阅读说明：本技术 柱状蜂窝结构过滤器及其制造方法 (Columnar honeycomb filter and manufacturing method thereof ) 是由 仙藤皓一 于 2020-12-18 设计创作，主要内容包括：本发明提供一种柱状蜂窝结构过滤器及其制造方法,其有助于兼具PN高捕集效率及低压力损失。一种柱状蜂窝结构过滤器,其具备：从入口侧底面延伸至出口侧底面且入口侧底面呈开口而在出口侧底面具有封孔部的多个第一隔室、以及从入口侧底面延伸至出口侧底面且在入口侧底面具有封孔部而出口侧底面呈开口的多个第二隔室,多个第一隔室和多个第二隔室夹着多孔质隔壁而交替地相邻配置,该柱状蜂窝结构过滤器中,在各第一隔室的表面形成有陶瓷制的多孔质膜,该多孔质膜的平均膜厚T(单位：μm)为2～50μm,气孔率P(单位：％)为65～90％,平均膜厚T和气孔率P满足0.36T+60≤P≤0.75T+72的关系式。(The invention provides a columnar honeycomb structure filter and a manufacturing method thereof, which are beneficial to having both high PN collecting efficiency and low pressure loss. A columnar honeycomb filter comprising: in the columnar honeycomb filter, a plurality of first cells extending from an inlet-side bottom surface to an outlet-side bottom surface, the inlet-side bottom surface being open and the outlet-side bottom surface being open, and a plurality of second cells extending from the inlet-side bottom surface to the outlet-side bottom surface, the inlet-side bottom surface being open and the outlet-side bottom surface being open, the plurality of first cells and the plurality of second cells being alternately arranged adjacent to each other with porous partition walls interposed therebetween, a ceramic porous film is formed on the surface of each first cell, the porous film has an average film thickness T (unit:%) of 2 to 50 μm and a porosity P (unit:%) of 65 to 90%, and the average film thickness T and the porosity P satisfy a relational expression of 0.36T + 60P 0.75T + 72.)

1. A columnar honeycomb filter comprising: a plurality of first cells extending from an inlet-side bottom surface to an outlet-side bottom surface and having an opening at the inlet-side bottom surface and a plurality of second cells extending from the inlet-side bottom surface to the outlet-side bottom surface and having an opening at the inlet-side bottom surface and an opening at the outlet-side bottom surface, the plurality of first cells and the plurality of second cells being alternately arranged adjacent to each other with porous partition walls therebetween,

the cylindrical honeycomb-structure filter is characterized in that,

a ceramic porous film is formed on the surface of each first compartment, the average film thickness T of the porous film is 2-50 mu m, the porosity P is 65-90%, and the average film thickness T and the porosity P satisfy a relational expression that P is more than or equal to 0.36T +60 and less than or equal to 0.75T +72, wherein the unit of the average film thickness T is mu m, and the unit of the porosity P is P.

2. The columnar honeycomb filter according to claim 1,

the porous film has an average film thickness T of 2 to 40 μm and a porosity P of 65 to 90%, wherein the average film thickness T is in μm and the porosity P is in%.

3. The columnar honeycomb-structure filter according to claim 1 or 2,

the porous film contains 50 mass% or more of one or two or more selected from the group consisting of silicon carbide, cordierite, alumina, silica, mullite and aluminum titanate in total.

4. The columnar honeycomb structure filter according to any one of claims 1 to 3,

the porous partition walls contain 50 mass% or more of cordierite.

5. A method for manufacturing a columnar honeycomb filter, comprising the steps of:

a step of preparing a columnar honeycomb structure, the columnar honeycomb structure comprising: a plurality of first cells extending from an inlet-side bottom surface to an outlet-side bottom surface, the inlet-side bottom surface being open and the outlet-side bottom surface having a plugging portion, and a plurality of second cells extending from the inlet-side bottom surface to the outlet-side bottom surface, the inlet-side bottom surface having a plugging portion and the outlet-side bottom surface being open, the plurality of first cells and the plurality of second cells being alternately arranged adjacent to each other with porous partition walls interposed therebetween;

a step of applying an attractive force to the outlet-side bottom surface while spraying an aerosol containing ceramic particles toward the inlet-side bottom surface, and sucking the sprayed aerosol from the inlet-side bottom surface to attach the ceramic particles to the surface of the first cell, wherein the ceramic particles satisfy relational expressions of 0.1. ltoreq. D50. ltoreq.6.0 and 0.4. ltoreq. D50/(D90-D10) where D50, D10, and D90 have a unit of μm, where D50 is a median particle diameter in a volume-based cumulative particle size distribution measured by a laser diffraction scattering method, D10 is a 10% particle diameter, and D90 is a 90% particle diameter; and

and a step of subjecting the columnar honeycomb structure having the ceramic particles adhered to the surface of the first cell to a heat treatment under a condition that the columnar honeycomb structure is maintained at a maximum temperature of 1000 ℃ or higher for 1 hour or longer, thereby forming a porous film having an average film thickness T and D50 satisfying the relational expression of 4 XD 50. ltoreq. T.ltoreq.20 XD 50 on the surface of the first cell.

6. The method of manufacturing a columnar honeycomb structure filter according to claim 5,

the porous film contains 50 mass% or more of one or two or more selected from the group consisting of silicon carbide, cordierite, alumina, silica, mullite and aluminum titanate in total.

7. The method of manufacturing a columnar honeycomb structure filter according to claim 5 or 6,

the porous partition walls contain 50 mass% or more of cordierite.

8. The method for manufacturing a columnar honeycomb-structure filter according to any one of claims 5 to 7,

the porous film has an average film thickness of 2 to 50 μm.

Technical Field

The invention relates to a columnar honeycomb structure filter and a manufacturing method thereof.

Background

Exhaust gas discharged from internal combustion engines such as diesel engines and gasoline engines contains Particulate Matter such as soot (hereinafter referred to as PM). The ash is harmful to human body and limits the emission of the ash. In order to cope with exhaust gas regulations, filters represented by DPF and GPF, which filter PM such as soot by passing exhaust gas through small porous partition walls having air permeability, have been widely used.

As a filter for collecting PM, a wall-flow type columnar honeycomb structure (hereinafter also referred to as a "columnar honeycomb structure filter") is known which includes a plurality of first cells and a plurality of second cells, wherein the plurality of first cells extend from an inlet-side bottom surface to an outlet-side bottom surface in a height direction, the inlet-side bottom surface is open, and the outlet-side bottom surface has a plugged portion, and the plurality of second cells are disposed adjacent to the first cells with partition walls interposed therebetween, extend from the inlet-side bottom surface to the outlet-side bottom surface in the height direction, the inlet-side bottom surface has a plugged portion, and the outlet-side bottom surface is open.

