JPH1181983A - Particulate filter - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To reduce the pressure loss and to excel in the particulate collection efficiency, and to increase the collected particulates even when the exhaust gas temperature is low, such as when starting the engine. To provide a particulate filter capable of performing flameless combustion with the filter. SOLUTION: Particulates in exhaust gas are collected,
In the particulate filter for burning and removing, the average surface roughness Rz of the base material of the particulate filter was set to 30 to 1000 μm. Further, a plurality of trap chambers 34 and communication holes 36 connecting the trap chambers 34 are provided inside the base material 32. Further, the base material 62,
The heat insulating layers 66 and 76 are provided on at least a part of the surface of the substrate 72, for example, on the concave portion of the surface of the substrate 62, the inner wall surface of the trap chamber 64, or the gas outlet side portion of the substrate 72.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a particulate filter, and more particularly, to a particulate filter which collects particulate matter contained in exhaust gas discharged from a diesel engine or an automobile engine in an exhaust system and burns and removes the particulate matter. It relates to a curated filter.

[0002]

2. Description of the Related Art Exhaust gas emitted from diesel engines and automobile engines contains particulates (fine particles) composed of soot, hydrocarbons, sulfates, metal oxides and the like adsorbed on the soot. I have. The particulates are particularly contained in the exhaust gas of the diesel engine, and it is said that the particulates are mainly generated by decomposition or incomplete combustion in a high-temperature region where air is low.

[0003] In order to collect such particulates in an exhaust gas exhaust system, various particulate filters have already been proposed. These can be roughly classified into ceramic materials and metal materials based on the material, and the ceramic materials are classified into honeycomb filters, foam filters, fiber filters, and the like according to their shapes.

In particular, since honeycomb filters made of ceramics materials such as cordierite and silicon carbide have excellent heat resistance and thermal shock resistance, particulates for diesel engines and automobile engines used under severe conditions are used. It is attracting attention as a filter.

[0005] The honeycomb filter is obtained by extruding a ceramic material into a honeycomb shape and cutting it into a predetermined length. A large number of cells are formed in a base material constituting a main part of the honeycomb filter, and the cells are separated from each other by thin partition walls. further,
Honeycomb filters are classified into a straight flow type in which both ends of a cell are opened, and a wall flow type in which a cell inlet and a cell outlet are alternately plugged.

FIG. 10 is a sectional view showing a state in which a honeycomb filter 10 of a straight flow type is disposed in an exhaust gas passage 18. In this state, Particulate 1
When the exhaust gas containing 6, 16, ... flows, the particulates 16, 16, ... are part of the base material 12 while the exhaust gas flows through the cells 14, 14, ... formed in the base material 12. Contact with the surface of the partition walls 12a, 12a.

FIG. 11 is a cross-sectional view showing a state in which a wall-flow type honeycomb filter 20 is disposed in the exhaust gas passage 18. For wall flow type,
Since the base material 22 is made of a porous material, in this state, when the exhaust gas containing the particulates 16, 16,... Flows, the exhaust gas is separated from the partition walls 22a, 22a,.
, And at that time, the particulates 16, 16 are collected on the surface of the partition walls 22a, 22a... And the pores inside the partition walls 22a, 22a.

In the case of a wall flow type honeycomb filter, the collection efficiency and pressure loss depend on the pore diameter of the substrate. That is, if the pore diameter of the base material is too small, the trapping efficiency of the particulates increases, but the pressure loss when the exhaust gas passes through the partition walls increases. Conversely, if the pore diameter is too large, the pressure loss will be small, but the particulate collection efficiency will decrease. Therefore, usually, an appropriate pore diameter or pore diameter distribution is selected.

Various methods are known for controlling the pore size and pore size distribution of the base material of the honeycomb filter. For example, Japanese Patent Application Laid-Open No. Hei 5-23512 discloses that α-type silicon carbide powder having an average particle size of 11 μm has an average particle size of 0.3 μm.
A technique of obtaining a diesel particulate filter having a pore diameter of 1 to 15 μm and a deviation value of a pore diameter distribution of 0.20 or less by adding β-type silicon carbide powder and firing under predetermined conditions. I have.

Japanese Patent Application Laid-Open No. 5-139861 discloses that β-type silicon carbide having an average particle size of 0.1 μm is mixed with a powder having a larger particle size of 0.5 to 100 μm (for example, α-type silicon carbide). By mixing and firing at a predetermined temperature,
A technique for obtaining a porous silicon carbide sintered body having a pore diameter of 60 μm is disclosed.

Further, it is necessary to remove the particulates collected by the particulate filter at a stage where a certain amount is collected, and to regenerate the particulate filter. Since most of the collected particulates are combustibles such as soot, the particulate filter is usually regenerated by burning and removing the particulates.

As a means for regenerating the particulate filter, specifically, a method of burning and removing a particulate collected by the particulate filter by an electric heater or a burner while blowing air with a blower while the engine is stopped is known. (See JP-A-7-133713).

Further, the pore size and pore size distribution of the particulate filter are appropriately controlled to increase the contact area between the particulate and the base material, and when the exhaust gas temperature of the engine reaches a certain value or more, the base material There is also known a method of burning and removing particulates collected at a relatively low temperature without flame using oxygen remaining in exhaust gas.

[0014]

However, in the former method, there is a problem that the ignition and burning temperatures of the particulates increase, and the base material of the particulate filter composed of cordierite or the like is damaged or broken. is there. For this reason, at present, this method has not been adopted widely for particulate filters for automobiles.

On the other hand, the latter method has an advantage in that the deposited particulates are burned and removed at a relatively low temperature, so that the base material is not melted or cracked. However, when the exhaust gas temperature of the engine is low, such as at the time of starting the engine, at a low speed, and at a low load, there is a disadvantage that particulate combustion is not performed.

Therefore, for example, when a straight-flow type honeycomb filter is used as a particulate filter, the particulates generated at the time of starting the engine and the like thickly accumulate on the inner wall surface of the cell, and the cell is closed to increase the pressure loss. There is a problem that the particulates that cannot be collected and collected are discharged out of the engine as they are.

Further, for example, when a wall flow type honeycomb filter is used as a particulate filter, if the pore size of the substrate is too small, the particulates are deposited in a layer on the surface of the substrate and the substrate is clogged. And the pressure loss increases. If the pore diameter is increased to avoid this, the trapping efficiency of the particulates decreases. In addition, there is a problem in that the contact area between the particulates and the base material is reduced, so that the combustion efficiency is reduced and it becomes difficult to purify the particulates. Therefore, the conventional method of simply controlling the pore diameter or the like cannot obtain a filter having sufficient performance.

The problem to be solved by the present invention is that the pressure loss is small and the particulate collection efficiency is excellent.
In addition, it is an object of the present invention to provide a particulate filter capable of causing the collected particulates to be flamelessly burned with high efficiency even when the temperature of the exhaust gas is low, such as when the engine is started.

[0019]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention relates to a particulate filter for collecting and burning off particulates in exhaust gas.
The gist is that the average surface roughness Rz of the base material constituting the particulate filter is 30 to 1000 μm.

When the average surface roughness Rz of the base material constituting the particulate filter is set to 30 to 1000 μm and predetermined irregularities are formed on the base material surface, when exhaust gas flows through the particulate filter, the exhaust gas flows near the base material surface. The flow of the exhaust gas is disturbed, and the frequency of contact between the particulates and the substrate increases. Therefore, the collection efficiency of particulates improves as compared with the case where the surface of the base material is a smooth surface.

In addition, the increase in the contact area between the particulates and the surface of the base material makes it easier for the particulates to burn and lowers the ignition temperature of the particulates. Therefore, even when the temperature of the exhaust gas is low, such as when starting the engine, the particulate combustion proceeds and the exhaust gas is purified.

Further, the particulate filter includes:
It is desirable that the base material have a plurality of trap chambers and a communication hole connecting the trap chambers. When a plurality of trap chambers and a communication hole connecting the trap chambers are provided inside the base material, when exhaust gas passes through the particulate filter,
The particulates contained in the exhaust gas are conveyed from one trap chamber to the next via a communication hole.

At this time, the particulates not collected on the surface of the base material are sequentially collected in a trap chamber formed inside the base material, so that the amount of the particulates that escape to the outlet side of the particulate filter is extremely small. Become. Further, since the surface area for collecting particulates becomes large, an increase in pressure loss due to clogging of the base material does not easily occur. Further, since the contact area between the particulates and the base material increases, the ignition temperature of the particulates also decreases, and the combustion efficiency improves.

