JP2003193820A - Ceramic honeycomb filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ceramic honeycomb filter for scavenging of exhaust particulates of a diesel engine of low pressure loss, high scavenging efficiency and high durability. <P>SOLUTION: This ceramic honeycomb filter constitutes its characteristic feature that a porous bulkhead of a ceramic honeycomb structural body 1 has more than 60% porosity and a more than 15 μm average pore diameter and that the maximum value of S<SB>n</SB>expressed under an expression (1) concerning inclination of an accumulated pore capacity distribution curve of the porous bulkhead 2 (curve expressed with a graph with a lateral axis as the pore diameter and a vertical axis as accumulated pore capacity) namely S<SB>n</SB>=-(V<SB>n</SB>-V<SB>n-1</SB>)/(log(D<SB>n</SB>)-log(D<SB>n-1</SB>)) (1), (where, D<SB>n</SB>is a pore diameter (μm) at a No.(n) measuring point, D<SB>n-1</SB>is a pore diameter (μm) at a No.(n-1) measuring point, V<SB>n</SB>is accumulated pore capacity (cm<SP>3</SP>/g) at the number (n) measuring point, V<SB>n-1</SB>is accumulated pore capacity (cm<SP>3</SP>/g) at the No.(n-1) measuring point and S<SB>n</SB>is inclination of the accumulated pore capacity distribution curve against the pore diameter at the No.(n) measuring point). <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic honeycomb filter for removing fine particles contained in exhaust gas of a diesel engine.

[0002]

2. Description of the Related Art In order to remove fine particles discharged from a diesel engine, a partition wall of a ceramic honeycomb structure has a porous structure, and the partition wall has a structure for allowing exhaust gas containing fine particles to pass therethrough (diesel). A study is underway to adopt a particulate filter). Regarding the characteristics of this filter, three are important: the efficiency of collecting fine particles, the pressure loss (pressure loss), and the time for collecting fine particles (the time from the start of collection to the time when a constant pressure loss is reached). Above all, the collection efficiency and the pressure loss are in a contradictory relationship,
If the collection efficiency is increased, the pressure loss increases and the collection time is shortened. If the pressure loss is decreased, the collection time can be increased but the collection efficiency is deteriorated. In order to satisfy these contradictory filter characteristics, the conventional technique for controlling the porosity, the average pore diameter, and the size of the pores existing on the partition wall surface is as follows for the ceramic honeycomb structure. Has been considered from.

In Japanese Patent Publication No. 3-10365, the pores existing on the surface of the filter partition wall are composed of small pores having a pore diameter of 5 to 40 μm and large pores having a pore diameter of 40 to 100 μm. It is disclosed that by configuring the number of holes to be 5 to 40 times the number of large holes, a collection efficiency can be maintained at a high value from the beginning, and an exhaust gas purification filter with low pressure loss can be obtained. On the other hand, the average pore diameter of the internal pores present inside the partition wall is larger than 15 μm, and the cumulative pore volume is 0.3 to 0.7 cm ³ / g, which is a preferable range. Here, although there is no description of the porosity P (volume%) of the partition wall,
True specific gravity ρ of cordierite materials described in the examples
Is 2.5 g / cm ³ , the cumulative pore volume V (cm ³
/ G) can be calculated by the following formula. P =
100 × V × ρ / (1 + V × ρ). Therefore, the preferable range of the cumulative pore volume of the internal pores existing inside the partition wall is 0.3 to
0.7 cm ³ / g is 42.8 to 6 in terms of porosity.
It becomes 3.6% by volume. (See Patent Document 1.) In Japanese Patent Publication No. 61-54750, a filter from a high collection rate type to a low collection rate type is controlled by controlling the open porosity (porosity) and the average pore diameter. It is disclosed that it can be designed. As a preferred specific example in the present publication, open porosity (porosity) and average pore diameter (average pore diameter) within a zone defined within a boundary connecting points 1-5-6-4 in FIG. 8 on page 20. ) Is described.
Here, point 1 is open porosity 58.5% by volume, average pore diameter 1 μm, point 5 is open porosity 39.5% by volume, average pore diameter 15 μm, point 6 is open porosity 62.0% by volume, average pore diameter 15 μm. , Point 4 is open porosity 90.0% by volume, average pore diameter 1 μm
Is. (See Patent Document 2.) And, in Japanese Patent Laid-Open No. 9-77573, the porosity is 55.
˜80%, the average pore diameter is 25 to 40 μm, and the pores on the partition wall surface are composed of small pores of 5 to 40 μm and large pores of 40 to 100 μm, and the number of the small pores is equal to the number of the large pores. It is disclosed that a honeycomb structure having properties of a high collection rate, a low pressure loss, and a low thermal expansion coefficient can be obtained by setting the ratio to 5 to 40 times. (See Patent Document 3.)