In recent years, with the enhancement of exhaust gas regulations, stricter PM emission standards (PN regulations: number of Particle matters) have been introduced, and filters are required to have high PM trapping performance (PN high trapping efficiency). Therefore, it is proposed to additionally form a layer for trapping PM on the surface of the cell.

Patent document 1 describes a method for producing a honeycomb filter for dust collection in which at least 1 porous film having smaller pore diameters than those of a porous substrate is formed on the surface of the porous substrate, wherein 50% particle diameter (D) is supplied to the inside of cells of the porous substrate₅₀: μ m) is an average pore diameter (P: μ m) of 2/3 times or more and 1 time or less and having a particle size distribution within the range of the following formula (1), and then the slurry is formed into a film by removing moisture in the slurry through pores of the porous base material and then fired.

D₅₀/(D₅₀－D₁₀)≥1.5…(1)

(wherein, D₅₀: 50% particle diameter (. mu.m), D₁₀: 10% particle diameter (. mu.m)

Patent document 1 describes a dust collecting honeycomb filter in which at least 1 porous film having smaller pore diameters than those of a porous substrate is formed on the surface of the porous substrate, and the 1 st porous film among the porous films has a 50% particle diameter (D)₅₀: μ m) is an average pore diameter (P: μ m) of 2/3 times or more and 1 time or less and having a particle size distribution within the range of the following formula (1), and the average film thickness is 3 times or more of the 50% particle diameter.

D₅₀/(D₅₀－D₁₀)≥1.5…(1)

(wherein, D₅₀: 50% particle diameter (. mu.m), D₁₀: 10% particle diameter (. mu.m)

According to patent document 1, by forming a film using a slurry prepared from aggregate particles having an average particle diameter and a particle size distribution within a predetermined range, a honeycomb filter having a high trapping efficiency and a small pressure loss can be easily manufactured with a simple apparatus, and a large number of filters can be manufactured with uniform quality.

Patent document 2 describes a method for producing a multilayer honeycomb filter, in which a slurry of ceramic particles having an average particle diameter of 2/3 times or more and 1 time or less the average pore diameter of a substrate having a honeycomb structure is supplied to each cell of the substrate, water in the slurry is removed through pores of the substrate, the ceramic particles are attached to the surface of the substrate, and then the substrate is fired to form a coating layer on the surface of the substrate.

Patent document 2 describes a multilayer honeycomb filter for dust collection, which has a coating layer having 1 or 2 or more layers formed of ceramic particles having an average particle diameter different from that of the ceramic particles constituting a substrate on the surface of the substrate having a honeycomb structure, wherein the average particle diameter of the coating layer in contact with the substrate is 2/3 times or more and 1 time or less of the average pore diameter of the substrate, and the average thickness of the coating layer in contact with the substrate is 7 times or less of the average particle diameter of the coating layer.

According to patent document 2, the multilayer honeycomb filter has high trapping efficiency, small pressure loss, and a low pressure loss increase rate.

Patent document 3 describes forming a porous layer having a porosity of 90% or more and an average thickness of 0.5 to 30 μm. Patent document 3 describes that the influence on the pressure loss of the honeycomb structure is eliminated by the high porosity of the porous layer.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open No. 2001-79321

Patent document 2: japanese patent laid-open No. 2000-202220

Patent document 3: international publication No. 2019/089806

Disclosure of Invention

It is considered that it is effective to form a layer for collecting PM on the surfaces of the cells in terms of both high PN collection efficiency and low pressure loss of the columnar honeycomb filter. However, this layer still has room for improvement, and if the layer is improved from another viewpoint different from the conventional one, the technical options increase, and it is also advantageous in terms of being useful for expanding the possibility of further research and development in the future.

Therefore, an object of one embodiment of the present invention is to provide a columnar honeycomb structure filter that contributes to both high PN collection efficiency and low pressure loss from another viewpoint different from the conventional one. In another embodiment, the present invention has an object to provide a method for manufacturing the above columnar honeycomb filter.

The inventors of the present invention have made an intensive study to solve the above-mentioned problems, and as a result, found that, regarding a layer for trapping PM on the surfaces of cells (referred to as a "porous film" in the present invention), it is effective for maintaining a low pressure loss and improving the PN trapping efficiency that satisfy a predetermined relationship between the average film thickness and the porosity. The present invention has been completed based on this finding, and is exemplified below.

[1] A columnar honeycomb filter comprising: a plurality of first cells extending from an inlet-side bottom surface to an outlet-side bottom surface and having an opening at the inlet-side bottom surface and a plurality of second cells extending from the inlet-side bottom surface to the outlet-side bottom surface and having an opening at the inlet-side bottom surface and an opening at the outlet-side bottom surface, the plurality of first cells and the plurality of second cells being alternately arranged adjacent to each other with porous partition walls therebetween,

the cylindrical honeycomb-structure filter is characterized in that,

a ceramic porous film is formed on the surface of each first compartment, the porous film has an average film thickness T (unit: mum) of 2 to 50 μm and a porosity P (unit:%) of 65 to 90%, and the average film thickness T and the porosity P satisfy the relational expression of 0.36T + 60. ltoreq. P.ltoreq.0.75T + 72.

[2] The columnar honeycomb structure filter according to [1], wherein,

the porous film has an average film thickness T (unit: μm) of 2 to 40 μm and a porosity P (unit:%) of 65 to 90%.

[3] The columnar honeycomb structure filter according to [1] or [2],

the porous film contains 50 mass% or more of one or two or more selected from the group consisting of silicon carbide, cordierite, alumina, silica, mullite and aluminum titanate in total.

[4] The columnar honeycomb structure filter according to any one of [1] to [3],

the porous partition walls contain 50 mass% or more of cordierite.

[5] A method for manufacturing a columnar honeycomb filter, comprising the steps of:

a step of preparing a columnar honeycomb structure, the columnar honeycomb structure comprising: a plurality of first cells extending from an inlet-side bottom surface to an outlet-side bottom surface, the inlet-side bottom surface being open and the outlet-side bottom surface having a plugging portion, and a plurality of second cells extending from the inlet-side bottom surface to the outlet-side bottom surface, the inlet-side bottom surface having a plugging portion and the outlet-side bottom surface being open, the plurality of first cells and the plurality of second cells being alternately arranged adjacent to each other with porous partition walls interposed therebetween;

a step of applying an attractive force to the outlet-side bottom surface while spraying an aerosol containing ceramic particles toward the inlet-side bottom surface, and sucking the sprayed aerosol from the inlet-side bottom surface to attach the ceramic particles to the surface of the first cell, wherein the ceramic particles satisfy the relational expressions of 0.1. ltoreq. D50. ltoreq.6.0 and 0.4. ltoreq. D50/(D90-D10) when a median particle diameter in a volume-based cumulative particle size distribution measured by a laser diffraction/scattering method is D50 (unit: μm), a 10% particle diameter is D10 (unit: μm), and a 90% particle diameter is D90 (unit: μm); and

and a step of subjecting the columnar honeycomb structure having the ceramic particles adhered to the surface of the first cell to a heat treatment under a condition that the columnar honeycomb structure is maintained at a maximum temperature of 1000 ℃ or higher for 1 hour or longer, thereby forming a porous film having an average film thickness T and D50 satisfying the relational expression of 4 XD 50. ltoreq. T.ltoreq.20 XD 50 on the surface of the first cell.