Further, the particulate filter is
It is preferable that a heat insulating layer is provided on at least a part of the surface of the base material. When a heat insulating layer is provided on a part of the surface of the base material, the dissipation of heat generated by the burning of the particulates is prevented, so that the ignition temperature of the particulates is further reduced and the combustion efficiency is improved.

Here, it is effective that the heat insulating layer is provided so that a portion serving as a combustion reaction field of the particulates is insulated. Specifically, it is preferable to provide a heat insulating layer in a concave portion of the substrate surface having a predetermined average surface roughness Rz. Further, the inner wall surface of the trap chamber formed inside the substrate also corresponds to the “substrate surface”, and a heat insulating layer can be provided. In particular, in the case of a wall flow type honeycomb filter, a heat insulating layer having a porosity higher than that of the gas inflow side portion may be provided in the gas outflow side portion of the substrate.

An oxide catalyst, a noble metal, or the like is formed on the surface of the base material of the particulate filter having the above-described structure, the inner wall surface of the trap chamber formed inside the base material, or the surface of the heat insulating layer formed on the base material surface. When a catalyst or the like is carried, the ignition temperature of the particulates can be further reduced. In addition to the oxide catalyst and the noble metal catalyst, if a NOx reducing catalyst, a NOx storage material, a thermal property control material, etc. are supported, not only can the particulate combustion efficiency be improved, but also the NOx reduction can be achieved. It becomes possible.

Specifically, the oxide catalyst may be CeO
₂, Fe₂O₃, Pr₂O₃, Pr ₆O₁₁Single phase
Alternatively, multiple phases can be used. Also, with precious metal catalysts
Of platinum, palladium, rhodium, iridium, etc.
Single or multiple phases can be used. In addition, single phase
Alternatively, a multi-phase oxide catalyst and a single-phase or multi-phase precious metal
A composite catalyst with a metal catalyst may be used.

[0028]

Embodiments of the present invention will be described below in detail. In the particulate filter according to the present invention, the average surface roughness Rz of the substrate is 30 to 1000 μm.
Is limited to the following reasons.

That is, the average surface roughness Rz of the substrate is 30
If it is less than μm, for example, in the case of a honeycomb filter of a straight flow type, the collection efficiency of particulates is reduced. If the average surface roughness Rz is too small, when the exhaust gas passes near the partition walls of cells formed inside the substrate,
This is because the turbulence of the flow of the exhaust gas is reduced, and the frequency of contact between the particulates and the base material is reduced.

In the case of a wall flow type honeycomb filter, if the average surface roughness Rz of the substrate is too small, most of the particulates are trapped on the partition wall surface when exhaust gas passes through the partition wall, and This is because the curate is densely deposited in a layer on the partition wall surface.

On the other hand, the average surface roughness Rz of the substrate is 1
If it exceeds 000 μm, for example, in the case of a honeycomb filter of a straight flow type, there is a problem that the pressure loss increases due to a decrease in the cell opening area. Further, for example, in the case of a honeycomb filter of a wall flow type, it becomes difficult to form irregularities on the substrate surface without increasing the pressure loss.

For the above reasons, the average surface roughness Rz of the substrate
Should be 30 to 1000 μm. In the case of a straight-flow type honeycomb filter, as the average surface roughness Rz increases, the particulate collection efficiency and the combustion efficiency tend to increase. However, when the average surface roughness Rz is too small, the trapping efficiency is sharply reduced and the ignition temperature is increased. On the other hand, the average surface roughness R
If z is too large, the pressure loss will increase. Considering these points, in order to obtain a straight flow type particulate filter having a high collection efficiency and a high combustion efficiency and a small pressure loss, the average surface roughness Rz of the base material must be 1
A range of 70 to 700 μm is particularly preferred.

The material of the base material constituting the particulate filter and the shape of the filter are not particularly limited. For example, various materials such as a ceramic material such as cordierite, silicon carbide, silicon nitride, and mullite and a metal material can be used for the base material. Further, the shape of the base material may be any of a honeycomb filter, a foam filter, and a fiber filter. Further, a catalyst may be supported on the surface of the base material.

Further, when the substrate has a honeycomb shape of a straight flow type, the substrate may be made of either a dense material or a porous material. When the substrate is formed into a wall flow type honeycomb shape, there is no particular limitation except that the average surface roughness Rz is within the above range, and the porosity, the average pore diameter, and the pore diameter distribution of the substrate. Can be appropriately selected according to the environment in which the filter is used.

Next, the process of collecting and burning particulates by a particulate filter having a predetermined surface roughness on the surface of the substrate will be described. When a particulate filter having a predetermined average surface roughness Rz is disposed in the exhaust gas flow path, and the exhaust gas containing particulates flows in the exhaust gas flow path, for example, in the case of a straight flow type particulate filter, the exhaust gas Flows through the inside of the cell partitioned by. In the case of a particulate filter of the wall flow type, the exhaust gas passes through the inside of the partition wall from the gas inflow side to the gas outflow side.

At this time, the average surface roughness Rz of the substrate is 30 to
When the unevenness corresponding to the surface roughness is formed on the surface of the substrate at 1000 μm, the flow of the exhaust gas when the exhaust gas passes near the partition wall surface which is a part of the substrate or when the exhaust gas passes through the partition wall And the frequency of contact between the particulates contained in the exhaust gas and the surface of the substrate increases. Therefore, the collection efficiency of particulates on the substrate surface is improved as compared with the case where the substrate surface is a smooth surface.

Further, the increase in the contact area between the particulate and the surface of the base material facilitates the burning of the particulate and lowers the ignition temperature of the particulate. Therefore, even when the temperature of the exhaust gas is low, such as when starting the engine, the exhaust gas can be purified. further,
As the burning of particulates progresses from the low temperature range, the cells are less likely to be clogged and the substrate is less likely to be clogged,
An increase in pressure loss is suppressed.

Next, the average surface roughness Rz of the substrate is 30 to 1
A method for manufacturing a particulate filter having a size of 000 μm will be described. There are various methods for producing the particulate filter having the average surface roughness Rz within the above range. When a ceramic material is used as the base material, for example, a method of adding a coarse pore former to the raw material powder,
Alternatively, a method of applying a slurry containing a coarse pore-forming material to the surface of the base material is preferable.

The production of a particulate filter by a method of adding a coarse pore former to the raw material powder (hereinafter referred to as "method A") is specifically performed according to the following procedure. That is, first, to a ceramic raw material powder such as cordierite and silicon carbide, a flammable coarse pore former made of graphite particles having a predetermined particle size, carbon black, resin particles, etc. and a binder are added, and these are uniformly mixed. Knead. Next, the kneaded raw material is formed into a predetermined shape, and the obtained molded body is fired at a predetermined temperature.

A part of the coarse pore-forming material added to the raw material powder is uniformly dispersed inside the molded body, and the other part is exposed on the surface of the molded body. Therefore, when the obtained molded body is fired at a predetermined temperature, the coarse pore forming material is burned and gasified and volatilized, and pores are formed inside the base material,
A desired average surface roughness Rz is given to the substrate surface.

In the case of manufacturing a honeycomb filter, the kneaded raw material is extruded into a honeycomb shape and then extruded.
What is necessary is just to cut to predetermined length. Further, the firing is generally a calcining step of burning and removing the coarse pore former and degreasing,
It comprises a sintering step for sintering ceramics. The firing temperature can be appropriately selected in consideration of the combustion characteristics of the coarse pore former, the sintering characteristics of the ceramic raw material, and the like.

Further, the average surface roughness Rz of the base material is determined by the particle size of the coarse pore former added to the raw material powder, the compounding ratio, and the sintering shrinkage of the ceramic. Generally, the larger the particle size and the mixing ratio of the coarse pore former, the larger the average surface roughness Rz.
Therefore, the particle size and the mixing ratio of the coarse pore former may be selected so as to obtain a desired average surface roughness Rz in consideration of the contraction rate of the ceramic.

The production of a particulate filter by a method of applying a slurry containing a coarse pore-forming material to the surface of a substrate (hereinafter referred to as "method B") is specifically performed according to the following procedure. That is, first, a base material constituting a main part of the filter is prepared in advance. The material and shape of the substrate are not particularly limited.

For example, in the case of a straight flow type honeycomb filter, the substrate may be made of a dense material, or may be made of a porous material. Further, for example, in the case of a honeycomb filter of a wall flow type, a base material having an average pore diameter, a porosity, and the like according to a use is prepared. Furthermore, the substrate may be a sintered body that has undergone a sintering step, or may be a calcined body that has undergone only a calcination step.

