CN107269347B

CN107269347B - Sealed honeycomb structure

Info

Publication number: CN107269347B
Application number: CN201710198393.5A
Authority: CN
Inventors: 浜崎佑一; 近藤隆弘
Original assignee: NGK Insulators Ltd
Current assignee: NGK Insulators Ltd
Priority date: 2016-03-30
Filing date: 2017-03-29
Publication date: 2020-09-11
Anticipated expiration: 2037-03-29
Also published as: JP6802102B2; CN107269347A; JP2017185484A

Abstract

The invention provides a sealed honeycomb structure which can maximally inhibit reduction of an opening area, increase of a pressure loss and reduction of an ash content, and can improve mechanical strength and thermal shock resistance. In a cross section of the honeycomb structure portion perpendicular to the direction in which the cells (2) extend, inflow cells (2a) are arranged so as to surround outflow cells (2b), and the number of inflow cells (2a) is greater than the number of outflow cells (2 b); has a plurality of intersection points (4) of partition walls (1) that divide adjacent inflow cells (2a), and the diameter (D) of a circle inscribed in an intersection point (4) for an intersection point (4) that is 60% or more of the total number of intersection points (4) is the diameter (D) of a circle inscribed in the intersection point (4)₁) The diameter (D) of a circle inscribed in a partition wall (1) that divides adjacent inflow cells (2a) and outflow cells (2b)₀) Satisfy the relationship between

Description

Sealed honeycomb structure

Technical Field

The present invention relates to a plugged honeycomb structure for a wall-flow type exhaust gas filter. More particularly, the present invention relates to a plugged honeycomb structure suitable for removing particulate matter contained in exhaust gas discharged from an engine such as an automobile engine and/or purifying toxic gas such as nitrogen oxides.

Background

Internal combustion engines are used as power sources in a variety of industries. On the other hand, in exhaust gas discharged when the internal combustion engine burns fuel, particulate matter (hereinafter, sometimes referred to as "PM") such as soot and ash is discharged into the atmosphere in addition to toxic gases such as nitrogen oxides. In particular, regulations for removing PM discharged from diesel engines have become increasingly stringent worldwide, and wall-flow gas purification filters having a honeycomb structure are used as filters for removing PM (hereinafter, sometimes referred to as "DPF").

The structure of the DPF is as follows: the filter is configured such that a plurality of cells that serve as fluid flow paths are defined by porous partition walls, and the cells are alternately sealed, whereby the porous partition walls function as a filter for removing PM.

Specifically, in the honeycomb structure used in the related art, exhaust gas containing PM is made to flow in from the inlet-side end surface of the DPF, and after filtering by collecting PM with porous partition walls, the purified exhaust gas is discharged from the outlet-side end surface. However, there are problems as follows: as exhaust gas flows in, PM accumulates on the partition walls, and blocks the inflow cells of exhaust gas. If such clogging occurs, a problem arises in that the pressure loss of the DPF increases rapidly.

Therefore, in order to suppress such clogging of the cells, it is important to increase the filtration area and the aperture ratio of the influent cells. However, when the inflow cells and the outflow cells have different cross-sectional areas and cross-sectional shapes, the thickness of the partition walls forming the cells is locally reduced at portions where the partition walls intersect with each other, and the strength is sometimes reduced. Therefore, there are problems as follows: when PM deposited in the DPF is burned and removed for regeneration, thermal stress concentrates on a part of the intersection of the thinned partition walls, and cracks occur.

In order to solve such a problem, a wall-flow type DPF (patent document 1) has been proposed which is capable of suppressing pressure loss at the initial stage and at the time of PM deposition and has high thermal shock resistance by increasing the filtration area and the aperture ratio of the inflow cells and also by keeping the aperture diameter of the outflow cells large.

Patent document 1 describes a technique for preventing the occurrence of cracks by providing a substantially arc-shaped R portion at the intersection of all the thinned partition walls. In addition, a technique of preventing cracks from being generated at the intersection of the partition walls by providing a substantially arc-shaped R portion at a corner portion facing the cell has been proposed (patent document 2).

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open No. 2014-200741

Patent document 2: japanese patent laid-open publication No. 2003-269131

Disclosure of Invention

Problems to be solved by the invention

However, for example, as in the conventional DPF shown in fig. 5, the intersection point portion of the partition walls where the apexes of the 4 inflow cells are concentrated is a structure in which stress is easily concentrated. Therefore, when the DPF is used as a wall-flow type gas purification filter in an exhaust system of an automobile engine, thermal stress may be generated by rapid heating and rapid cooling due to PM combustion (for example, soot combustion) in addition to vibration during running of the automobile. When such thermal stress occurs, there is a problem that the possibility of cracks occurring in the DPF is further increased.

Fig. 6 shows a schematic diagram of typical cracks of a conventional DPF. Cracks connecting the apexes of the inflow cells are considered to have a small influence on soot leakage. However, if the crack develops and reaches the outflow cells, soot may leak out, and therefore, it is necessary to prevent such a phenomenon. Fig. 5 is a plan view schematically showing an inflow-side end surface of a conventional cell-type plugged honeycomb structure. Fig. 6 is an enlarged view of the conventional plugged honeycomb structure of fig. 5, and schematically shows a representative crack.