[6] The method of producing a columnar honeycomb structure filter according to [5], characterized in that,

the porous film contains 50 mass% or more of one or two or more selected from the group consisting of silicon carbide, cordierite, alumina, silica, mullite and aluminum titanate in total.

[7] The method of producing a columnar honeycomb structure filter according to [5] or [6],

the porous partition walls contain 50 mass% or more of cordierite.

[8] The method for manufacturing a columnar honeycomb-structured filter according to any one of [5] to [7],

the porous film has an average film thickness of 2 to 50 μm.

Effects of the invention

The columnar honeycomb structure filter according to one embodiment of the present invention can contribute to both high PN collection efficiency and low pressure loss.

Drawings

Fig. 1 is a perspective view schematically showing an example of a columnar honeycomb filter.

Fig. 2 is a schematic cross-sectional view of an example of the columnar honeycomb filter as viewed in a cross section parallel to the direction in which the cells extend.

Fig. 3 is a schematic partially enlarged view of the columnar honeycomb-structure filter when viewed in a cross section orthogonal to the direction in which the cells extend.

Fig. 4 is a schematic view of a cross section of a columnar honeycomb filter cut out to determine the average thickness of the porous membrane.

Fig. 5 is a schematic diagram for explaining the configuration of the particle deposition apparatus according to the embodiment of the present invention.

Fig. 6 is a graph showing the relationship between the average film thickness and the porosity of the porous films in examples and comparative examples.

Fig. 7 is a graph showing the relationship between the median particle diameter (D50) of the ceramic particles in the aerosols and the average film thickness of the porous film in the examples and comparative examples.

FIG. 8 is an example of an FE-SEM photograph of the porous membrane in example 2.

Description of the symbols

100 … columnar honeycomb structure filter, 102 … outer peripheral side wall, 104 … inlet side bottom surface, 106 … outlet side bottom surface, 108 … first compartment, 109 … plugging part, 110 … second compartment, 112 … partition wall, 114 … porous film, 500 … particle attaching device, 510 … aerosol generator, 511 … nozzle, 512 … ceramic particle, 513 … cylinder, 513e … cylinder outlet, 514 … piston or screw, 515 … crushing chamber, 515e … crushing chamber outlet, 516 … rotator, 517 … gas flow path, 520 … laser diffraction type particle size distribution measuring device, 530 … gas inlet pipe, 531 … vent hole, 540 … holder, 550 … differential pressure meter, 560 … exhaust pipe 570 … blower, 580 … columnar honeycomb structure.

Detailed Description

Next, embodiments of the present invention will be described in detail with reference to the drawings. The present invention is not limited to the following embodiments, and it should be understood that: modifications, improvements and the like can be appropriately designed based on the general knowledge of those skilled in the art without departing from the scope of the present invention.

< 1. Filter with columnar Honeycomb Structure

A columnar honeycomb filter according to an embodiment of the present invention will be described. The columnar honeycomb filter can be used as a dpf (diesel Particulate filter) and a gpf (soot Particulate filter) for trapping soot, which are mounted on an exhaust line from a combustion apparatus, typically an engine mounted on a vehicle. The columnar honeycomb structure filter according to the present invention may be provided in an exhaust pipe, for example.

Fig. 1 and 2 illustrate a schematic perspective view and a schematic cross-sectional view of a columnar honeycomb filter (100), respectively. The columnar honeycomb structure filter (100) is provided with: a peripheral sidewall (102); a plurality of first cells (108) which are arranged on the inner peripheral side of the outer peripheral side wall (102), extend from the inlet side bottom surface (104) to the outlet side bottom surface (106), are open at the inlet side bottom surface (104), and have a hole closing portion (109) at the outlet side bottom surface (106); and a plurality of second cells (110) which are arranged on the inner peripheral side of the outer peripheral side wall (102), extend from the inlet side bottom surface (104) to the outlet side bottom surface (106), and have a hole closing portion (109) on the inlet side bottom surface (104) and the outlet side bottom surface (106) is open. In the columnar honeycomb structure (100), first cells (108) and second cells (110) are alternately arranged adjacent to each other with porous partition walls (112) therebetween, whereby the inlet-side bottom surface (104) and the outlet-side bottom surface (106) each have a honeycomb shape.

When an exhaust gas containing Particulate Matter (PM) such as soot is supplied to the bottom surface (104) on the inlet side on the upstream side of the columnar honeycomb filter (100), the exhaust gas is introduced into the first cell (108) and advances downstream in the first cell (108). Since the first compartment (108) has a plugging portion (109) on the outlet-side bottom surface (106) on the downstream side, the exhaust gas passes through a porous partition wall (112) that partitions the first compartment (108) and the second compartment (110) and flows into the second compartment (110). The particulate matter cannot pass through the partition wall (112), and therefore, is trapped and accumulated in the first compartment (108). After the particulate matter is removed, the clean exhaust gas flowing into the second compartment (110) travels downstream in the second compartment (110) and flows out from the outlet-side bottom surface (106) on the downstream side.

A schematic partial enlarged view when the columnar honeycomb-structure filter (100) is viewed in a cross section orthogonal to the direction in which the cells (108, 110) extend is shown in fig. 3. A porous ceramic membrane (114) is formed on the surface of each first cell (108) of the columnar honeycomb filter (100) (the same as the surface of the partition wall (112) that partitions the first cell (108)).

The porous membrane may contain a material selected from the group consisting of silicon carbide (SiC), cordierite, talc, mica, mullite, ceramic particles, aluminum titanate, alumina, silicon nitride, sialon, zirconium phosphate, zirconia, titania, and Silica (SiO)₂) One or more than two kinds of ceramics. Among them, the porous membrane preferably contains one or two or more selected from silicon carbide, cordierite, alumina, silica, mullite, and aluminum titanate in a total amount of 50 mass% or more, more preferably 70 mass% or more, and still more preferably 90 mass% or more, for reasons of cost, availability, thermal shock resistance, and peeling resistance. For the reason of the peeling resistance, the porous film particularly preferably contains 50 mass% or more of silicon carbide, more preferably 70 mass% or more, and further preferably 90 mass% or more.

In one embodiment, the porous film has an average film thickness of 2 to 50 μm. The porous membrane has an average membrane thickness of 2 μm or more, preferably 3 μm or more, and thus the advantage of being able to improve the collection efficiency can be obtained. Further, the porous membrane has an average membrane thickness of 50 μm or less, preferably 40 μm or less, more preferably 30 μm or less, and still more preferably 20 μm or less, and thus there is an advantage that an increase in pressure loss can be suppressed.