Next, a raw material powder (for example, powder having the same composition as the substrate) having good bondability with the substrate is provided with flammable coarse pores made of graphite particles having a predetermined particle size, carbon black, or the like. The material and the binder are added to form a slurry. The above-described substrate is immersed in the obtained slurry, and the surface of the substrate is coated with the slurry.

Further, after drying the coating layer formed on the surface of the substrate, it is fired at a predetermined temperature. As a result, the raw material powder contained in the slurry applied to the surface of the substrate and the substrate are sintered and integrated, and the coarse pore-forming material contained in the slurry is burned and gasified and volatilized. A desired average surface roughness Rz is imparted to the surface.

According to the above-mentioned method A, the pores are formed inside the base material and the desired average surface roughness Rz is given to the base material surface by one baking step. It is suitable as a method for producing a particulate filter of a type. Further, when the method A and the method B are used together, there is an advantage that the average pore diameter inside the substrate and the average surface roughness Rz of the substrate surface can be independently controlled.

When the substrate is made of a material containing glass, the substrate obtained as described above may be placed in an autoclave and treated with high-temperature and high-pressure steam. The autoclave treatment softens or melts the vitreous surface, so that the average surface roughness Rz of the substrate can be further increased.

Next, the structure of a particulate filter having a plurality of trap chambers in a base material and a communication hole connecting the trap chambers will be described with reference to the drawings. FIG.
It is an enlarged sectional view of such a particulate filter. In the particulate filter 30, a large number of trap chambers 34, 34,...
Each of the trap chambers is connected by a plurality of communication holes 36.

Here, the size of the trap chambers 34, 34,... Is desirably 30 to 300 μm. If the size of the trap chambers 34, 34 is less than 30 μm, the trapping efficiency and the burning efficiency of the particulates in the trap chambers 34, 34 decrease. If the size of the trap chambers 34, 34... Exceeds 300 μm, the frequency of contact between the particulates and the trap chambers 34, 34. Further, if the size of the trap chambers 34, 34,... Becomes excessively large, it becomes difficult to manufacture the particulate filter 30 structurally.

The diameter of the communication holes 36, 36,.
It is desirable to be in the range of 00 μm. Communication holes 36, 3
If the diameter of 6 is less than 5 μm, the communication holes 36 are undesirably clogged and the pressure loss increases. When the diameter of the communication holes 36, 36 ... exceeds 100 μm,
It is not preferable because the trapping efficiency and the burning efficiency of the particulates in the trap chambers 34, 34 ... decrease.

When the diameter of the communication holes 36 is equal to or greater than the size of the trap chambers 34, 34, the communication holes 36 become equal to a structure in which the three-dimensionally connected pores are uniformly dispersed. Various effects obtained by providing 36, 36... Cannot be obtained. Therefore, the communication holes 36, 3
Of course, it is necessary to make the diameter of 6 ... smaller than the size of the trap chambers 34, 34 ....

The material and shape of the substrate 32 are not particularly limited, and various materials and shapes can be used as in the case of the above-described particulate filter having a rough substrate surface. It is. Above all, cordierite is particularly suitable as the material of the base material because the formation of the communication hole is easy. The wall flow type honeycomb filter is particularly suitable as the shape of the base material because various effects obtained by providing the trap chamber and the communication hole inside the base material are remarkable.

Next, the process of collecting and burning particulates by the particulate filter having the trap chamber and the communication hole shown in FIG. 3 will be described. When a particulate filter 30 having a plurality of trap chambers 34, 34, and communication holes 36, 36 ... connecting the trap chambers 34, 34 ... is disposed in the exhaust gas flow path, and when the exhaust gas containing the particulates flows, Part of the exhaust gas enters the trap chamber 34 opened on the surface of the substrate 32.

When exhaust gas enters the trap chamber 34,
Part of the particulates contained in the exhaust gas is collected on the inner wall surface of the trap chamber 34. After the remaining particulates stay in the trap chamber 34 for a while, they are sequentially conveyed through the communication holes 36 into the trap chambers 34, 34. At this time, the substrate 3
Since the particulates not collected on the two surfaces are sequentially collected on the inner wall surfaces of the trap chambers 34, 34,... While being conveyed, the amount of particulates that escape to the outlet side of the particulate filter is extremely small.

Since the trap chambers 34, 34,... Are provided with a large surface area for trapping particulates, the particulates do not accumulate thickly on the surface of the base material 32 or the inner wall surface of the trap chamber 34. Moreover, since each of the trap chambers 34, 34,... Is connected by the plurality of communication holes 36, 36,. It is conveyed to the next trap chamber 34 via. As a result, the particulate filter 30 is less likely to be clogged, and an increase in pressure loss is suppressed.

Since the diameters of the communication holes 36 are smaller than the diameters of the trap chambers 34, the particulates pass through the communication holes 36 at a high speed and are discharged to the next trap chamber 34. Then, the flow rate of the particulates decreases, and the particulates stay there for a while. Therefore, as compared with the conventional filter in which the pores are uniformly dispersed, the frequency at which the particulates collide with the inner wall surface of the trap chamber 34 before the exhaust gas passes through the particulate filter increases. As a result, the ignition temperature of the particulates decreases, and the combustion efficiency of the particulates improves.

Next, a method of manufacturing a particulate filter having a trap chamber and a communication hole will be described. The trap chamber and the communication hole can be formed by various methods according to the material of the base material. In particular, when cordierite is used as a base material, there is an advantage that communication holes can be formed inside cordierite particles at the stage of synthesizing cordierite. Methods for forming the communication holes at the stage of synthesizing cordierite include a method using coarse talc and a method using granulated powder.

The production of a particulate filter by a method using coarse talc (hereinafter referred to as “method C”) is specifically performed according to the following procedure. That is, first, alumina, kaolin, and talc are prepared as starting materials. In this case, the particle size of talc is coarser than that of alumina and kaolin.

Next, alumina, kaolin and talc powders are weighed and mixed at a ratio of 15, 40 and 45 wt%, respectively, and mixed. Further, a predetermined amount of a combustible coarse pore-forming material (for example, low-temperature combustible material such as carbon black particles or resin particles having an average particle diameter of about 200 μm), a molding binder and water are added to the mixed powder and mixed. I do. The compounding ratio is
It can be appropriately selected according to the molding method. When performing extrusion molding, the compounding ratio is, for example, 49 wt% of the mixed powder.
%, Coarse pore former 20wt%, molding binder 13wt
% And 18 wt% of water.

FIG. 4A schematically shows a cross-sectional view of the obtained molded body. Inside the molded body 40, coarse pore-forming materials 42 are dispersed. Also, since the ratio of talc is high, a three-dimensional network structure of coarse talc particles 44, 44,... Is formed around the coarse pore-forming materials 42, 42,. Further, the coarse pores 42, 4
2 and the talc particles 44 are filled with a fine mixed powder 46 of alumina and kaolin.

Next, the compact having a cross-sectional structure as shown in FIG. 4A is dried and degreased, and is further subjected to a heat treatment (calcination) in the air to remove the coarse pore-forming material. At this stage, as shown in FIG.
Are burned out, and coarse pores 42a, 42a,... Are formed later.

In the next firing step, the calcined substrate is heated to about 1400 ° C. to synthesize cordierite. At this time, when the temperature of the base material becomes about 1300 ° C. or higher, the talc 44 melts as shown in FIG.
This melt is mixed powder 4 of the surrounding alumina and kaolin.
The place where talc was sucked by 6 was
4a, 44a... Thereby, the coarse air holes 42a,
A three-dimensional network of pores 44a, 44a,... Connecting between 42a, that is, communicating holes is formed. Then, in the final stage of firing, the mixture of alumina and kaolin and the molten talc react to form cordierite.

The size of the trap chamber can be controlled by adjusting the particle diameter of the coarse pore material added to the raw material powder. The larger the coarse pore material, the larger the trap chamber. Can be formed. Similarly, the size of the communication hole can be controlled by adjusting the particle size of talc used for synthesizing cordierite, and the smaller the particle size of talc, the smaller the diameter of the communication hole.

However, if the particle size of talc is too small, the diameter of the communication hole formed in cordierite becomes too small, which is not preferable. Further, it is not preferable because pores generated by melting talc may be isolated without communicating. On the other hand, if the particle size of talc is too large, the size of the communication hole becomes equal to or larger than the size of the trap chamber, and it is not preferable because various effects by providing the communication hole cannot be obtained. Therefore, the particle size of the talc used in the method C is preferably 5 to 200 μm.