As a method for preventing the occurrence of the cracks, conventionally, as disclosed in patent document 2, cell reinforcement is performed. However, in the case where the reinforcement portions are provided at the intersection portions of all the partition walls as in the conventional art, although the problem of occurrence of cracks can be solved, the opening area of the cells is reduced, and therefore, there is a problem that the pressure loss increases and the deposition capacity (Ash capacity) of Ash (Ash) decreases. Further, the conventional DPF has a drawback that the Light-off property (Light-off performance) is deteriorated because the heat capacity is increased. The light-off characteristic refers to a temperature characteristic exhibited by the purification performance of the catalyst supported on the DPF.

The present invention has been made in view of the problems of the prior art. The invention provides a sealed honeycomb structure which can maximally inhibit reduction of an opening area, increase of pressure loss and reduction of ash content, and simultaneously improve mechanical strength and thermal shock resistance.

Means for solving the problems

According to the present invention, there is provided a plugged honeycomb structure as shown below.

[1] A plugged honeycomb structure comprising:

a honeycomb structure section having porous partition walls defining a plurality of cells extending from an inflow end face to an outflow end face and serving as fluid flow paths,

an inflow-side plugging portion disposed at an opening portion of a predetermined inflow cell in the outflow-side end face, and

an outflow-side plugging portion disposed in an opening of the remaining outflow cells on the inflow-side end surface,

in a cross section of the honeycomb structure portion perpendicular to an extending direction of the cells, the inflow cells are arranged so as to surround the outflow cells, and the number of the inflow cells is larger than the number of the outflow cells,

has a plurality of intersection parts of partition walls for dividing adjacent inflow cells,

a diameter D of a circle inscribed in the intersection points, the diameter D being 60% or more of the total number of the intersection points₁A diameter D of a circle inscribed in a partition wall dividing the adjacent inflow cells and the adjacent outflow cells₀The relationship therebetween satisfies the following formula (1),

formula (1):

[2] the plugged honeycomb structure according to the above [1],

a diameter D of a circle inscribed in the intersection point section for the total number of the intersection point sections₁A diameter D of a circle inscribed in a partition wall dividing the adjacent inflow cells and the adjacent outflow cells₀The relationship therebetween satisfies the above expression (1).

[3]As described in [1]]Or [2]]Is described inThe plugged honeycomb structure of (1), wherein a diameter D of a circle inscribed in the inflow cells and tangent to the partition walls on the intersection point side of the inflow cells₂0.20-0.80 mm.

[4]As described in [1]]～[3]In any one of the plugged honeycomb structures described in any one of the above, the diameter D of the circle inscribed in the intersection point portion of the partition walls that partition the adjacent inflow cells is only at the intersection point portion₁A diameter D of a circle inscribed in a partition wall dividing the adjacent inflow cells and the adjacent outflow cells₀The relationship therebetween satisfies the above expression (1).

Effects of the invention

The plugged honeycomb structure of the present invention is selectively provided with reinforcing portions only at corners of intersection portions of partition walls where apexes of a plurality of inflow cells are gathered. This can improve the mechanical strength and thermal shock resistance of the DPF while minimizing the reduction in the opening area, the increase in the pressure loss, the reduction in the ash content, and the deterioration in the light-off characteristics.

Drawings

Fig. 1 is a perspective view of a plugged honeycomb structure according to an embodiment of the present invention.

Fig. 2 is a plan view schematically showing a part of an inflow-side end face of the plugged honeycomb structure shown in fig. 1.

Fig. 3 is a sectional view taken along line a-a' of fig. 2.

Fig. 4 is a plan view schematically showing an enlarged view of the inflow-side end surface of fig. 2.

Fig. 5 is a plan view schematically showing an inflow-side end surface of a conventional cell-type plugged honeycomb structure.

Fig. 6 is an enlarged view of the conventional plugged honeycomb structure of fig. 5, and schematically shows a representative crack.

Fig. 7 is an enlarged view of the conventional plugged honeycomb structure of fig. 5, and is a view illustrating circles inscribed in the intersection points.

Description of the symbols

1: partition wall, 2: cell, 2 a: inflow cells, 2 b: outflow cell, 3: plugging portion, 3 a: inflow-side blind hole portion, 3 b: outflow-side-blind hole portion, 4: intersection partAnd 6 a: inflow-side end face, 6 b: outflow side end face, 7: cellular unit, 8: bonding layer, 9: honeycomb structure portion, 11: outer peripheral wall, 100: plugged honeycomb structure, C: cracks, D₀、D₁: the diameter of the circle.

Detailed Description

Hereinafter, embodiments of the present invention will be described. However, the present invention is not limited to the following embodiments. Therefore, it is to be understood that the following embodiments may be modified, improved, etc. as appropriate based on the general knowledge of those skilled in the art without departing from the spirit of the present invention.