In the present specification, the average thickness of the porous membrane of the columnar honeycomb filter is measured in the following order. The direction in which the first cells of the columnar honeycomb filter extend is defined as the direction in which the coordinate axes extend, the coordinate value of the bottom surface on the inlet side is defined as 0, and the coordinate value of the bottom surface on the outlet side is defined as X. And, in the following A₁、A₂、A₃、B₁、B₂、B₃In 6, the average thickness of the porous membrane was measured in 5 fields, and the average value of the entire thickness was defined as the average thickness of the porous membrane of the columnar honeycomb structure.

A₁: a central portion in a cross section orthogonal to a direction in which the first cells extend of the columnar honeycomb-structure filter in a range of a coordinate value of 0.1X to 0.3X.

B₁: and an outer peripheral portion in a cross section orthogonal to a direction in which the first cells extend of the columnar honeycomb-structure filter in a range of a coordinate value of 0.1X to 0.3X.

A₂: a central portion in a cross section orthogonal to a direction in which the first cells extend of the columnar honeycomb-structure filter in a range of a coordinate value of 0.4X to 0.6X.

B₂: and an outer peripheral portion in a cross section orthogonal to a direction in which the first cells extend of the columnar honeycomb-structure filter in a range of a coordinate value of 0.4X to 0.6X.

A₃: a central portion in a cross section orthogonal to a direction in which the first cells extend of the columnar honeycomb-structure filter in a range of a coordinate value of 0.7X to 0.9X.

B₃: and an outer peripheral portion in a cross section orthogonal to a direction in which the first cells extend of the columnar honeycomb-structure filter in a range of a coordinate value of 0.7X to 0.9X.

The center and outer periphery of the columnar honeycomb filter when the average thickness of the porous membrane was measured were determined as follows. When the columnar honeycomb filter is viewed from a cross section orthogonal to the direction in which the first cells extend, a line segment is drawn from the center of gravity of the cross section toward the outer surface of the outer peripheral side wall, the direction in which the line segment extends is defined as the direction in which the coordinate axes extend, the coordinate value of the center of gravity is defined as 0, and the coordinate value of the outer surface of the outer peripheral side wall is defined as R. In this case, on the line segment, the range of the coordinate values 0 to 0.2R is the central portion, and the range of the coordinate values 0.7R to 0.9R is the outer peripheral portion. A plurality of such line segments are drawn on the cross section, and if the central portion and the outer peripheral portion on each line segment are collected, the ranges of the central portion and the outer peripheral portion in the cross section are obtained.

Measurement of A by the following method₁、A₂、A₃、B₁、B₂、B₃The average thickness of the porous film everywhere. A cross section parallel to the direction in which the first cells extend and parallel to a line segment from the outer surface of the outer peripheral side wall toward the center of gravity is cut out from a portion (central portion or outer peripheral portion) of the columnar honeycomb filter where the average thickness of the porous membrane is to be determined. The cross section was observed with a 3D shape measuring instrument (for example, VR-3200, manufactured by Keyence corporation) under conditions of 25 times magnification and an observation field of 12.5mm (horizontal) by 9.5mm (vertical). At this time, observation is performed such that the lateral direction of the observation field is parallel to the direction in which the first compartment extends.

A schematic view of the cut-out section is shown in fig. 4. Through the cross-sectional observation, a first compartment (108) in which the porous membrane is formed and a second compartment (110) in which the porous membrane is not formed are determined. Next, three first compartments (108) are defined in the cross-section that are adjacent at a position closest to the center. In addition, the cross section is provided with a central area (110a) (reference surface) of each of two second compartments (110) sandwiched by three adjacent first compartments (108) at the position closest to the center, and the reference surface is leveled to the maximum extent as viewed from the outline of the two areas by using image processing software (e.g., software attached to a 3D shape measuring machine VR-3200 manufactured by Keyence). After leveling, the central area (110a) of the two second compartments (110) was subjected to range designation, and the average height H2 of the area was measured. After leveling, the central region (108a) of the three first compartments (108) was designated by the range, and the average height H1 of the region was measured. The difference between the average height H1 and the average height H2 in one field of view was taken as the average thickness of the porous membrane in that field of view. The central regions (108a, 110a) are regions in the central portion, which are obtained by dividing the distance between a pair of partition walls (112) that partition each compartment into three equal parts.

In A₁、A₂、A₃、B₁、B₂、B₃The average thickness of the porous membrane was determined for any 5 visual fields, and these were defined as A₁、A₂、A₃、B₁、B₂、B₃The average thickness of the porous film everywhere. The average value of the entire structure was defined as the average film thickness of the porous film of the columnar honeycomb filter.

In one embodiment, the porous film has a porosity of 65 to 90%. In combination with the average thickness of the porous film described above, controlling the porosity of the porous film within this range is effective for achieving both high PN trapping efficiency and low pressure loss. From the viewpoint of suppressing the increase in pressure loss, the porosity of the porous film is preferably 65% or more, and more preferably 68% or more. From the viewpoint of obtaining a high PN trapping efficiency, the porosity of the porous film is preferably 90% or less, more preferably 85% or less, and still more preferably 80% or less.

A porosity of the porous film was determined by using a Field Emission Scanning Electron Microscope (FE-SEM) (model: ULTRA55, product of ZEISS Co., Ltd.)₁、A₂、A₃、B₁、B₂、B₃In each cross section of the average thickness of the porous membrane at each position, an Inlens backscattered electron image is taken of any 2 fields of the central region (108a) of the first compartment (108) in which the porous membrane is formed. Next, the image is binarized by pattern method using image analysis software (for example: HALCON), and divided into a film portion and a void portion, and the ratio of the film portion to the void portion is calculated and is defined as A₁、A₂、A₃、B₁、B₂、B₃The porosity of the porous film at each position. The average value of the entire porous membrane was defined as the porosity of the porous membrane of the columnar honeycomb filter.

In order to achieve both high PN collection efficiency and low pressure loss, the porous membrane preferably satisfies the relational expression 0.36T + 60. ltoreq. P.ltoreq.0.75T +72 for the average membrane thickness T (unit:%) and the porosity P (unit:%), and more preferably satisfies the relational expression 0.42T + 67. ltoreq. P.ltoreq.0.75T +68 for the porous membrane, in addition to the average membrane thickness and porosity being controlled within the above ranges.

The material of the porous partition walls and the outer peripheral side walls of the columnar honeycomb filter according to the present embodiment is not limited, and porous ceramics may be used. Examples of the ceramics include: cordierite, mullite, zirconium phosphate, aluminum titanate, silicon carbide (SiC), silicon-silicon carbide composites (e.g., Si bonded SiC), cordierite-silicon carbide composites, zircon, zirconia, spinel, indialite, sapphirine, corundum, titania, silicon nitride, and the like. These ceramics may contain 1 kind alone or 2 or more kinds at the same time. In the case of filter applications such as DPF and GPF, cordierite can be preferably used as the ceramic. Therefore, the porous partition walls and the outer peripheral side wall preferably contain cordierite in an amount of 50 mass% or more, more preferably 70 mass% or more, and still more preferably 90 mass% or more.