The production of a particulate filter by a method using granulated powder (hereinafter referred to as “method D”) is specifically performed according to the following procedure. That is, first, alumina, kaolin, and talc are prepared as starting materials. In this case, the particle size of talc is 10 to 30.
μm. In the case of the method D, unlike the method C, the talc does not necessarily have to be coarser than the alumina and the kaolin.

Next, the alumina and kaolin powders were
Mix at a ratio of 15:45, average particle size of 40 to 100 μm
To produce granulated powder. Note that a slight amount of talc may be added to the granulated powder.

Separately, predetermined amounts of the above-mentioned alumina, kaolin and talc are weighed and mixed. The mixing ratio of the mixed powder, when this mixed powder is added to the granulated powder,
Alumina: kaolin: talc ratio is 15: 4 in total
0:45. Therefore, since talc is hardly contained in the granulated powder, the ratio of talc in the mixed powder naturally increases.

Next, a predetermined amount of granulated powder, mixed powder, flammable coarse pore forming material (for example, low-temperature combustible material such as carbon black particles and resin particles having an average particle diameter of about 200 μm), a molding binder and water are added. It is weighed and mixed, and a molded body is prepared by extrusion molding or the like. Note that a fine pore former, fine kaolin, fine talc, or the like may be mixed with these mixtures.

FIG. 5 (a) schematically shows a cross-sectional view of the obtained molded body. Inside the molded body 50, coarse pore-forming materials 52 are dispersed. Also, since the ratio of the granulated powders 54, 54... Made of alumina and kaolin is high, the granulated powders 5 around the coarse pores 42, 42.
, A three-dimensional network structure is formed. Further, coarse pore-forming materials 52, 52,.
The gap 54 is filled with a mixed powder 56 of alumina, kaolin and talc.

Next, the compact having a cross-sectional structure as shown in FIG. 5A is dried and degreased, and further subjected to a heat treatment (calcination) in the air to remove a coarse pore-forming material. At this stage, as shown in FIG.
Are burned off, and coarse pores 52a, 52a,... Are formed later. Further, fine pores (not shown) are generated inside the granulated powders 54, 54.

Further, in the next firing step, the calcined substrate is heated to about 1400 ° C. to synthesize cordierite. At this time, when the temperature of the base material becomes about 1300 ° C. or more, as shown in FIG. 5C, a large amount of talc contained in the mixed powder 56 is melted, and the melt is removed from the surrounding alumina and kaolin. Are absorbed by the granulated powder 54, 54 ...
The places where the talc existed are the pores 56a, 56a. As a result, a three-dimensional network of pores 56a, 56a... Connecting the coarse atmospheric pores 52a, 52a, that is, communication holes is formed. And in the final stage of firing,
The mixture of alumina and kaolin and the molten talc react to form cordierite.

As described above, according to the method C or the method D, there is an advantage that a plurality of communication holes connecting the trap chambers can be easily formed at the stage of synthesizing cordierite. Further, there is an advantage that the diameter of the communication hole can be easily controlled by controlling the particle diameter of the cordierite to be used, the particle diameter of the granulated powder, and the like. In addition, since a large pore material is used to form the trap chamber,
At the same time trap chamber during firing is formed, becomes rough average surface roughness Rz of the substrate, high particulate filters capture efficiency and combustion efficiency. Further, Method C
Alternatively, when the methods D and B are used in combination, the average surface roughness Rz of the substrate can be further increased.

The method of forming the communication hole is not limited to the above method C or D, but may be formed by using another method. For example, the particle size of the ceramic raw material powder, which is the main component of the base material, is adjusted, pores formed at the triple point of each particle of the ceramic raw material powder are connected to form communication holes, and the trap chambers are connected using the communication holes. You may. In addition, by appropriately adjusting the particle size and the amount of carbon black and graphite particles added as a pore-forming material, the trap chamber generated by burning the coarse pore-forming material is connected to the trap chamber formed by burning the fine pore-forming material. It may be connected by a hole.

Next, the structure of a particulate filter having a heat insulating layer provided on at least a part of the surface of a substrate will be described with reference to the drawings. FIG. 7 is an enlarged sectional view of such a particulate filter. The particulate filter 60 has a large number of trap chambers 6 in a base material 62.
4, 64... Further, the trap chambers 64, 64
Are open at the surface of the base material 62,
2 has a predetermined surface roughness. Further, a heat insulating layer 66 is formed on the surface of the base material 62 and the inner wall surfaces of the trap chambers 64, 64.

Here, it is necessary that the heat insulating layer 66 be made of a substance having a heat conductivity and a heat capacity smaller than the heat conductivity and the heat capacity of the substrate 62. Specifically, for example, when cordierite is used as the base material 62, the thermal insulation layer 66 may be made of titania (TiO ₂ ) or silica (Si
O ₂ ) is preferred.

The heat insulating layer 66 formed on the surface of the base material 62
Is preferably 1 μm or more and 50 μm or less. If the thickness of the heat insulating layer 66 is less than 1 μm, heat insulation becomes insufficient, and the ignition temperature of particulates cannot be lowered, which is not preferable. The thickness of the heat insulating layer 66 is 50 μm.
Is exceeded, the average surface roughness Rz of the surface of the substrate 62 is reduced, or the trap chambers 66 and 66 formed inside the substrate 62 are reduced.
Are undesirably reduced in size, resulting in reduced combustion efficiency and increased pressure loss.

The material and shape of the base material 62 are not particularly limited, and various materials and shapes can be used, unlike the above-described particulate filter having a rough surface. The same is true. Further, the base material 62
The invention is not limited to only those having the trap chambers 64, 64. For example, in the case of a honeycomb filter of a straight flow type, a honeycomb structure made of a dense material provided with a predetermined average surface roughness Rz by the method B may be used as the substrate 62.

Next, the configuration of a particulate filter according to another embodiment in which a heat insulating layer is provided on a part of the surface of the substrate will be described. In particular, in the case of a particulate filter of a wall flow type, since the exhaust gas passes through a partition which is a part of the base material, the gas outflow side portion of the partition has a higher porosity than the gas inflow side portion. A heat insulating layer may be provided. FIG. 8 shows an example of this, in which the particulate filter 70 has a large number of trap chambers 7 inside a base material 72.
4, 74... Are formed. Further, a heat insulating layer 76 is formed on the gas outlet side portion of the base material 72.

Here, the heat insulating layer 7 provided on the gas outflow side portion
The porosity of No. 6 is desirably 60% or more. If the porosity of the heat insulating layer 76 is less than 60%, the heat insulation of the base material 72 becomes insufficient, and the ignition temperature of particulates cannot be lowered, which is not preferable. The higher the porosity of the heat insulating layer 76 is, the better it can be manufactured.

The heat insulating layer 76 provided on the gas outflow side portion
Is preferably 20 to 500 μm. If the thickness of the heat insulating layer 76 is less than 20 μm, the heat insulation of the base material 72 becomes insufficient, and the ignition temperature of the particulates cannot be lowered, which is not preferable. The thickness of the heat insulating layer 76 is 5
If it exceeds 00 μm, the pressure loss increases, which is not preferable.

Next, the collecting process and the burning process of the particulate by the particulate filter having the heat insulating layer shown in FIGS. 7 and 8 will be described. As shown in FIGS. 7 and 8, the particulate filters 60, 70 provided with a heat insulating layer on a part of the surfaces of the base materials 62, 72 are disposed in the exhaust gas flow path, and when the exhaust gas containing the particulates flows, the exhaust gas Are recesses on the surfaces of the substrates 62 and 72 or the substrates 62 and 7
2 enter trap chambers 64 and 74 formed therein.
And the particulates in the exhaust gas are
It is collected on two surfaces or the inner wall surfaces of the trap chambers 64 and 74.

Here, in order to burn the particulates contained in the exhaust gas flamelessly with the oxygen remaining in the exhaust gas, it is necessary to bring the particulates and the oxygen into sufficient contact with each other, and the particulates are deposited. Base material 6
It is necessary to heat the surfaces of 2, 72 and the inside of the trap chambers 64, 74 to a temperature required for ignition of particulates.

However, in an ordinary filter having no heat-insulating layer, even if the particulates deposited on or in the base materials 62 and 72 burn first, the heat of combustion reaction passes through the base materials 62 and 72. When the exhaust gas temperature is low, the particulate combustion does not proceed continuously. Therefore, in order to continuously burn the particulates deposited on the surfaces of the substrates 62 and 72 or the trap chambers 64 and 74, it is necessary to wait for the exhaust gas temperature to rise, and the burning temperature of the particulates becomes high as a whole system. Become.