Fig. 1 to 4 are views schematically showing a plugged honeycomb structure according to an embodiment of the present invention. Here, the plugged honeycomb structure 100 of the present embodiment may be a unit-type honeycomb structure in which a plurality of honeycomb cells are joined to each other, or an integrated honeycomb structure in which partition walls and an outer peripheral wall are integrally formed. Fig. 1 is a perspective view of a plugged honeycomb structure according to an embodiment of the present invention. Fig. 2 is a plan view schematically showing a part of an inflow-side end face of the plugged honeycomb structure shown in fig. 1. Fig. 3 is a sectional view taken along line a-a' of fig. 2. Fig. 4 is a plan view schematically showing an enlarged view of the inflow end face 6a of fig. 2.

The plugged honeycomb structure 100 of the present embodiment has honeycomb structural portions 9, inflow side plugs 3a, and outflow side plugs 3 b. The honeycomb structure portion 9 is constituted by a plurality of honeycomb cells 7. Each of the plurality of honeycomb cells 7 has porous partition walls 1 defining a plurality of

cells

2a and 2b extending from the inlet end surface 6a to the outlet end surface 6b and serving as fluid flow paths. A bonding layer 8 is disposed between the side surfaces of the plurality of honeycomb cells 7, and the honeycomb structure portion 9 is formed by bonding the plurality of honeycomb cells 7 via the bonding layer 8. An outer peripheral wall 11 is disposed on the outer periphery of the honeycomb structure portion 9 so as to surround a joined body formed by joining the plurality of honeycomb cells 7.

The inflow-side plugging portion 3a is disposed at an opening portion of a predetermined inflow cell 2a in the outflow-side end surface 6 b. The outflow-side plugging portion 3b is disposed in the opening of the remaining outflow cells 2b in the inflow-side end surface 6 a.

In the plugged honeycomb structure 100, the inflow cells 2a are arranged so as to surround the outflow cells 2b in a cross section of the honeycomb structure portion 9 perpendicular to the extending direction of the cells 2. The plugged honeycomb structure 100 is configured such that the number of inflow cells 2a is greater than the number of outflow cells 2 b. The plugged honeycomb structure 100 has a plurality of intersection portions 4 of partition walls 1 that partition adjacent inflow cells 2 a. The plugged honeycomb structure 100 has the following configuration with respect to 60% or more of the total number of intersection portions 4 of the partition walls 1 that partition adjacent inflow cells 2 a. First, the diameter D of the circle inscribed in the intersection 4₁Diameter D of a circle inscribed in partition wall 1 dividing adjacent inflow cells 2a and outflow cells 2b₀The relationship therebetween satisfies the following formula (1). Here, "intersection 4 of partition walls 1 that partition adjacent inflow cells 2 a" means "intersection 4 at which partition walls 1 that partition adjacent inflow cells 2a intersect. That is, the "intersection point portion 4 of the partition wall 1 that partitions the adjacent inflow cells 2 a" means a portion where the partition wall 1 extending with the intersection point as a base point is formed by the partition wall 1 that partitions only the adjacent inflow cells 2 a. Hereinafter, unless otherwise specified, the term "intersection 4" refers to "intersection 4 of partition walls 1 that divide adjacent inflow cells 2 a.

Formula (1):

here, the present embodiment will be described with reference to fig. 4. The arrangement of the inflow cells 2a so as to surround the outflow cells 2b means a state in which a plurality of inflow cells 2a are arranged so as to surround one outflow cell 2b, for example. Note that, in some cases, the inflow cells 2a are not arranged so as to surround the outflow cells 2b with respect to the cells 2 arranged on the outermost periphery of the inflow-side end surface 6a of the plugged honeycomb structure 100. In each of the cells 7, the inflow cells 2a may not be disposed so as to surround the outflow cells 2b with respect to the cells 2 disposed on the outermost periphery. Here, in fig. 4, the outflow cells 2b having a quadrangular cell shape are surrounded by the pentagonal inflow cells 2a having a cell shape smaller than that of the outflow cells 2 b. The cell shape of the outlet cells 2b and the cell shape of the inlet cells 2a are not particularly limited, and may be any shape as long as the outlet cells 2b can be arranged so as to be surrounded by the inlet cells 2 a. For example, as the cell shape, a polygon such as a quadrangle, a pentagon, and a hexagon can be considered, but the cell shape is not limited to these. Further, the sizes (in other words, the cross-sectional areas of the cells) of the 1 outflow cell 2b and the 1 inflow cell 2a may be the same or different. Here, the "cell shape" refers to a shape of a cell in a cross section perpendicular to an extending direction of the cell of the honeycomb structural portion.

The intersection 4 of the partition walls 1 that divide the adjacent inlet cells 2a means the intersection 4 of the partition walls 1 that divide the plurality of inlet cells 2a arranged so as to surround the outlet cells 2 b. As shown in fig. 1 and 2, the shape of the inflow cells 2a may be partially collapsed in the vicinity of the outer peripheral wall of the plugged honeycomb structure 100. The number of inflow cells 2a having such a cell shape that is partially collapsed is counted as one inflow cell 2 a.

Then, the diameter D of the circle inscribed in the intersection 4₁As shown in fig. 4, the diameter of a circle inscribed in the intersection 4 of the partition wall 1. The "circle inscribed in the intersection 4" means an inscribed circle that is tangent to the majority of the inflow cells 2a facing the intersection 4 at the intersection 4 of the partition walls 1 and that is tangent to the majority of the inflow cells 2 a. Further, the diameter D of the circle inscribed in the intersection 4₁"if there are a plurality of inscribed circles tangent to the majority of the inflow cells 2a, the diameter of the inscribed circle having the largest diameter is set.