The columnar honeycomb filter may carry a PM combustion catalyst that assists combustion of PM such as soot, an oxidation catalyst (DOC), an SCR catalyst and an NSR catalyst for removing nitrogen oxides (NOx), and a three-way catalyst that can simultaneously remove Hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx). However, the columnar honeycomb structure filter according to the present embodiment is preferably not loaded with a catalyst. This is because a pressure loss is increased.

The shape of the bottom surface of the columnar honeycomb filter is not limited, and examples thereof include circular arc shapes such as a circle, an ellipse, a racetrack shape, and an oblong shape, and polygons such as a triangle and a quadrangle. The bottom surface of the columnar honeycomb structure (100) of fig. 1 is circular and cylindrical as a whole.

The shape of the cell in a cross section perpendicular to the flow path direction of the cell is not limited, and is preferably a quadrangle, a hexagon, an octagon, or a combination of these shapes. Among them, square and hexagonal shapes are preferable. By forming the cell shape in the above-described shape, the pressure loss when the fluid flows through the columnar honeycomb structure can be reduced.

The average pore diameter of the partition walls is preferably 20 μm or less, more preferably 18 μm or less, and still more preferably 16 μm or less. When the average pore diameter of the partition walls is in the above range, the collection efficiency of the particulate matter is remarkably improved. The average pore diameter of the partition walls is preferably 4 μm or more, more preferably 6 μm or more, and still more preferably 8 μm or more. When the average pore diameter of the partition walls is in the above range, a decrease in pressure loss can be suppressed. The average pore diameter of the partition walls means: according to JIS-R1655: 2003 and measured by a mercury intrusion porosimeter.

From the viewpoint of suppressing the pressure loss of the exhaust gas to a low level, the porosity of the partition walls is preferably 40% or more, more preferably 45% or more, and still more preferably 50% or more. From the viewpoint of ensuring the strength of the columnar honeycomb structure filter, the porosity of the cell walls is preferably 80% or less, more preferably 75% or less, and still more preferably 70% or less. The porosity of the partition wall means: according to JIS-R1655: 2003 and measured by a mercury intrusion porosimeter.

From the viewpoint of suppressing the pressure loss, the upper limit of the average thickness of the partition walls in the columnar honeycomb structure filter is preferably 0.59mm or less, more preferably 0.33mm or less, and further preferably 0.26mm or less. However, from the viewpoint of ensuring the strength of the columnar honeycomb structure filter, the lower limit of the average thickness of the partition walls is preferably 0.15mm or more, more preferably 0.16mm or more, and still more preferably 0.18mm or more. In the present specification, the thickness of the partition wall means: when the centers of gravity of adjacent compartments are connected to each other by a line segment in a cross section perpendicular to the flow paths of the compartments, the line segment crosses the length of the partition wall. The average thickness of the partition walls means: the average of the thickness of all the partition walls.

The density of the cells (the number of cells per unit cross-sectional area perpendicular to the direction in which the cells extend) is not particularly limited, and may be, for example, 6 to 2000 cells/square inch (0.9 to 311 cells/cm)²) More preferably 50 to 1000 cells/square inch (7.8 to 155 cells/cm)²) Particularly preferably 100 to 400 cells/square inch (15.5 to 62.0 cells/cm)²)。

The columnar honeycomb filter may be provided in the form of an integrally molded article. In the case of the columnar honeycomb filter, a plurality of cells of the columnar honeycomb filter each having an outer peripheral side wall may be joined and integrated with each other at side surfaces, and may be provided in the form of a cell joint body. By providing the columnar honeycomb filter as a cell assembly, the thermal shock resistance can be improved.

< 2. method for manufacturing filter having columnar honeycomb structure

Hereinafter, a method for manufacturing a pillar-shaped honeycomb filter will be described as an example. First, a raw material composition containing a ceramic raw material, a dispersion medium, a pore-forming material, and a binder is kneaded to form a kneaded material, and then the kneaded material is extrusion-molded to form a desired columnar honeycomb molded body. Additives such as dispersants may be added to the raw material composition as needed. In the extrusion molding, a die having a desired overall shape, cell shape, partition wall thickness, cell density, and the like may be used.

After drying the columnar honeycomb formed body, plugging portions are formed at predetermined positions on both bottom surfaces of the columnar honeycomb formed body, and then the plugging portions are dried to obtain a columnar honeycomb formed body having plugging portions. Then, the columnar honeycomb formed body is degreased and fired to manufacture a columnar honeycomb structure.

As the ceramic raw material, a raw material capable of forming the above-described ceramic after firing can be used. The ceramic starting material may be provided in the form of, for example, a powder. Examples of the ceramic raw material include raw materials for obtaining ceramics such as cordierite, mullite, zirconium phosphate, aluminum titanate, silicon carbide (SiC), silicon-silicon carbide composite (for example, Si-bonded SiC), cordierite-silicon carbide composite, zircon, zirconia, spinel, indialite, sapphirine, corundum, titania, and silicon nitride. Specific examples include, but are not limited to: silica, talc, alumina, kaolin, serpentine, pyrophyllite, brucite, boehmite, mullite, magnesite, aluminum hydroxide, and the like. The ceramic raw materials may be used alone in 1 kind, or may be used in combination in 2 or more kinds.

In the case of filter applications such as DPF and GPF, cordierite can be preferably used as the ceramic. In this case, as the ceramic raw material, a cordierite forming raw material can be used. The cordierite forming raw material is a raw material which becomes cordierite by firing. Herba corydalis BungeanaeThe preferred chemical composition of the greening material is alumina (Al)₂O₃) (containing the aluminum hydroxide component converted to alumina): 30-45 mass%, magnesium oxide (MgO): 11 to 17 mass% and silicon dioxide (SiO)₂): 42 to 57% by mass.

Examples of the dispersion medium include water and a mixed solvent of water and an organic solvent such as alcohol, but water is particularly preferably used.

The pore-forming material is not particularly limited as long as it is a pore after firing, and examples thereof include: wheat flour, starch, foaming resin, water-absorbent resin, porous silica, carbon (such as graphite), ceramic floating beads, polyethylene, polystyrene, polypropylene, nylon, polyester, acrylic, phenolic, etc. The pore-forming material may be used alone in 1 kind, or may be used in combination in 2 or more kinds. From the viewpoint of improving the porosity of the fired body, the content of the pore former is preferably 0.5 parts by mass or more, more preferably 2 parts by mass or more, and still more preferably 3 parts by mass or more, per 100 parts by mass of the ceramic raw material. From the viewpoint of ensuring the strength of the fired body, the content of the pore-forming material is preferably 10 parts by mass or less, more preferably 7 parts by mass or less, and still more preferably 4 parts by mass or less, per 100 parts by mass of the ceramic raw material.