On the other hand, as shown in FIG. 7, a heat insulating layer 66 is provided on the surface of the substrate 62 and the inner wall surface of the trap chamber 64, which serve as a combustion reaction field for particulates, or as shown in FIG. In the case where the heat insulating layer 76 is provided on the gas outlet side portion 72, the combustion reaction heat of the initially burned particulates is accumulated in the substrates 62 and 72, and the accumulated combustion reaction heat is deposited thereon. It will be used to ignite the next particulate. As a result, even when the exhaust gas temperature is low, the burning of the particulates proceeds continuously, and the burning temperature of the particulates in the entire system decreases.

Next, a method of manufacturing a particulate filter having a heat insulating layer on at least a part of the surface of a substrate will be described. As a method for providing a heat insulating layer on the substrate surface and inside the trap chamber, for example, there is a method of immersing the entire substrate in a heat insulating slurry (hereinafter, referred to as “method E”).

The production of the particulate filter by the method E is specifically performed according to the following procedure. That is, first, the base material of the particulate filter is manufactured. The substrate may be a substrate having a predetermined average surface roughness Rz obtained by the method A or B, or a substrate having a trap chamber and a communication hole obtained by the method C or D. Further, a substrate obtained by combining methods A to D may be used.

Next, the whole obtained substrate is immersed in an aqueous solution in which a slurry, sol or metal salt of a heat insulating material such as titania (TiO ₂ ) or silica (SiO ₂ ) is dissolved, dried, and then dried at a predetermined temperature. Heat treatment. Thereby, a heat insulating layer is formed on the surface of the base material and the inner wall surface of the trap chamber.

Here, for forming the heat insulating layer, it is desirable to use a slurry of a ceramic powder, a colloid solution, an alkoxide, an aqueous solution of a metal salt, or the like. When a solid powder made of a heat insulating material is formed into a slurry and the substrate is immersed in the slurry to form a heat insulating layer, the particle size of the powder needs to be smaller than the pore diameter of the substrate. Specifically, a powder having an average particle size of 5 μm or less is suitable. Further, the thickness of the heat insulating layer can be controlled by adjusting the slurry concentration, the number of times of immersion, and the like.

Further, a heat insulating layer having a porosity higher than the porosity of the gas inflow side portion (hereinafter referred to as “the heat outflow layer”) is provided on the gas outflow side portion of the substrate.
As a method of providing a “high porosity heat insulating layer”, for example, a method of forming a high porosity heat insulating layer by selectively applying slurry only to the gas outlet side portion of the substrate (hereinafter, “method F”) There is).

The production of the particulate filter by the method F is specifically performed according to the following procedure. That is, first, a wall flow type substrate is prepared. In this case, for example, a substrate in which pores having substantially the same size are uniformly dispersed may be used, but a wall flow type honeycomb filter having a trap chamber and a communication hole obtained by the method C or the method D may be used. It is desirable to use

Next, a pore-forming material having a finer grain size than the coarse pore-forming material used for preparing the base material and a ceramic material constituting the high-porosity heat-insulating layer were made into a slurry state, and only the gas-outflow-side portion of the base material was formed. Apply slurry. In the case of a wall flow type honeycomb filter, since the cells are plugged alternately, the slurry can be easily applied only to the inner wall surface of the cell on the gas outflow side. Furthermore, if the applied slurry is dried and degreased and then fired at a predetermined temperature, a high porosity heat insulating layer is formed on the gas outflow side.

The porosity of the high-porosity heat-insulating layer can be controlled by the particle size and the mixing ratio of the pore former added to the slurry, the slurry concentration, and the like. Further, the thickness of the high porosity heat insulating layer can be controlled by the slurry concentration, the number of times of immersion, and the like.

(Example 1) A wall flow type particulate filter having a predetermined average surface roughness Rz was produced by using the method A. That is, as a starting material, alumina having an average particle size of 1.2 μm and an average particle size of 1.0 μm were used.
m kaolin and talc with an average particle size of 10 μm,
Alumina was weighed to be 15 wt%, kaolin was to be 40 wt%, and talc was to be 45 wt%, and these were mixed (hereinafter, this is referred to as “cordierite composition powder A”).

Next, the cordierite composition powder A was 64 wt.
36% by weight of graphite particles having an average particle diameter of 30 to 300 μm as a pore former, 10% by weight of a binder (trade name “Selander”) and 30% by weight of water were externally added thereto. Next, this compound was kneaded and formed into a honeycomb-shaped formed body having a diameter of 35 mm and a length of 50 mm by extrusion molding. After degreased the obtained molded body, it was fired under the condition of 1440 ° C. × 2 hours in the air atmosphere, and thereafter, the cell inlet and the cell outlet were alternately plugged to obtain a wall flow type particulate filter. Was.

When the surface roughness of the base material of the obtained particulate filter was measured by a non-contact surface roughness meter, the average surface roughness Rz was 170 μm. When the pore diameter of the substrate was measured with a mercury porosimeter, the average pore diameter was 50 μm.

(Comparative Example 1) As a pore former, a particle size of 5 to 50 was used.
A wall flow type particulate filter was manufactured in the same procedure as in Example 1 except that graphite particles of μm were used. When the average surface roughness Rz and the average pore diameter of the obtained particulate filter were measured by the same procedure as in Example 1, the average surface roughness Rz was 20 μm.
m, and the average pore diameter was 15 μm.

A combustion test was performed on the particulate filters obtained in Example 1 and Comparative Example 1 in order to examine the relationship between the average surface roughness Rz of the substrate and the burning characteristics (burning efficiency) of the particulates. . The combustion test was performed according to the following procedure. That is, the exhaust gas generated by the combustion of light oil (diesel oil) was caused to flow from the cell inlet side of the particulate filter, and soot was previously collected on the cell inner wall surface of the base material.

Next, an inlet gas temperature detector is provided on the cell inlet side of the particulate filter, and CO and CO ₂ concentration detectors are provided on the cell outlet side, respectively. N ₂ , O ₂ and NO ₂ are provided from the cell inlet side. Was introduced while increasing the temperature, and the relationship between the incoming gas temperature (° C.) and the amount of CO + CO ₂ (ppm) generated by combustion of the soot was measured. The results are shown in FIG. In addition, in the case of FIG. 1, the catalyst is not carried on the base material surface in any of the particulate filters.

In Comparative Example 1 in which the average surface roughness Rz of the substrate was 20 μm (smooth surface), the amount of CO + CO ₂ in the exhaust gas discharged from the particulate filter gradually increased when the temperature of the incoming gas exceeded 400 ° C. Began to increase. Also, if the incoming gas temperature exceeds 500 ° C., CO + CO ₂
The amount increased sharply and peaked at an incoming gas temperature of 650 ° C. At this time, the amount of CO + CO ₂ is 52 ppm.
Met.

On the other hand, the average surface roughness Rz of the substrate was 1
In Example 1 having a thickness of 70 μm (rough surface), CO in the exhaust gas
The amount of + CO ₂ started to increase gradually from a relatively low temperature where the incoming gas temperature was about 300 ° C. Also, CO + in exhaust gas
The amount of CO ₂ showed a higher value than Comparative Example 1 when the temperature of the incoming gas was in the range of 300 ° C. to 550 ° C. Further, when the inlet gas temperature exceeded 550 ° C., on the contrary, the amount of CO + CO ₂ became smaller than that in Comparative Example 1, and the inlet gas temperature at which the amount of CO + CO ₂ reached the peak value decreased to 620 ° C. In addition, the amount of CO + CO ₂ at this time also dropped to 36 ppm.

From the above results, when the surface of the base material of the particulate filter is roughened, the soot combustion efficiency in the low temperature range (300 ° C. to 500 ° C.) is improved as compared with the case where the surface is smooth. all right. In addition, since combustion of the collected soot proceeds even in a low temperature range, CO + CO ₂
It was found that the temperature at which the amount reached the peak value shifted to the lower temperature side, and the peak value also decreased.

(Example 2) A wall flow type particulate filter having a predetermined average surface roughness Rz was manufactured by using the method B. That is, cordierite (2MgO.2) was prepared according to the same procedure as in Example 1 except that graphite particles having a particle size of 5 to 100 μm were used as the pore former.
A wall flow type honeycomb sintered body made of Al ₂ O ₃ .5SiO ₂ ) was produced.