Further, the diameter D of a circle inscribed in the partition wall 1 dividing the adjacent inflow cells 2a and outflow cells 2b₀As shown in fig. 4, the diameter of a circle inscribed in the partition wall 1 other than the intersection of the partition walls defining the inlet cells 2a and the outlet cells 2b is defined. In other words, it means the diameter of a circle circumscribed with the portions of the inflow cells 2a and the outflow cells 2b opposite to each other except for the corners. Hereinafter, the term "may be used to define adjacent inflow openingsDiameter D of circle inscribed in partition wall 1 of cell 2a and outflow cell 2b₀"simply" diameter D of circle inscribed in partition wall 1₀". Diameter D of circle inscribed in partition wall 1 dividing adjacent inflow cells 2a and outflow cells 2b₀The calculation can be performed as follows. First, in the inflow-side end face 6a of the plugged honeycomb structure 100, 5 sites of the partition walls 1 that partition the adjacent inflow cells 2a and outflow cells 2b are randomly selected. Then, inscribed circles are virtually drawn for the 5 selected partition walls 1, and the diameters of these inscribed circles are obtained. The average of the diameters of the 5 inscribed circles was taken as the diameter D of the circle₀。

Here, for the formula (1)

The description is given. In formula (1)

In the conventional plugged honeycomb structure without the reinforcing portion as shown in fig. 7, the diameter of a circle inscribed in the intersection 4 of the partition walls 1 that define the inflow cells 2a is shown. Fig. 7 is an enlarged view of the conventional plugged honeycomb structure of fig. 5, and is a view illustrating circles inscribed in the intersection points. The plugged honeycomb structure 100 of the present embodiment is characterized in that the diameter D of a circle inscribed in the intersection 4 of the partition walls 1 that divide adjacent inflow cells 2a₁The diameter of a circle inscribed in the intersection point portion at the same position is larger than that of a conventional plugged honeycomb structure in which the reinforcing portion is not provided.

When the total number of the intersection portions 4 is 100%, the number of the intersection portions 4 satisfying the condition of the above expression (1) is at least 60%, and more preferably 100%. If the number of the intersection portions 4 satisfying the above condition is less than 60%, the thermal shock resistance is significantly reduced.

If in the above formula (1)

If the value of (b) is less than 1.20, sufficient thermal shock resistance cannot be obtained. Furthermore, if in the above formula (1)

If the value of (b) exceeds 1.80, the pressure loss increases, the light-off characteristics deteriorate, and the ash content decreases.

In addition, only in the intersection 4 of the partition walls 1 that divide the adjacent inflow cells 2a, the diameter (D) of the circle inscribed in the intersection 4₁) Diameter (D) of circle inscribed in partition wall 1 dividing adjacent inflow cells 2a and outflow cells 2b₀) The relationship therebetween satisfies the formula (1). This is different from the conventional technique in which the reinforcement portions are provided at all the intersection points of the partition walls, and means, as shown in fig. 1 to 4: in the present invention, the reinforcement portion is provided only at the intersection 4 of the partition walls 1 that divide the adjacent inflow cells 2 a. As a method for producing such a reinforcing portion, for example, a method of changing the shape of a die at the time of extrusion molding by a conventionally known method can be cited. The reinforcing portion may be formed by pouring the slurry into a predetermined corner portion of the predetermined inlet cells 2a to form a corner portion having R. The phrase "having a reinforcing portion" means that the intersection 4 of the partition walls 1 that divide adjacent inflow cells 2a satisfies the relationship of the expression (1). Note that, the diameter (D) of the circle inscribed in the intersection 4 only in the intersection 4 of the partition walls 1 that divide the adjacent inflow cells 2a is described above₁) Diameter (D) of circle inscribed in partition wall 1 dividing adjacent inflow cells 2a and outflow cells 2b₀) The phrase "the relationship between the intersection points satisfies the expression (1)" means that the relationship between the intersection points may not satisfy the expression (1) for the other intersection points. Here, the relation not satisfying the above expression (1) means that, for example, the relation can be the one according to the conventional art

In the context of (a) or (b),

may also be less than 1.20. However, it should be noted that the above equation (1) does not include manufacturing tolerances.

Furthermore, internally cut in the inlet cells 2a and connected withDiameter D of a circle that is tangent to partition wall 1 on the side of intersection 4 of inflow cells 2a₂Preferably 0.20 to 0.80 mm. Here, the diameter D of a circle inscribed in the inlet cells 2a and tangent to the partition wall 1 on the intersection 4 side of the inlet cells 2a₂As shown in fig. 4. As shown in fig. 4, diameter D₂Is a circle that is present in the inflow cells 2a and is tangent to the partition wall 1 of the intersection 4. The diameter of such a circle is the "diameter D" mentioned above₂". Here, if the diameter D is₂If the thickness is less than 0.20mm, sufficient thermal shock resistance may not be obtained.