[0004]

[Patent Document 1] Japanese Patent Publication No. 3-10365

[Patent Document 2] Japanese Patent Publication No. 61-54750 (Fig. 8)

[Patent Document 3] Japanese Unexamined Patent Publication No. 9-77573

[0005]

However, although the porosity, the average pore diameter, and the size of the pores on the partition wall surface are optimized as shown in the above-mentioned prior art, the balance between the porosity and the collection efficiency can be achieved to some extent. Since the partition wall itself is a porous body, and the strength of the porous body has a contradictory relationship with its porosity and average pore diameter, the strength of the ceramic honeycomb structure is inevitably lowered. That is, as the porosity and the size of the pores increase, the strength of the ceramic honeycomb structure decreases. In particular, when the porosity is set to 60% or more or the average pore size is set to 15 μm or more in order to obtain a filter with low pressure loss, the strength is significantly reduced.
Therefore, both low pressure loss and high collection efficiency are achieved, and thermal stress and thermal shock stress generated when used as a particulate collection filter for diesel engines, mechanical tightening force during assembly, stress due to vibration, etc. Without being damaged by
There is a problem that a durable ceramic honeycomb filter cannot be obtained for a long period of time, which has been an obstacle to practical use of a diesel particulate filter.

In order to solve the above problems, the present invention has a partition wall having a porosity of 6 so that a filter with low pressure loss can be obtained.
Even if it is 0% or more and the average pore size is 15 μm or more, it will be damaged by thermal stress or thermal shock stress generated when it is used as a particulate collection filter of a diesel engine, mechanical tightening force during assembly, stress due to vibration, etc. It is an object of the present invention to provide a ceramic honeycomb filter having long-term durability.

[0007]

In order to solve the above problems, the present inventor has conducted diligent studies, and as a result, by setting the distribution of the pores formed in the partition walls of the honeycomb structure within a certain range, The inventors have found that a ceramic honeycomb filter satisfying the three characteristics of low pressure loss, high collection efficiency, and high strength can be obtained, and have arrived at the present invention. That is, the ceramic honeycomb filter of the present invention plugs the predetermined flow path end portion of the ceramic honeycomb structure, and allows the exhaust gas to pass through the porous partition walls that partition the flow path, so that In the ceramic honeycomb filter for removing fine particles contained therein, the porous partition walls have a porosity of 60% or more when measured by a mercury porosimetry method,
The following formula (1) S _n = − (V _n −V _n−1 ) / (log (D _n ) −) having an average pore diameter of μm or more and relating to the slope of the cumulative pore volume distribution curve of the porous partition walls. log (D _n-1 )) (1), (where D _n is the pore diameter (μ) at the (n) th measurement point.
m), D _n-1 is the pore diameter (μm) at the (n-1) th measurement point, and V _n is the cumulative pore volume (cm ³ / g) at the (n) th measurement point. Yes, V _n-1 is (n-
1) Cumulative pore volume at the measurement point (cm ³ / g)
And S _n is the slope of the cumulative pore volume distribution curve with respect to the pore diameter at the nth measurement point. ), The maximum value of S _n is 0.7 or more. At this time, the maximum value of S _n is preferably 0.9 or more, the porosity is 60 to 80%, and the average pore diameter is 15 to 40 μm.
It is preferable that it is m. Further, the chemical composition of the main component of the porous ceramics constituting the partition wall is SiO ₂ : 42
To 56 _{wt%, Al} 2 O 3: _30~45 wt%, Mg
It is preferable that O: 12 to 16 mass% and the main component of the crystal phase is cordierite. In addition, the ceramic honeycomb filter of the present invention plugs the predetermined flow path end portion of the ceramic honeycomb structure, and allows the exhaust gas to pass through the porous partition walls that partition the flow path, whereby A ceramic honeycomb filter for removing fine particles contained therein, wherein the surface of the porous partition wall and the catalyst are supported on the inside of the porous partition wall, wherein the porous partition wall is 60% when measured by mercury porosimetry. The following formula (1) S _n =-(V _n -V _n-1 ) / (log having the above porosity and an average pore diameter of 15 μm or more and relating to the slope of the cumulative pore volume distribution curve of the porous partition walls _{(D n) -log (D n} -1)) (1), ( where, D _n is (n) pore size (mu in th measurement point
m), D _n-1 is the pore diameter (μm) at the (n-1) th measurement point, and V _n is the cumulative pore volume (cm ³ / g) at the (n) th measurement point. Yes, V _n-1 is (n-
1) Cumulative pore volume at the measurement point (cm ³ / g)
And S _n is the slope of the cumulative pore volume distribution curve with respect to the pore diameter at the nth measurement point. ), The maximum value of S _n is 0.7 or more.