Next, in order to roughen the surface of the substrate, 35 wt% of cordierite powder having an average particle diameter of 1.2 μm, 10 wt% of a polyvinyl alcohol-based binder, and 3
A slurry comprising 30 wt% of 0 to 300 μm graphite particles, 0.5 wt% of an ammonium polycarboxylate dispersant, and the balance water was prepared.

Next, the above-mentioned honeycomb sintered body was immersed in the slurry, and the slurry was attached to the surface of the substrate.
After drying and degreasing, 1
By baking at 410 ° C. × 1 hour, a wall flow type particulate filter was obtained.

When the surface roughness of the obtained particulate filter was measured by a non-contact surface roughness meter, the average surface roughness Rz was 170 μm. In addition, when a combustion test was performed in the same procedure as in Example 1, as in Example 1, a higher amount of CO + CO ₂ than in Comparative Example 1 was detected in a low-temperature region where the inlet gas temperature was 300 ° C. to 500 ° C. Further, as compared with Comparative Example 1 described above, it was confirmed that the temperature at which the amount of CO + CO ₂ reached the peak value shifted to a lower temperature side, and the peak value also decreased.

Example 3 Ceria (Ce) was used as an oxidation catalyst.
A particulate filter supporting O ₂ ) was produced by the following procedure. That is, a wall flow type particulate filter was manufactured according to the same procedure as in Example 1. Next, the obtained particulate filter was immersed in an aqueous solution of cerium nitrate for 30 minutes, and then heat-treated at 500 ° C. × 2 hours under an air atmosphere. When the surface roughness of the substrate after supporting the catalyst was measured by a non-contact surface roughness meter, the average surface roughness Rz
Was 170 μm.

The obtained particulate filter was subjected to a combustion test in the same procedure as in Example 1, and CO + CO ₂ in the exhaust gas at an inlet gas temperature of 400 ° C.
The amount (ppm) was measured. The results are shown in FIG. FIG. 2 also shows the results of the particulate filters obtained in Example 1 and Comparative Example 1.

The amount (ppm) of CO + CO ₂ in the exhaust gas at an inlet gas temperature of 400 ° C. was the lowest in Comparative Example 1 in which the substrate surface was smooth, and was only 3 ppm. On the other hand, in Example 1 in which the substrate surface was rough, 8 ppm was used.
Example 3 in which a catalyst was supported on the substrate surface
Increased to 20 ppm. From the above results, it was found that when the surface of the base material was roughened and the catalyst was supported on the surface of the base material, the burning efficiency of particulates in the low temperature range was further improved.

(Example 4) A straight flow type particulate filter having a predetermined average surface roughness Rz was produced by using the method B. That is, first, 10 wt% of a binder (trade name “Serander”) was added to the cordierite composition powder A used in Example 1 by external addition.
And 30 wt% of water. In the case of the straight flow type, since it was not necessary to control the pore diameter of the substrate, no pore former was added.

Next, this mixture was kneaded and extruded to obtain a honeycomb-shaped formed body having a diameter of 35 mm and a length of 50 mm. The obtained molded body was degreased and further fired under the condition of 1440 ° C. × 2 hours in an air atmosphere to obtain a honeycomb sintered body.

Next, in order to increase the surface roughness of the substrate,
35 wt% cordierite composition powder A, particle size 10-50
30% by weight of μm graphite particles and 10% by weight of binder
%, 0.5 wt% of ammonium polycarboxylate dispersant
%, And the balance was made up of water. The above-mentioned honeycomb sintered body was immersed in this slurry, and the slurry was attached to the surface of the honeycomb sintered body. Then, after drying, baking was performed under the condition of 1410 ° C. × 1 hour in an air atmosphere to obtain a straight flow type particulate filter. When the surface roughness of the obtained particulate filter was measured with a non-contact surface roughness meter, the average surface roughness Rz was 30 μm.

Example 5 A straight flow type particulate filter was manufactured in the same procedure as in Example 4 except that the particle size of the graphite particles added to the slurry was 30 to 300 μm. When the surface roughness of the obtained particulate filter was measured with a non-contact surface roughness meter, the average surface roughness Rz was 170 μm.

(Example 6) A straight flow type particulate filter was produced in the same procedure as in Example 4, except that the particle size of the graphite particles added to the slurry was 100 to 800 µm. When the surface roughness of the obtained particulate filter was measured with a non-contact surface roughness meter, the average surface roughness Rz was 550 μm.

Example 7 A straight flow type particulate filter was manufactured in the same procedure as in Example 4 except that the particle size of the graphite particles added to the slurry was 300 to 900 μm. When the surface roughness of the obtained particulate filter was measured with a non-contact surface roughness meter, the average surface roughness Rz was 700 μm.

Example 8 Example 4 was repeated except that the particle size of the graphite particles added to the slurry was 500 to 1100 μm.
According to the same procedure as described above, a straight flow type particulate filter was produced. When the surface roughness of the obtained particulate filter was measured with a non-contact surface roughness meter, the average surface roughness Rz was 1000 μm.

(Comparative Example 2) [0117] A slurry containing graphite particles was applied to the surface of a base material, and sintering was not performed.
In accordance with the same procedure as in Example 4, a straight flow type particulate filter was produced. When the surface roughness of the obtained particulate filter was measured with a non-contact surface roughness meter, the average surface roughness Rz was 20 μm.

Comparative Example 3 Example 4 was repeated except that the particle size of the graphite particles added to the slurry was 700 to 1200 μm.
According to the same procedure as described above, a straight flow type particulate filter was produced. When the surface roughness of the obtained particulate filter was measured with a non-contact surface roughness meter, the average surface roughness Rz was 1100 μm.

For each of the particulate filters obtained in Examples 4 to 8 and Comparative Examples 2 to 3, soot collection efficiency (%), CO + CO ₂ amount (ppm) at an inlet gas temperature of 400 ° C., soot combustion peak Temperature (° C.) and pressure loss (mmH ₂ O) were measured.

The soot collection efficiency was represented by the ratio (%) of the amount of soot discharged from the filter to the amount of soot that had flowed into the filter. The soot emission was measured using a smoke meter attached to the downstream side of the filter, with the soot generated by burning light oil flowing from the upstream side of the filter while the surface temperature of the filter was maintained at about 200 ° C. .

The pressure loss was represented by the pressure difference (mmH ₂ O) between the inlet side and the outlet side of the filter. The pressure difference is 1.5 kg / mm of room temperature air from the inlet side of the filter.
^2. Flow was performed at a flow rate of 2 l / min, and the measurement was performed using a differential pressure gauge attached to the inlet side and the outlet side of the filter. further,
CO + CO ₂ amount (ppm) and combustion peak temperature (° C)
Was measured by the same procedure as in Example 1. Table 1 shows the results
Shown in

[0122]

[Table 1]

In Comparative Example 2 in which the average surface roughness Rz was 20 μm, the soot collection efficiency was 40%. In contrast,
Examples 4 and 170 μm in which the average surface roughness was 30 μm
In Example 5, the soot collection efficiency was 55%, respectively.
And 65%. Further, the average surface roughness Rz is 55
In Examples 6 to 8 where the thickness was 0 to 1000 μm, the soot collection efficiency was improved to 70%, and the average surface roughness Rz was 110%.
In Comparative Example 3 in which 0 μm was set, the soot collection efficiency reached 72%.

In Comparative Example 2 in which the average surface roughness Rz was 20 μm, CO + C
Almost no O ₂ was detected, and the amount of CO + CO ₂ at an inlet gas temperature of 400 ° C. was 3 ppm. On the other hand, when the average surface roughness Rz was set to 30 μm or more, CO + CO ₂ was detected, albeit a little, in a low temperature region of the incoming gas. Further, CO at an incoming gas temperature of 400 ° C
The amount of + CO ₂ was 8 ppm in Example 4 and 10 p in Example 5.
pm and increased to 13 ppm in Examples 6 to 8 and Comparative Example 3.

The combustion peak temperature (° C.) of the soot was highest in Comparative Example 2 in which the average surface roughness Rz was 20 μm.
50 ° C was indicated. In Example 4 in which the average surface roughness Rz was 30 μm, the temperature was 630 ° C., and further the average surface roughness Rz was
In each of Examples 5 to 8 and Comparative Example 3 in which the temperature was 170 μm or more, the temperature was lowered to 620 ° C.

Further, the pressure loss was only 1 mmH ₂ O in Comparative Example 1 in which the average surface roughness Rz was 20 μm. Example 4 where the average surface roughness Rz was 30 μm
In Examples 5 and was 170 [mu] m, the pressure loss are each 2mmH ₂ O and 3mmH ₂ O, there was no significant change in the pressure loss.