As the plugged honeycomb structure 100 of the present embodiment, a structure having the honeycomb structure portion 9 as described below can be given as a suitable example. For the inflow cells 2a, the geometric surface area GSA is preferably 10-30 cm²/cm³More preferably 12 to 18cm²/cm³. Here, the "geometric surface area GSA" described above is a value (S/V) obtained by dividing the entire internal surface area (S) of the inflow cells 2a by the entire volume (V) of the honeycomb structure portion 9. In general, the larger the filtration area of the filter, the more the PM can be deposited on the partition walls, and therefore, the pressure loss of the plugged honeycomb structure can be suppressed to a low level by limiting the value range of the geometric surface area GSA described above. Therefore, if the geometric surface area GSA of the inflow cells 2a is less than 10cm²/cm³This is not preferable because the pressure loss increases when PM is accumulated. Further, if it is larger than 30cm²/cm³This is not preferable because the initial pressure loss increases.

In the plugged honeycomb structure 100 of the present embodiment, the cell cross-sectional aperture ratio of the inflow cells 2a is preferably 20 to 70%, and more preferably 25 to 65%. If the cell cross-sectional opening ratio of the inflow cells 2a is less than 20%, the initial pressure loss increases, which is not preferable. If the flow rate exceeds 70%, the filtration flow rate increases, the PM collection efficiency decreases, and the strength of the partition walls 1 becomes insufficient, which is not preferable. Here, the "cell cross-sectional aperture ratio of the inflow cells 2 a" means a ratio in a cross section perpendicular to the central axis direction of the honeycomb structural portion 9 as described below. That is, the ratio of "the total of the cross-sectional areas of the inflow cells 2 a" to the total of "the total cross-sectional areas of the partition walls 1 forming the honeycomb structural portion 9" and "the total of the cross-sectional areas of all the cells 2 (all the inflow cells 2a and the outflow cells 2 b)" is referred to.

In the plugged honeycomb structure 100 of the present embodiment, the hydraulic diameters of the plurality of cells 2 (inflow cells 2a and outflow cells 2b) are preferably 0.5 to 2.5mm, and more preferably 0.8 to 2.2 mm. If the hydraulic diameter of each of the plurality of cells is less than 0.5mm, the initial pressure loss increases, which is not preferable. Further, if it exceeds 2.5mm, the contact area between the exhaust gas and the partition wall 1 decreases, and the purification efficiency decreases, which is not preferable. Here, the hydraulic diameter of each of the plurality of cells is a value calculated by 4 × (cross-sectional area)/(circumferential length) based on the cross-sectional area and circumferential length of each cell 2. The cross-sectional area of the cells 2 is an area of a cell shape (in other words, a cross-sectional shape) appearing in a cross section perpendicular to the central axis direction of the honeycomb structure portion 9. The perimeter of the cell means the length of the periphery of the cross-sectional shape of the cell (in other words, the length of the closed line surrounding the cross-section).

In view of the tradeoff (trade off) between the initial pressure loss, the pressure loss at the time of PM deposition, and the collection efficiency, the following configuration can be cited as a suitable example of the plugged honeycomb structure 100 of the present embodiment. Preferably, the following are simultaneously satisfied: the geometric surface area GSA of the inflow cells 2a is 10-30 cm²/cm³The opening ratio of the cross section of the inflow cells 2a is 20 to 70%, and the hydraulic diameters of the plurality of cells 2 are 0.5 to 2.5 mm. Further, it is more preferable to satisfy both: the geometric surface area GSA of the inflow cells 2a is 12-18 cm²/cm³The opening ratio of the cross section of the inflow cells 2a is 25 to 65%, and the hydraulic diameters of the plurality of cells 2 are 0.8 to 2.2mm, respectively.

In the plugged honeycomb structure 100 of the present embodiment, a catalyst may be supported on the partition walls 1. The catalyst is supported on the partition walls 1 by coating the surfaces of the partition walls 1 and the inner walls of the pores formed in the partition walls 1 with the catalyst. The kind of the catalyst includes SCR catalysts (zeolite, titania, vanadium), three-way catalysts containing at least 2 noble metals of Pt, Ph, and Pd and at least 1 noble metal of alumina, ceria, and zirconia, and the like. By supporting such a catalyst, NOx, CO, CH, and the like contained in exhaust gas discharged from a direct injection gasoline engine, a diesel engine, and the like can be detoxified, and PM deposited on the surfaces of the partition walls 1 can be easily burned and removed by the action of the catalyst.

The method of supporting the catalyst on the plugged honeycomb structure 100 of the present embodiment is not particularly limited, and a method generally performed by those skilled in the art may be employed. Specifically, there may be mentioned a method in which the catalyst slurry is water-coated (Wash coat), dried, and fired.