[0008]

Next, the function and effect of the present invention will be described.
It In the ceramic honeycomb filter of the present invention, the ceramic
The porous partition walls of the honeycomb structure are measured by mercury porosimetry.
60% or more of porosity, average of 15 μm or more
Pore diameter, cumulative pore volume distribution curve of the porous partition
(Graph with horizontal axis as pore diameter and vertical axis as cumulative pore volume
The following equation (1) regarding the slope of the curve   S_n=-(V_n-V_n-1) / (Log (D_n) -Log (D_n-1)) (1), (However, D_nIs the pore diameter at the (n) th measurement point (μ
m) and D_n-1At the (n-1) th measurement point
Pore size (μm), V_nAt the (n) th measurement point
Cumulative pore volume (cm^Three/ G) and V_n-1Is (n-
1) Cumulative pore volume (cm) at the 1st measurement point^Three/ G)
And S_nIs the pore size at the nth measurement point
It is the slope of the cumulative pore volume distribution curve. ) Represented by
S_nWith a maximum value of 0.7 or more,
The pore distribution becomes sharp and the average pore size
Since the percentage of holes is large, pressure loss can be kept low.
It is possible to maintain high strength as well as
is there. Here, the slope S of the cumulative pore volume distribution curve_nLimited
The reason for doing so will be described in detail. Ceramic honeycomb
The strength of the structure is affected by porosity and average pore size.
Of course, but it depends largely on the pore size distribution,
In particular, the pore size distribution should be sharp, in other words, the pore size
By improving the uniformity, the porosity is 60% or more,
Even if the average pore diameter is 15 μm or more, high strength can be obtained.
Because I found out Where porosity, average pore size,
Slope S of cumulative pore volume distribution curve_nMade by Micromeritics
Measured by mercury porosimetry using Autopore III 9410
did. In this mercury penetration method measurement, the sample for measurement
Is stored in the measuring cell, the pressure in the cell is reduced, and then the mercury is introduced.
Put in and pressurize.
From the relationship with the volume of mercury pushed into the pores,
Determine the relationship of cumulative pore volume. That is, the pressing force is large
And mercury penetrates into even finer pores, which is equivalent to the applied pressure.
The volume of the fine pores formed is measured. Therefore, the measurement
Are performed in order from those with large pores to those with small pores.
It At this time, the (n-1) th measurement point from the start of measurement
Pore size in_n-1, And the cumulative pore volume V_n-1When,
Pore diameter D at the (n) th measurement point_nAnd cumulative pore volume
V_nFrom the above, the value obtained by the above equation (1) is (n)
Slope S at eye measurement point_nBecomes S_nOf measurement results
An example is shown in FIG. In Figure 3, point a is the first and second
Pore size D at the measurement point₁, D_TwoAnd cumulative pore volume V
₁, V_TwoSlope obtained from₁[(V₁-V_Two) / (Lo
gD₁-LogD_Two)], And point b is the second and third
Pore size D at the measurement point_Two, D_ThreeAnd cumulative pore volume V
_Two, V_ThreeSlope obtained from_Two[(V_Two-V_Three) / (Lo
gD_Two-LogD_Three)]. Here, the details shown in FIG.
Pore diameter and slope S of cumulative pore volume distribution curve_nFrom the distribution of
_nIf the maximum value of is less than 0.7, the pore size distribution will be broad.
And S_nIf the maximum value of is 0.7 or more,
It can be seen that the cloth is very sharp. Pore size distribution
If it is broad, coarse pores that cause strength reduction,
The fine pores that cause clogging of fine particles and increase in pressure loss
The ratio decreases and it is difficult to achieve both low pressure loss and high strength.
_nWhen the maximum value of is 0.7 or more, the pore size distribution becomes shear.
Since the ratio of coarse pores and fine pores decreases,
Both pressure loss and high strength can be achieved. This is the cumulative pore volume
Slope of product distribution curve S_nBetween maximum value of A and compression ratio of A axis
It is also clear from FIG. , Where A-axis compression strength
The degree ratio is the A-axis compression strength calculated with the conventional product level as 1.0.
It is a relative value of degrees. S_nThe maximum value of becomes 0.7 or more
And the A-axis compressive strength is at the conventional level (for example, S_nMaximum value of
It can be seen that the value is 1.5 or more in a region of 0.6 or less).
That is, S_nWhen the maximum value of exceeds 0.7, the ceramic
Mechanical strength of honeycomb structure
I understand. To achieve both low pressure loss and high strength, S
_nThe maximum value of is more preferably 0.9 or more. Where sera
Limit the porosity of the Mick honeycomb structure to 60% or more
The reason is that if the porosity is less than 60%, the pressure loss of the filter is high.
Because it will be. If the porosity exceeds 80%,
The strength of the filter is reduced and the collection efficiency of fine particles is also improved.
Porosity is 60 to 80% in a preferable range because it deteriorates.
It Furthermore, the porosity of 65% or more reduces pressure loss.
The effect is even greater, with a porosity of 75% or less, strength and
Porosity of 65 can be obtained because the decrease in collection efficiency can be made smaller.
~ 75% is a more preferable range. Also ceramic
The average pore diameter of the pores existing in the honeycomb structure is 15μ
It is limited to m or more when the average pore size is less than 15 μm.
This is because the pressure loss of the filter becomes large.
If the average pore size exceeds 40 μm, the filter
As the strength decreases, small particles are not captured and
Since it passes through the filter and the collection efficiency deteriorates
A pore size of 15 to 40 μm is a preferable range. Furthermore, flat
If the uniform pore size is 25 μm or less, the strength and the collection efficiency will be reduced.
Since it can be made small, the average pore diameter of 15 to 25 μm is low.
It is possible to achieve both pressure loss and high strength, which are contradictory properties.
This is a more preferable range.