The average surface roughness Rz is 550 μm (Example
6), 700 μm (Example 7) and 1000 μm (actual
Example 8) As the pressure increases, the pressure loss increases by 10
mmH ₂O, 20mmH₂O and 30mmH₂Increase to O
However, at this level of pressure loss, engine performance
There was no effect. However, the average surface roughness Rz is 1
In Comparative Example 3 having 100 μm, the pressure loss was 50 mmH.
₂O, and the engine performance decreased. This is the cell
This is because the passage area of the gas flowing through the inside is reduced.

From the above results, the average surface roughness Rz was 30
When it is less than μm, it was found that the pressure loss was small but the combustion characteristics of soot decreased. Further, the average surface roughness Rz is 100
When it exceeds 0 μm, it has been found that the combustion characteristics of soot are good, but the pressure loss increases. That is, the average surface roughness Rz of the substrate from which a soot combustion characteristic was good and a straight flow type particulate filter having a small pressure loss was obtained was in the range of 30 μm to 1000 μm. Also, from Table 1, the average surface roughness Rz is 170 to
It turns out that the range of 700 μm is particularly suitable.

Further, ceria was supported as an oxide catalyst on each of the particulate filters obtained in Examples 4 to 8 and Comparative Examples 2 to 3 according to the same procedure as in Example 3. For each of the obtained particulate filters, the average surface roughness Rz (μm), soot collection efficiency (%), CO
The amount of + CO ₂ (ppm), the combustion peak temperature of soot (° C.), and the pressure loss (mmH ₂ O) were measured. Table 2 shows the results.

[0130]

[Table 2]

From Table 2, it can be seen that by supporting the catalyst,
Although there is no effect on soot collection efficiency and pressure loss, it can be seen that soot combustion efficiency is improved. That is, when the average surface roughness Rz is 550 μm or more, the incoming gas temperature 400
The amount of CO + CO _{2 at} 0 ° C. increased to 30 ppm, and the combustion peak temperature of the soot decreased to 500 ° C. this is,
This is because the rougher the surface roughness of the filter, the larger the contact area between the soot and the catalyst, and the greater the effect of the catalyst.

(Example 9) A wall flow type particulate filter having a trap chamber and a communication hole was produced by using the method C. That is, as a starting material, alumina having an average particle size of 1.2 μm and an average particle size of 1.0 μm were used.
m kaolin and talc with an average particle size of 40 μm,
Alumina was weighed to be 15 wt%, kaolin was to be 40 wt%, and talc was to be 45 wt%, and these were mixed (hereinafter, this will be referred to as “cordierite composition powder B”).

Next, the cordierite composition powder B was 64 wt.
%, 36% of graphite particles having an average particle diameter of 200 μm as a pore-forming material.
wt%, this 10 wt% binder (trade name "Seranda") outside the addition, and water was 30 wt% blended and kneaded, 35mm diameter by extrusion molding, the cross-sectional area 6.25 mm ² of the honeycomb, length 50mm Was obtained. Next, this molded body was degreased and fired at 1440 ° C. for 2 hours under an atmospheric pressure atmosphere. Further, the cell inlet and the cell outlet were plugged alternately to obtain a wall flow type particulate filter.

As shown in FIG. 3, a number of trap chambers 34, 34... Having an average diameter of 180 μm generated by the combustion of graphite particles are formed inside the base material of the obtained particulate filter. Are not only three-dimensionally connected to each other, but also mutually connected by a plurality of communication holes 36, 36 having an average diameter of 20 μm formed by melting coarse talc. Had been linked.

Comparative Example 4 A wall flow type particulate filter was produced in the same procedure as in Example 9 except that talc having an average particle size of 1.4 μm was used. A large number of trap chambers 34, 34... Having an average diameter of 180 μm generated by the combustion of graphite particles were formed inside the base material of the obtained particulate filter, but communication holes were formed inside the base material 32 made of cordierite. 36, 36
Are not formed, and only the trap chambers 34 are connected three-dimensionally.

A combustion test was performed on the particulate filters obtained in Example 9 and Comparative Example 4. The test conditions were the same as in Example 1. FIG. 6 shows the results.

In Comparative Example 4 having no communication hole, CO + CO in the exhaust gas discharged from the particulate filter was used.
_{The two} quantities started to increase gradually when the incoming gas temperature exceeded 400 ° C. Further, when the inlet gas temperature exceeds 500 ° C., the amount of CO + CO ₂ rapidly increases, and the inlet gas temperature becomes 620 ° C.
The peak value was reached at ℃. Also, CO + CO at this time
_The amount was 110 ppm.

On the other hand, in the ninth embodiment in which each trap chamber is connected by a communication hole, the amount of CO + CO ₂ in the exhaust gas is
The incoming gas temperature began to increase sharply from a relatively low temperature of about 350 ° C. In addition, the amount of CO + CO ₂ in the exhaust gas is the same as in Comparative Example 4 when the incoming gas temperature is in the range of 300 ° C. to 550 ° C.
It showed higher values. Furthermore, the incoming gas temperature is 550 ° C
On the contrary, the amount of CO + CO ₂ was smaller than that of Comparative Example 4, and the gas temperature at which the amount of CO + CO ₂ reached the peak value was lowered to 520 ° C. CO + CO ₂ at this time
The amount also dropped to 68 ppm.

Further, with respect to the particulate filters obtained in Example 9 and Comparative Example 4, soot collection efficiency and pressure loss were measured in the same procedure as in Example 4. As a result, the soot collection efficiency was 95% in Example 9 in which the communication holes were provided, and was 98% in Comparative Example 4 in which the communication holes were not provided. Although the collection efficiency was slightly reduced by providing the communication holes, this difference is a value that does not cause a problem in practical use. Moreover, pressure loss, while the a 30mmH ₂ O Example 9, the pressure loss was found to be 1/2 by mmH ₂ O next in Comparative Example 4, the communicating hole provided.

From the above results, when the trap chamber is connected by a plurality of communication holes, the combustion efficiency of soot can be increased without lowering the efficiency of trapping soot, and the particulates having less pressure loss can be obtained. It turned out that a filter was obtained.

(Example 10) By using the method E, a wall flow type particulate filter having a heat insulating layer on the surface of the base material and the inner wall surface of the trap chamber was manufactured. That is, according to the same procedure as in Example 1, a honeycomb sintered body of a wall flow type was manufactured. Next, the obtained honeycomb sintered body was immersed in a titania (TiO ₂ , average particle size: 0.2 μm) slurry having a concentration of 65 wt%, dried at 80 ° C. for 2 hours, and fired at 800 ° C. for 1 hour in an air atmosphere. As a result, a wall flow type particulate filter was obtained.

The obtained particulate filter (hereinafter referred to as “heat insulating material coated filter”) had an average pore diameter of 50 μm and a porosity of 60%. Further, the surface of the base material 62 made of cordierite and the trap chambers 64, 64.
As shown in FIG. 7, a 1.0 μm thick Ti
The heat insulating layer 66 made of O ₂ was formed.

(Example 11) A wall flow type particulate filter having a high porosity heat-insulating layer on the gas outflow side portion of a substrate was manufactured by using the method F. That is, using the same raw material as in Example 1, a honeycomb formed body was produced by extrusion molding, the formed body was degreased, then calcined, and the cell inlet and cell outlet were plugged alternately to obtain a honeycomb calcined body. Obtained.

Next, the cordierite composition powder A used in Example 1 was 35 wt%, the graphite particles having a particle size of 5 to 20 μm were 30 wt%, the binder was 10 wt%, the ammonium polycarboxylate dispersant was 0.5 wt%, A slurry having a balance of water was prepared, and the above-described honeycomb calcined body was immersed in the slurry, and the slurry was attached only to the gas outflow side portion of the honeycomb calcined body. After drying this, it is further baked under the condition of 1400 ° C. × 1 hour in the air atmosphere,
A wall flow type particulate filter was obtained.

The obtained particulate filter (hereinafter, referred to as “high porosity layer forming filter”) had an average pore diameter of 50 μm and a porosity of 60% at the gas inflow side portion. As shown in FIG. 8, a high porosity heat insulating layer 76 having a thickness of 50 μm, an average pore diameter of 10 μm, and a porosity of 80% was formed on the gas outflow side portion of the cordierite substrate.

(Comparative Example 5) A wall flow type particulate filter having no heat insulating layer was prepared in the same procedure as in Example 10, except that the heat insulating material made of titania was not coated on the substrate surface and the inner wall surface of the trap chamber. (Hereinafter, referred to as “insulation material non-coated filter”).