The method for producing the plugged honeycomb structure 100 of the present embodiment is not particularly limited, and can be produced, for example, by the following method. A plastic clay is prepared by adding a binder to a material selected from the above-mentioned suitable materials as a raw material powder of the honeycomb structure portion 9, and further adding a surfactant and water. As the raw material powder, for example, silicon carbide powder can be used. Examples of the binder include methyl cellulose and hydroxypropoxymethyl cellulose. The kneaded material is extrusion-molded to obtain a molded body having the honeycomb structural portion 9 having the partition walls 1 and cells 2 of a predetermined cross-sectional shape. It is dried by, for example, microwaves and hot air. Then, the plugging portions 3 (the inflow side plugging portions 3a, the outflow side plugging portions 3b) are arranged by plugging with the same material as that used for manufacturing the honeycomb structural portion 9, and are further dried. Then, for example, the plugged honeycomb structure 100 of the present embodiment can be obtained by heating and degreasing the honeycomb structure in a nitrogen atmosphere, and then firing the honeycomb structure in an inert atmosphere such as argon. The firing temperature and firing atmosphere vary depending on the raw materials, and those skilled in the art can select the firing temperature and firing atmosphere optimal for the selected material.

In the present embodiment, the material of the partition walls and the outer peripheral wall constituting the honeycomb structural portion 9 is not particularly limited, but from the viewpoint of strength, heat resistance, durability, and the like, various ceramics, metals, and the like, of which oxides or non-oxides are preferable as the main component. Examples of the ceramics include cordierite, mullite, alumina, spinel, silicon carbide, silicon nitride, and aluminum titanate. Examples of the metal include Fe-Cr-Al based metals and metal silicides. It is preferable to use 1 or 2 or more selected from these materials as the main component. From the viewpoint of high strength and high heat resistance, 1 or 2 or more selected from the group consisting of alumina, mullite, aluminum titanate, cordierite, silicon carbide and silicon nitride are particularly preferable as the main component. Here, "as a main component" means at least 50 mass% or more, preferably 70 mass% or more, and more preferably 80 mass% or more constituting the honeycomb structure portion 9.

The material of the plugging portion 3 (the inflow side plugging portion 3a and the outflow side plugging portion 3b) is also not particularly limited, and is preferably the same as the honeycomb-structure portion 9.

The thickness of the partition wall 1 is preferably 100 to 410 μm, and more preferably 150 to 360 μm. If the thickness is thinner than 100 μm, the strength of the honeycomb substrate may be lowered. If the thickness is larger than 410. mu.m, the trapping performance may be deteriorated and the pressure loss may be increased. In addition, when treating exhaust gas discharged from a diesel engine, since the amount of PM in the exhaust gas discharged from the diesel engine is relatively large, the number of cells tends to be reduced (the cell density tends to be reduced). Therefore, in order to balance the strength and the trapping performance more favorably, the thickness of the partition wall 1 is preferably 150 to 360 μm. The thickness of the partition wall is a value measured by a method of observing an axial cross section of the honeycomb substrate with a microscope.

Examples

(example 1)

80 parts by mass of silicon carbide powder and 20 parts by mass of Si powder were mixed to obtain a mixed powder. A binder, a pore-forming material and water were added to the mixed powder to obtain a molding material. Next, the molding material was kneaded to prepare a cylindrical clay.

Next, the kneaded material was extrusion-molded using a predetermined extrusion mold, and a honeycomb molded body having a shape in which the periphery of the square outlet cells was surrounded by pentagonal inlet cells was obtained. 16 honeycomb formed bodies were produced.

Subsequently, the honeycomb formed body was dried by a microwave dryer and further completely dried by a hot air dryer, and then both end faces of the honeycomb formed body were cut and adjusted to a predetermined size. Next, a film is attached so as to cover the entire inflow-side end face of the honeycomb formed body, and a perforated portion is provided in a position of the film corresponding to a cell opening portion serving as an outflow cell. Next, the end portion of the honeycomb formed body to which the thin film is attached is immersed in a slurry-like plugging material containing a ceramic material, and the plugging material is filled into the outlet cells in the end surface of the inlet side. Further, the outflow-side end surface is similarly filled with the plugging material in the inlet cells.

Subsequently, the honeycomb dried body was heated at 400 ℃ for 5 hours to degrease the honeycomb, and further heated at 1450 ℃ for 2 hours under an argon atmosphere to be fired, thereby obtaining a honeycomb fired body. The honeycomb fired body has a quadrangular prism shape as a whole.

Next, the obtained 16 honeycomb fired bodies were adjacently disposed so that side surfaces thereof were opposed to each other, and in this state, the honeycomb joined bodies were joined by a joining material to produce honeycomb joined bodies. The honeycomb joined body was produced by joining 4 honeycomb fired bodies arranged in the longitudinal direction, 4 honeycomb fired bodies arranged in the transverse direction, and 16 honeycomb fired bodies arranged in total on the end face thereof.

Next, the outer peripheral portion of the honeycomb joined body was machined by grinding to make the cross section of the honeycomb joined body perpendicular to the extending direction of the cells circular. Then, an outer peripheral coating material containing a ceramic material is applied to the outermost periphery of the honeycomb joined body subjected to the grinding process.

