the average strength and the average B-axis compression fracture strength is 0.9 or more.   The hexagonal cell honeycomb structure according to claim 1, wherein the isostatic fracture strength is 4 MPa or more. A honeycomb structure having a plurality of cell passage partition walls,
The cross-sectional shape of the cell is a hexagonal shape, the pair of vertexes of the hexagonal cell facing each other are connected in the cross-section, and the axis in which the hexagonal cell is symmetrical with respect to the axis is the C-axis, the direction perpendicular to the C-axis in the cross-section. Is the B axis, and the angle between one side of the hexagonal cell intersecting the C axis and the B axis is the partition wall angle (θ), and the partition wall angle (θ) range of the cell is 30 <θ <45 °. And a hexagonal cell honeycomb structure having an isostatic breaking strength of 4 MPa or more.   The hexagonal cell honeycomb structure according to claim 3, wherein the range of the partition wall angle θ is 35 <θ <40 °.   The hexagonal cell honeycomb structure according to any one of claims 1 to 4, comprising a ceramic material selected from cordierite, alumina, mullite, silicon nitride, silicon carbide, and zirconia, or heat-resistant metal steel.   The hexagonal cell honeycomb structure according to claim 5, wherein the heat-resistant metal steel is stainless steel.   The hexagonal cell honeycomb structure according to any one of claims 1 to 6, which is used as a catalyst carrier for automotive exhaust gas purification.

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