Examples of the binder include: and organic binders such as methyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, and polyvinyl alcohol. Particularly, it is preferable to use a combination of methylcellulose and hydroxypropylmethylcellulose. From the viewpoint of improving the strength of the honeycomb formed body, the content of the binder is preferably 4 parts by mass or more, more preferably 5 parts by mass or more, and still more preferably 6 parts by mass or more, per 100 parts by mass of the ceramic raw material. From the viewpoint of suppressing the occurrence of cracking due to abnormal heat generation in the firing step, the content of the binder is preferably 9 parts by mass or less, more preferably 8 parts by mass or less, and still more preferably 7 parts by mass or less, per 100 parts by mass of the ceramic raw material. The binder may be used alone in 1 kind, or may be used in combination in 2 or more kinds.

The dispersant may be ethylene glycol, dextrin, fatty acid soap, polyether polyol, etc. The dispersant may be used alone in 1 kind, or may be used in combination of 2 or more kinds. The content of the dispersant is preferably 0 to 2 parts by mass per 100 parts by mass of the ceramic raw material.

The method for sealing the bottom surface of the columnar honeycomb formed body is not particularly limited, and a known method can be used. The material of the plugging portion is not particularly limited, and is preferably ceramic from the viewpoint of strength and heat resistance. The ceramic is preferably a ceramic material containing at least 1 selected from the group consisting of cordierite, mullite, zircon, zirconium phosphate, aluminum titanate, silicon carbide, silicon nitride, zirconia, spinel, indian stone, sapphirine, corundum, and titania. Since the expansion rate at the time of firing can be made the same and the durability can be improved, the plugging portion is more preferably made of the same material composition as the partition walls of the honeycomb formed body.

The honeycomb formed body is dried, degreased, and fired, whereby a columnar honeycomb structure can be produced. The conditions of the drying step, the degreasing step, and the firing step may be known conditions depending on the material composition of the honeycomb formed body, and although not particularly described, specific examples of the conditions are given below.

In the drying step, for example, conventionally known drying methods such as hot air drying, microwave drying, dielectric drying, drying under reduced pressure, vacuum drying, and freeze drying can be used. Among these, a drying method combining hot air drying and microwave drying or dielectric drying is preferable in that the entire molded article can be dried quickly and uniformly.

In the case of forming the plugged portions, it is preferable to form the plugged portions on both bottom surfaces of the dried honeycomb formed body and then dry the plugged portions. The plugging portions are formed at predetermined positions so that a plurality of first cells extending from the inlet-side bottom surface to the outlet-side bottom surface and having the inlet-side bottom surface open and having the plugging portions on the outlet-side bottom surface, and a plurality of second cells extending from the inlet-side bottom surface to the outlet-side bottom surface and having the plugging portions on the inlet-side bottom surface and having the outlet-side bottom surface open are alternately arranged adjacent to each other with the porous partition walls interposed therebetween.

Next, the degreasing step will be explained. The combustion temperature of the adhesive is about 200 ℃, and the combustion temperature of the pore-forming material is about 300-1000 ℃. Therefore, the honeycomb formed body may be heated to a temperature of about 200 to 1000 ℃ and subjected to a degreasing step. The heating time is not particularly limited, and is usually about 10 to 100 hours. The honeycomb formed body after the degreasing step is referred to as a calcined body.

The firing step is also dependent on the material composition of the honeycomb formed body, and may be performed by heating the calcined body to 1350 to 1600 ℃ and holding it for 3 to 10 hours, for example. In this manner, a columnar honeycomb structure is produced, which includes: the first cells and the second cells are alternately arranged adjacent to each other with porous partition walls interposed therebetween.

Next, a porous film is formed on the surface of the first cell of the columnar honeycomb structure after the firing step. First, an aerosol containing ceramic particles is sprayed toward the inlet-side bottom surface, and an attractive force is applied to the outlet-side bottom surface, so that the sprayed aerosol is sucked from the inlet-side bottom surface, and the ceramic particles are attached to the surface of the first cell.

In this case, the ceramic particles in the aerosol preferably have a sharp and fine particle size distribution. Since the ceramic particles in the aerosol have a sharp and fine particle size distribution, the porous film obtained has a homogeneous three-dimensional structure having fine pores, and a high PN trapping efficiency can be easily obtained even when the film thickness is small. By making the film thickness thinner, low pressure loss can be achieved. Although it is difficult to accurately determine the homogeneous three-dimensional structure having fine pores, at least a part of the structure is represented in a low porosity form.

Specifically, the ceramic particles in the aerosol preferably satisfy the relational expressions of 0.1. ltoreq. D50. ltoreq.6.0 and 0.4. ltoreq. D50/(D90-D10) when the median particle diameter in the volume-based cumulative particle size distribution measured by the laser diffraction scattering method is D50 (unit: μm), the 10% particle diameter is D10 (unit: μm), and the 90% particle diameter is D90 (unit: μm).

The upper limit of D50 in the ceramic particles is preferably 6.0 μm or less, more preferably 4.0 μm or less, and still more preferably 3.0 μm or less. The lower limit of D50 in the ceramic particles is not particularly limited, but is usually 0.1 μm or more, preferably 0.5 μm or more, and more preferably 1.0 μm or more, from the viewpoint of ease of production.

The sharp particle size distribution can be represented by D50/(D90-D10). The degree of aggregation of the ceramic particles can be particularly shown by using D50/(D90-D10) as an index. D50/(D50-D10) as defined in patent document 1 does not exhibit a sharp particle size distribution. A larger D50/(D90-D10) means a sharp particle size distribution. Specifically, it is preferably 0.4. ltoreq. D50/(D90-D10), more preferably 0.6. ltoreq. D50/(D90-D10), still more preferably 0.8. ltoreq. D50/(D90-D10), still more preferably 1.0. ltoreq. D50/(D90-D10), and for example, it may be 0.4. ltoreq. D50/(D90-D10). ltoreq.1.5.

As the ceramic particles, the ceramic particles constituting the porous film are used. Specifically, it may contain a material selected from the group consisting of silicon carbide (SiC), cordierite, talc, mica, mullite, ceramic particles, aluminum titanate, alumina, silicon nitride, sialon, zirconium phosphate, zirconium oxide, titanium oxide, and silicon dioxide (SiO)₂) One or more than two kinds of ceramics. Among them, the ceramic particles preferably contain one or two or more selected from silicon carbide, cordierite, alumina, silica, mullite, and aluminum titanate in a total amount of 50 mass% or more, more preferably 70 mass% or more, and still more preferably 90 mass% or more, for reasons of cost, availability, thermal shock resistance, and peeling resistance. The ceramic particles contain silicon carbide in an amount of particularly preferably 50 mass% or more, more preferably 70 mass% or more, and still more preferably 90 mass% or more, for reasons of thermal shock resistance and peeling resistance.