Thus, a plugged honeycomb structure of example 1 was produced. The obtained plugged honeycomb structure was a cylinder having a cross section perpendicular to the central axis of 143.8mm in diameter and 152.4mm in length in the central axis direction. The thickness of the partition wall is 0.3mm, and the cell density is 208 cells/cm²。

Table 1 shows the thickness (mm) of the partition wall, a (mm), b (mm), and the cell density (cells/cm)²). Here, a (mm) is the length of the range denoted by symbol a in fig. 4. That is, a (mm) is a distance between 2 partition walls 1 arranged in parallel, which divide inflowThe cells 2a and the outflow cells 2b are opposed to each other with 1 outflow cell 2b interposed therebetween. In addition, b (mm) is the length of the range indicated by symbol b in fig. 4. That is, b (mm) is a distance between 2 partition walls 1 arranged in parallel, which divide the inflow cells 2a and the outflow cells 2b and face each other with 1 inflow cell 2a interposed therebetween. In a (mm) and b (mm), the distances between 2 partition walls 1 are the distances between 2 partition walls 1 from the midpoint in the thickness direction of each partition wall 1.

Further, in table 1, "the diameter D of a circle inscribed in a partition wall dividing the inflow cells and the outflow cells₀(mm) "," diameter D of a circle inscribed in an intersection of partitions dividing inflow cells₁(mm) "and"

The value of (d). Table 1 shows "the ratio of the intersection satisfying the formula (1)". Here, the "ratio of the intersection portions satisfying the expression (1)" means that the intersection portions of the partition walls that divide the adjacent inflow cells satisfy the expression (1)

The ratio of the number of intersection parts in the relationship (2).

In table 1, "diameter D of a circle inscribed in the inflow cells and tangent to the partition wall on the intersection point side₂(mm)”。

Hereinafter, in this embodiment, the "diameter D of a circle inscribed in a partition wall dividing the inflow cells and the outflow cells" may be set₀(mm) "diameter D of the inscribed circle₀(mm) ". Further, the diameter D of a circle inscribed in "the intersection point portion of the partition walls dividing the inflow cells may be" a diameter D of a circle inscribed in "the intersection point portion of the partition walls dividing the inflow cells₁(mm) "diameter D of the inscribed circle₁(mm) ". Further, the diameter D of a circle inscribed in the inflow cells and tangent to the partition wall on the intersection point side may be "a diameter D of a circle inscribed in the inflow cells₂(mm) "diameter D of the inscribed circle₂(mm)”。

TABLE 1

TABLE 2

(examples 2 to 12)

Changing the diameter D of the "inscribed circle" as shown in Table 1 or Table 2₀(mm) "," diameter D of inscribed circle₁(mm) "," diameter D of inscribed circle₂(mm) "and" the ratio of the intersection satisfying the formula (1) ", the plugged honeycomb structures of examples 2 to 12 were produced.

Comparative examples 1 to 4

Changing the diameter D of the "inscribed circle" as shown in Table 1 or Table 2₀(mm) "," diameter D of inscribed circle₁(mm) "," diameter D of inscribed circle₂(mm) "and" the ratio of the intersection satisfying the formula (1) ", plugged honeycomb structures of comparative examples 1 to 4 were produced.

The plugged honeycomb structure of comparative example 1 was constructed except for the intersection portions of the partition walls that demarcated the adjacent inflow cells

Except for this, a plugged honeycomb structure was produced in the same manner as in example 1. That is, of the plugged honeycomb structure of comparative example 1 "

The value of (A) is 1.00.

The plugged honeycomb structures of examples 1 to 12 and comparative examples 1 to 4 were evaluated for "thermal shock resistance", "light-off characteristics", "inlet opening ratio" and "pressure loss at PM deposition" in the following manner. The results are shown in tables 1 and 2.

[ thermal shock resistance ]

The thermal shock resistance was evaluated by a heating vibration test. Specifically, the distance from the end surface on the outflow side of the prepared plugged honeycomb structure was held by MAFTEC (trade name) manufactured by mitsubishi resin corporation to be 130 mm. To be held and flowed out in such a wayThe plugged honeycomb structure on the side end face was subjected to a test for 100 hours while applying vibration of a vibration frequency of 100Hz and an acceleration of 30G and passing air heated by a propane burner. The conditions for heating the heated air in the vibration heating test were: flow 2Nm³Min, temperature 150-800 deg.C (20 min for 1 cycle). After the heating vibration test, it was visually confirmed whether or not the partition walls of the plugged honeycomb structure were damaged. When no breakage was confirmed in the partition walls of the plugged honeycomb structure, the evaluation was "good", when slight breakage was confirmed, the evaluation was "ok", and when severe breakage was confirmed, the evaluation was "not ok". The results are shown in tables 1 and 2.

[ light-off characteristics (time (seconds) to reach 200 ℃) ]

The light-off characteristics were evaluated as follows: a plugged honeycomb structure was used as a DPF, and combustion gas at 400 ℃ was introduced into the DPF, and the time until the outlet-side end of the DPF reached 200 ℃ was measured. Specifically, first, a ceramic non-heat-expandable gasket as a holding member was wound around the outer periphery of the obtained plugged honeycomb structure, and the resultant was press-fitted into a can body made of SUS409 stainless steel to obtain a can body. Further, a K-type sheathed thermocouple was provided at the outflow-side end of the can filling structure. Then, combustion gas of 400 ℃ was flowed in by combustion of diesel fuel, the temperature of a thermocouple provided in advance was monitored, and the time (seconds) until the temperature reached 200 ℃ was measured. As the diesel fuel, light diesel oil was used. In the evaluation of the light-off characteristics, the time (seconds) to 200 ℃ of the plugged honeycomb structure of comparative example 1 was used as a reference (Base) and evaluated as follows. When the time (sec) to 200 ℃ was +0.5 sec or less based on the reference, it was regarded as "good". The time (seconds) to 200 ℃ is more than +0.5 seconds and not more than +1 second based on the reference, and the record is "ok". When the time (seconds) to reach 200 ℃ exceeds +1 second relative to the reference, it is regarded as "impossible".