A combustion test was performed on the particulate filters obtained in Examples 10 to 11 and Comparative Example 5,
The soot ignition temperature was measured. The combustion test was performed in Example 1.
Performed under the same conditions as Further, the ignition temperature was represented by an incoming gas temperature (° C.) when the amount of CO + CO ₂ in the exhaust gas reached 5 ppm. FIG. 9 shows the results.

The ignition temperature of the soot of the non-heat-insulating-coated filter obtained in Comparative Example 5 was 443 ° C. In contrast,
In the heat insulating material coated filter obtained in Example 10, the ignition temperature of soot was 420 ° C., and in the high porosity layer forming filter obtained in Example 11, the ignition temperature was 425 ° C.
The ignition temperature was reduced by about 20 ° C. as compared with Comparative Example 5.

From the above results, if a heat insulating layer is provided in the concave portion on the surface of the base material and the inside of the trap chamber, or a heat insulating layer having a higher porosity than the base material is provided in the gas outflow side portion of the base material, It was found that the depressions on the surface of the base material and the inside of the trap chamber, which are the combustion reaction fields, were insulated and the ignition temperature of the soot decreased.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the spirit of the present invention. . For example, in the above-described embodiment, the description has been given of the honeycomb filter. However, the average surface roughness Rz of the base material is set to be within a predetermined range, the trap chamber and the communication hole are provided inside the base material, and Providing a heat insulating layer in the portion can naturally be applied to a foam filter, a fiber filter, or the like, and the same effect as in the above embodiment can be obtained.

Further, the particulate filter according to the present invention can collect the particulates with high efficiency. Therefore, instead of burning the collected particulates with the oxygen remaining in the exhaust gas without burning the flame, the engine can be used. The air may be burned by an electric heater or the like while the air is being sent by the blower during the stop.

In the above embodiment, the wall flow type honeycomb filter provided with the trap chamber and the communication hole has been described. However, the trap chamber and the communication hole may be provided inside the base material of the straight flow type honeycomb filter. good.

If a trap chamber and a communication hole are provided inside the base material of the straight flow type honeycomb filter, when the exhaust gas passes near the surface of the base material, the flow of the exhaust gas is disturbed. Get inside. Therefore, as in the case of the wall flow type, the frequency of contact between the wall surface of the trap chamber and the particulates increases, and the collection efficiency and the combustion efficiency of the particulates can be improved.

Further, in the above embodiment, the heat insulating material coated filter to which only the method E is applied and the high porosity layer forming filter to which only the method F is applied have been described. However, in the case of the wall flow type honeycomb filter, , Method E
And the method F in combination. That is, a heat insulating material may be coated on the surface of the base material or the inner wall surface of the trap chamber, and a high porosity heat insulating layer may be provided on the gas outflow side. In this case, further improvement in combustion efficiency can be expected.

Instead of coating a heat insulating material made of a material having a smaller thermal conductivity and heat capacity than the substrate on the surface of the substrate and the inner wall of the trap chamber, the method F is applied, and pores are formed on the surface of the substrate and the inner wall of the trap chamber. A heat insulating layer having a high rate may be formed.

In the above embodiment, cordierite (thermal conductivity: 3.0 W / (m · K)) is used as a base material, and titania (TiO ₂ , thermal conductivity: 1.59 W) is used as a heat insulating layer.
/ (M · K)), but when the substrate is made of cordierite, silica (SiO ₂ , thermal conductivity: 1.38 W / (m · K)) is used as the heat insulating layer. May be used.

Further, in the particulate filter of the present invention, the recesses on the substrate surface and the inside of the trap chamber become a combustion reaction field by means of increasing the average surface roughness Rz or providing a trap chamber, so that the gas and the catalyst And the contact area increases.

For this reason, in addition to the particulate oxidation catalyst, a CO oxidation catalyst, a reduction catalyst for reducing NOx,
If the Ox storage material, the HC storage material, the thermal property control substance, and the like are carried on the surface of the base material and the inner wall surface of the trap chamber, it becomes possible to purify NOx, HC, CO, etc., as well as to remove and burn the particulates. When the fuel contains sulfur, titanium oxide or silica powder, which hardly reacts with sulfur, is used as a base material, and a porous zeolite for selecting and trapping hydrocarbons (HC) is added. You may do it.

[0159]

As described above, the particulate filter of the present invention comprises:
Since the average surface roughness Rz of the substrate is 30 to 1000 μm, there is an effect that the particulates in the exhaust gas are trapped in the concave portions on the substrate surface, and the collection efficiency of the particulates is improved. Further, since the frequency of contact between the particulates and the base material increases, there is an effect that the burning efficiency of the particulates is improved. Further, by setting the average surface roughness Rz of the base material within a predetermined range, there is an effect that an increase in pressure loss can be suppressed while maintaining a high particulate collection efficiency and a high combustion efficiency.

When a plurality of trap chambers and a communication hole connecting the trap chambers are provided inside the base material, the frequency of contact between the particulates and the base material increases, so that the combustion efficiency of the particulate filter increases. This has the effect.
In addition, the collection area of particulates increases,
Since the substrate is less likely to be clogged, there is an effect that the collection efficiency can be improved without increasing the pressure loss.

Further, if a heat insulating layer is provided on a part of the surface of the substrate, for example, a concave portion formed on the surface of the substrate, the inner wall surface of the trap, or the gas outflow side of the substrate, a combustion reaction field of the particulates is formed. Since the concave portion on the base material surface and the inside of the trap chamber are insulated, there is an effect that the burning efficiency of the particulate can be improved.

As described above, according to the particulate filter of the present invention, the particulates in the exhaust gas can be collected with high efficiency irrespective of the filter shape, and the particulates can be collected from a relatively low temperature range. Since flameless combustion is performed, if this is applied to, for example, a particulate filter for a diesel engine, a large amount of particulates generated when the exhaust gas temperature is low, such as when the engine is started or the engine is under low load operation, is used. It is not only capable of burning and removing curate, but also capable of purifying NOx and the like, and is an invention having an extremely large industrial effect.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the average surface roughness of a substrate and the combustion characteristics of soot.

FIG. 2 is a diagram showing the relationship between the average surface roughness of a substrate, the presence or absence of an oxidation catalyst, and the amount of CO + CO _{2 at} an inlet gas temperature of 400 ° C.

FIG. 3 is a partial cross-sectional view of a particulate filter having a trap chamber and a communication hole.

FIG. 4 is a view showing a process in which a communication hole is formed in a base material made of cordierite by using coarse talc.

FIG. 5 is a diagram showing a process of forming a communication hole in a base material made of cordierite by using a granulated powder made of alumina and kaolin.

FIG. 6 is a diagram showing the soot combustion characteristics of a particulate filter having a trap chamber and a communication hole, and a particulate filter having no trap chamber and a communication hole.

FIG. 7 is a partial sectional view of a heat insulating material coated filter.

FIG. 8 is a partial cross-sectional view of a high porosity layer forming filter.

9 is a diagram showing the ignition temperature of the heat insulating material coated filter shown in FIG. 7, the high porosity layer forming filter shown in FIG. 8, and the heat insulating material non-coated filter.

FIG. 10 is a cross-sectional view showing a state of use of a straight flow type particulate filter generally used in the related art.

FIG. 11 is a cross-sectional view illustrating a state of use of a wall flow type particulate filter conventionally generally used.

[Explanation of symbols]

Reference Signs List 30 particulate filter 32 base material 34 trap chamber 36 communication hole 60 particulate filter (heat insulating material coated filter) 62 base material 64 trap chamber 66 heat insulating layer 70 particulate filter (high porosity layer forming filter) 72 base material 74 trap chamber 76 Heat insulation layer (high porosity heat insulation layer)

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hiroshi Hojo 41-cho, Yokomichi, Nagakute-cho, Aichi-gun, Aichi Prefecture Inside of Toyota Central Research Laboratory Co., Ltd. (72) Inventor Koichiro Yamamoto 41, Yokomichi, Toyota Central Research Institute, Inc.

Claims (3)

[Claims] 1. A method for collecting particulates in exhaust gas,
A particulate filter for burning and removing the particulate filter, wherein a base material constituting the particulate filter has an average surface roughness Rz of 30 to 1000 µm. 2. The particulate filter according to claim 1, wherein the base material has a plurality of trap chambers and a communication hole connecting the trap chambers. 3. The particulate filter according to claim 1, wherein a heat insulating layer is provided on at least a part of the surface of the base material.