Fig. 5 schematically shows an apparatus configuration of a particle attaching apparatus (500) suitable for performing a step of attaching ceramic particles to the surface of the first cell of the columnar honeycomb structure (580). A particle attachment device (500) is provided with: an aerosol generator (510), a laser diffraction particle size distribution measuring device (520), a gas introduction pipe (530), a holder (540), a differential pressure gauge (550), an exhaust pipe (560), and a blower (570).

An aerosol generator (510) is provided with:

a cylinder (513) for storing ceramic particles (512);

a piston or screw (514) for sending out the ceramic particles (512) stored in the cylinder (513) from a cylinder outlet (513 e);

a crushing chamber (515) which communicates with the cylinder outlet (513e) and is provided with a rotating body (516) for crushing the ceramic particles (512) sent out from the cylinder outlet (513 e); and

and a gas flow path (517) through which the dielectric gas flows, which communicates with the crushing chamber outlet (515e) in the middle, and which can eject an aerosol containing the dielectric gas and the ceramic particles (512) from a nozzle (511) attached to the tip thereof.

The aerosol generator (510) can eject aerosol from the nozzle (511). Ceramic particles (512) having been adjusted to a predetermined particle size distribution are accommodated in a cylinder (513). The ceramic particles (512) contained in the cylinder (513) are extruded from a cylinder outlet (513e) by a piston or a screw (514). In this case, the extrusion speed can be adjusted. Ceramic particles (512) discharged from a cylinder outlet (513e) enter a crushing chamber (515). The ceramic particles (512) introduced into the crushing chamber (515) are crushed by the rotating body (516), move in the crushing chamber (515), and are discharged from the crushing chamber outlet (515 e). As the rotating body 516, for example, a rotating brush can be used. The rotating body (516) may be driven by a motor, and may be configured so that the rotation speed thereof can be controlled.

The ceramic particles discharged from the crushing chamber outlet (515e) are mixed with the medium gas flowing through the gas passage (517) to form an air aerosol, and the air aerosol is ejected from the nozzle (511). The nozzle (511) is preferably provided at a position and in a direction perpendicular to the inlet-side bottom surface, so as to spray the aerosol toward the center of the inlet-side bottom surface of the columnar honeycomb structure (580) held by the holder (540).

The medium gas uses a compressed gas such as compressed air whose pressure has been adjusted, whereby the ejection flow rate from the nozzle (511) can be controlled. A laser diffraction particle size distribution measuring device (520) is provided in the gas flow path (517), and the particle size distribution of ceramic particles in the aerosol discharged from the aerosol generator (510) can be measured in real time. This makes it possible to monitor whether or not ceramic particles having a desired particle size distribution are being supplied to the columnar honeycomb structure (580).

The fine ceramic particles have a property of being easily aggregated. However, since the crushed ceramic particles are ejected using the aerosol generator (510) according to the present embodiment, the ceramic particles having the target particle size distribution in which the agglomeration is suppressed can be attached to the surface of the first compartment.

The aerosol ejected from the aerosol generator (510) passes through the gas introduction pipe (530) by the suction force from the blower (570), and is then sucked into the first compartment of the columnar honeycomb filter from the inlet-side bottom surface of the columnar honeycomb held by the holder (540). The ceramic particles in the aerosol drawn into the first compartment adhere to the surface of the first compartment.

A plurality of vent holes (531) are provided in the wall surface of the gas introduction pipe (530), and ambient gas such as air can be sucked in. Thus, the flow rate of the gas flowing into the gas introduction pipe (530) can be adjusted according to the suction force from the blower (570). For the reason of preventing the foreign matter from being mixed, a filter may be provided in the vent hole (531).

An exhaust pipe (560) connected to a blower (570) is provided downstream of the outlet-side bottom surface of the columnar honeycomb structure (580). Therefore, if the ceramic particle-removed aerosol is discharged from the outlet-side bottom surface of the columnar honeycomb structure (580), the aerosol passes through the exhaust pipe (560) and is discharged by the blower (570).

When the step of adhering the ceramic particles to the surfaces of the first cells is continued, the pressure loss between the inlet-side bottom surface and the outlet-side bottom surface of the columnar honeycomb structure increases as the amount of adhering ceramic particles increases. By obtaining the relationship between the amount of adhesion of the ceramic particles and the pressure loss in advance, the end point of the step of adhering the ceramic particles to the surface of the first cell can be determined based on the pressure loss. Therefore, the particle adhesion device (500) can be provided with a differential pressure gauge (550) to measure the pressure loss between the inlet-side bottom surface and the outlet-side bottom surface of the columnar honeycomb structure (580), and the end point of the process can be determined based on the value of the differential pressure gauge.

When the step of adhering ceramic particles to the surfaces of the first cells is performed, the ceramic particles adhere to the inlet-side bottom surface of the columnar honeycomb structure (580), and therefore it is preferable to remove the ceramic particles by suction such as vacuum while flattening the inlet-side bottom surface with a tool such as a doctor blade.

Then, the columnar honeycomb structure having the ceramic particles adhered to the surface of the first cell is subjected to a heating treatment under a condition of being held at a maximum temperature of 1000 ℃ or more for 1 hour or more, typically at a maximum temperature of 1100 ℃ to 1400 ℃ for 1 hour to 6 hours, thereby completing the columnar honeycomb structure filter. The heating treatment can be performed by placing the columnar honeycomb structure in, for example, a continuous firing furnace (for example, a tunnel kiln) or a batch firing furnace (for example, a shuttle kiln). For the reason of increasing the production rate, it is preferable that the average rate of temperature rise from room temperature (25 ℃) to the maximum temperature in the heating treatment is 100 ℃/Hr or more. For the reason of suppressing the occurrence of cracking, it is preferable that the average temperature increase rate from room temperature (25 ℃) to the maximum temperature during temperature increase in the heating treatment is 200 ℃/Hr or less. Further, for the reason of suppressing the occurrence of cracking and reducing the burden on the kiln charge, it is preferable that the average temperature reduction rate from the highest temperature to room temperature (25 ℃) in the temperature reduction in the heating treatment is 200 ℃/Hr or less. The ceramic particles are bonded to each other by the heat treatment, and the ceramic particles are sintered to the partition walls in the first compartment, thereby forming a porous film on the surface of the first compartment. When the heat treatment is performed under an oxygen-containing condition such as air, a surface oxide film is formed on the surfaces of the ceramic particles to promote adhesion of the ceramic particles to each other. Thus, a porous film that is not easily peeled off was obtained.

The average film thickness T (unit: μm) of the porous film formed on the surface of the first compartment by the heat treatment preferably satisfies a relation of 4 XD 50. ltoreq.T.ltoreq.20 XD 50 with D50 (unit: μm) of the ceramic particles. The relationship states: when D50 is small, the average film thickness T is preferably small, and when D50 is large, the average film thickness T is preferably large. The reason is that: the smaller the D50, the smaller the exhaust gas flow path of the porous membrane, and the higher the collection efficiency.