[ Inlet opening ratio ]

The ratio (%) of the area occupied by the inflow cells in the inflow-side end face with respect to the cross-sectional area of the plugged honeycomb structure was measured. The ratio (%) of the area was taken as the inlet opening ratio (%) of the plugged honeycomb structure. In the evaluation of the inlet opening ratio, the inlet opening ratio (%) of the plugged honeycomb structure of comparative example 1 was set as a standard (Base) and evaluated as follows. When the inlet opening ratio (%) was + 1% or less based on the standard, it was regarded as "good". When the inlet opening ratio (%) is more than 1% and + 2% or less with respect to the reference, it is regarded as "ok". When the inlet opening ratio (%) exceeded + 2% with respect to the reference, it was regarded as "impossible".

[ pressure loss at PM deposition ]

The pressure loss at the time of PM deposition of the plugged honeycomb structure was measured based on the pressure difference between the inflow side and the outflow side when the soot deposition amount was 4 g/L. Specifically, first, light diesel oil is burned in an oxygen-deficient state to generate combustion gas in which soot is generated. Further, the amount of soot generated was 10g/h, and the flow rate was 2.4Nm³The combustion gas at a temperature of 200 ℃ per minute was adjusted by adding dilution air, thereby producing a combustion gas containing soot for evaluating a pressure loss during PM deposition. The combustion gas containing soot is caused to flow into the plugged honeycomb structure, and pressures on the inflow side and the outflow side of the plugged honeycomb structure are measured at a time point when the soot accumulation amount in the plugged honeycomb structure reaches 4g/L, and the pressure difference is used as a pressure loss value at the time of PM accumulation in the plugged honeycomb structure. In the evaluation of the pressure loss during PM deposition, the pressure loss value of the plugged honeycomb structure of comparative example 1 was set as a reference (Base) and evaluated as follows. When the increase in the pressure loss value from the reference value is + 4% or less, it is regarded as "good". When the increase in the pressure loss value is more than + 4% and not more than + 8% from the reference value, it is regarded as "ok". When the increase in the pressure loss value exceeds + 8% with respect to the reference, it is regarded as "impossible".

(results)

As shown in tables 1 and 2, the plugged honeycomb structures of examples 1 to 12 were evaluated for all of "thermal shock resistance", "light-off characteristics", "inlet opening ratio" and "pressure loss at PM deposition", and were evaluated for "acceptable" or more. In particular, based onAs is clear from the evaluation results of the plugged honeycomb structures of examples 1 to 12 and comparative example 1, if "the diameter D of the inscribed circle₁(mm) "is greater than" the diameter D of the inscribed circle₀(mm)'

The thermal shock resistance of the plugged honeycomb structure is increased. Further, as in comparative examples 2 and 3,

when the value of (A) is other than 1.20 to 1.80, the evaluation of the "light-off characteristics" and the "inlet opening ratio" results in "impossible". Therefore, it can be seen that when

When the value of (d) is in the range of 1.20 to 1.80, all the evaluations of "thermal shock resistance", "light-off characteristics", "inlet opening ratio" and "pressure loss at PM deposition" are improved over comparative example 1.

Further, it was found that the percentage of the intersection portion satisfying the formula (1) decreases the thermal shock resistance of the plugged honeycomb structure, and when it is less than 60%, the thermal shock resistance is greatly decreased.

It can be further understood that if "diameter D of inscribed circle" is used₂(mm) "of 0.20 to 0.80mm is preferable for the evaluation of" light-off characteristics "," inlet opening ratio "and" pressure loss at the time of PM deposition ", and if it exceeds 0.80mm, the respective evaluations are lowered.

Industrial applicability of the invention

The plugged honeycomb structure of the present invention can be used as a filter for exhaust gas purification. Further, the catalyst carrier can be used as a catalyst carrier for supporting a catalyst on the partition walls of the plugged honeycomb structure of the present invention.

Claims

1. A plugged honeycomb structure comprising:

formula (1):

2. the plugged honeycomb structure as claimed in claim 1,

3. The plugged honeycomb structure as claimed in claim 1 or 2,

a diameter D of a circle inscribed in the inflow cell and tangent to the partition wall on the intersection point side of the inflow cell₂0.20-0.80 mm.

4. The plugged honeycomb structure as claimed in claim 1 or 2,

adjacent only in divisionThe diameter D of a circle inscribed in the intersection point part of the partition walls of the inflow cells₁A diameter D of a circle inscribed in a partition wall dividing the adjacent inflow cells and the adjacent outflow cells₀The relationship therebetween satisfies the above expression (1).