Examples

Hereinafter, examples for better understanding of the present invention and advantages thereof will be described by way of illustration, but the present invention is not limited to the examples.

(1) Manufacture of cylindrical honeycomb filters

To 100 parts by mass of a cordierite forming raw material, 3 parts by mass of a pore-forming material, 55 parts by mass of a dispersion medium, 6 parts by mass of an organic binder, and 1 part by mass of a dispersant were added, and the mixture was mixed and kneaded to prepare a clay. As the cordierite forming raw material, alumina, aluminum hydroxide, kaolin, talc, and silica are used. Water was used as the dispersion medium, a water-absorbent polymer was used as the pore-forming material, hydroxypropylmethylcellulose was used as the organic binder, and a fatty acid soap was used as the dispersant.

This clay was put into an extrusion molding machine and extrusion-molded through a die having a predetermined shape to obtain a cylindrical honeycomb molded body. The obtained honeycomb molded body was subjected to dielectric drying and hot air drying, and then both bottom surfaces were cut into a predetermined size to obtain a honeycomb dried body.

The obtained honeycomb dried body was sealed with cordierite as a material so that the first cells and the second cells were alternately arranged adjacent to each other, and then heated and degreased at about 200 ℃ in an atmospheric atmosphere, and further fired at 1420 ℃ for 5 hours in an atmospheric atmosphere to obtain a columnar honeycomb structure.

The specification of the columnar honeycomb structure is as follows.

The overall shape is as follows: cylindrical shape with diameter of 132mm x height of 120mm

Cell shape in cross section perpendicular to flow path direction of cell: square shape

Cell density (number of cells per unit cross-sectional area): 200cpsi

Average pore diameter: 9 μm

Porosity: 55 percent of

Thickness of the partition wall: 8mil (200 μm) (nominal value based on die specification)

With respect to the columnar honeycomb structure produced as described above, ceramic particles were attached to the surfaces of the first cells using a particle attaching apparatus having a configuration shown in fig. 5. The operating conditions of the particle adhesion device are as follows.

Aerosol generator: RBG2000 manufactured by PALAS

Ceramic particles housed in the cylinder: table 1 shows (in the table, "main material" means that 90% by mass or more of the material is constituted by the indicated substances.)

(the particle size distribution of the ceramic particles stored in the cylinder was changed according to the test number.)

The medium gas: drying air

Ambient gas: atmosphere (es)

Mean flow rate of the aerosol flowing inside the columnar honeycomb structure: 3000L/Min

Laser diffraction particle size distribution measurement apparatus: incitec Spray manufactured by MALVERN Inc

During the operation of the particle adhesion apparatus, the particle size distribution of the ceramic particles discharged from the aerosol was measured by a laser diffraction particle size distribution measuring apparatus, and D50 and D50/(D90-D10) were measured. The results are shown in Table 1. From this result, it was confirmed that: in both examples and comparative examples, the particle size distribution of the ceramic particles contained in the cylinder was substantially the same, and no aggregation occurred.

The inlet-side bottom surface of the thus obtained columnar honeycomb structure to which the ceramic particles are attached is flattened by a doctor blade, and the ceramic particles attached to the inlet-side bottom surface are removed by suction under vacuum. Then, the columnar honeycomb structure was placed in a batch electric furnace, and heat treatment was performed under an atmospheric atmosphere under conditions of holding at a maximum temperature of 1200 ℃ for 2 hours, whereby a porous film was formed on the surface of the first cell, and a columnar honeycomb structure filter was obtained. In the heat oxidation treatment, in each test example, the average temperature increase rate from room temperature (25 ℃) to the maximum temperature at the time of temperature increase was set to 100 ℃/Hr, and the average temperature decrease rate from the maximum temperature to the room temperature (25 ℃) at the time of temperature decrease was set to 100 ℃/Hr. The number of the columnar honeycomb filters required for the performance evaluation described below was determined.

(2) Evaluation of characteristics

[ film weight ]

The weight of the porous membrane of each of the columnar honeycomb filters obtained by the above-described production methods was determined. Specifically, the weight of the columnar honeycomb structure before the ceramic particles are attached to the columnar honeycomb structure is subtracted from the weight of the columnar honeycomb structure filter to obtain a value, which is the membrane weight. The results are shown in Table 1.

[ average film thickness ]

The average thickness of the porous film of each of the columnar honeycomb filters obtained by the above-described production methods was measured by the above-described method. The 3D shape measuring apparatus used for the measurement was VR-3200 manufactured by Keyence. The results are shown in Table 1.

[ porosity of film ]

The porosity of the porous film was measured by the method described above. The apparatus used for the measurement was FE-SEM (model: ULTRA55 (manufactured by ZEISS Co., Ltd.)) and image analysis software HALCON. The results are shown in Table 1. An FE-SEM photograph of the porous membrane in example 2 is exemplarily shown in fig. 8. The gray portion is a film portion, and the black portion is a void portion.

The "collection efficiency (%)" and the "pressure loss" of each of the columnar honeycomb filters obtained by the above-described production methods were measured by the following procedure.

[ Capture efficiency (%) ]

The columnar honeycomb filter was connected to the outlet side of the engine exhaust manifold of a 1.2L direct injection gasoline engine vehicle, and the number of soot contained in the gas discharged from the outlet port of the columnar honeycomb filter was measured by a PN measurement method. As the running mode, a running mode (RTS95) simulating the worst case of the RDE running is implemented. The accumulation of the number of the soot discharged after the mode traveling is set as the number of the soot of the exhaust gas purification device to be determined, and the collection efficiency (%) is calculated from the number of the soot. The results are shown in Table 1.

[ pressure loss ]

Exhaust gas discharged from a 1.2L direct injection gasoline engine was heated at 700 ℃ to 600m³The flow rate of the flow was measured, and the pressures on the inlet side and the outlet side of the columnar honeycomb structure filter were measured. Then, the pressure difference between the inlet side and the outlet side was calculated, and the pressure loss (kPa) of the honeycomb filter was obtained. The results are shown in Table 1.

TABLE 1

(3) Investigation of

Fig. 6 shows the relationship between the average film thickness and the porosity of the porous films in examples and comparative examples. Fig. 7 shows the relationship between the median particle diameter (D50) of the ceramic particles in the aerosols and the average film thickness of the porous film in the examples and comparative examples. As can be seen from table 1 and fig. 6: the porous film having the average film thickness T and the porosity P satisfying the predetermined conditions can achieve both high PN trapping efficiency and low pressure loss. In addition, as can be seen from table 1 and fig. 7: when D50, D50/(D90-D10), and the average film thickness T satisfy predetermined conditions, a porous film capable of achieving both high PN trapping efficiency and low pressure loss is obtained.