In the ceramic honeycomb filter of the present invention, the chemical composition of the main component of the porous ceramics constituting the partition walls of the honeycomb structure is SiO ₂ : 42-5.
6 mass%, Al ₂ O ₃ : 30 to 45 mass%, MgO: 1
It is preferable that the main component of the crystal phase is cordierite at 2 to 16% by mass, because the low thermal expansion property originally possessed by cordierite is utilized and cracks are less likely to occur even when a thermal shock is applied. This is because a honeycomb filter can be obtained, but the present invention is not limited to this,
Other heat-resistant ceramics such as mullite, alumina, silicon nitride, silicon carbide, aluminum nitride, lithium aluminum silicate, aluminum titanate, zirconia, etc. can be used.

Further, in the ceramic honeycomb filter in which the catalyst is supported on the surface of the porous partition wall and inside the porous partition wall, the porous partition wall of the ceramic honeycomb structure has a porosity of 60% or more when measured by the mercury intrusion method, 15
The following formula relating to the slope of the cumulative pore volume distribution curve (the curve represented by the graph in which the horizontal axis is the pore diameter and the vertical axis is the cumulative pore volume) having an average pore diameter of μm or more and the porous partition walls _{(1) S n = - (} V n -V n-1) / (log (D n) -log (D n-1)) (1), in (where, D _n is (n) th measurement point Pore size (μ
m), D _n-1 is the pore diameter (μm) at the (n-1) th measurement point, and V _n is the cumulative pore volume (cm ³ / g) at the (n) th measurement point. Yes, V _n-1 is (n-
1) Cumulative pore volume at the measurement point (cm ³ / g)
And S _n is the slope of the cumulative pore volume distribution curve with respect to the pore diameter at the nth measurement point. Since the maximum value of S _n is 0.7 or more represented by), the low pressure loss as described above, a high collection efficiency, the effect of both high strength, partition wall surface and the catalyst supported inside the partition wall This is because it is remarkable in the existing ceramic honeycomb filter.

The ceramic honeycomb structure of the present invention can be manufactured as follows. First, the ceramic raw material powder should have an average particle size of 20 μm or more, especially a particle size of 20-
A pore-forming material in which 100 μm accounts for 50% or more is added in a range where the porosity after firing is 60 to 80%. If necessary, a molding aid such as a binder and a lubricant is added to this mixture, and after mixing, water is added to prepare a plasticizable batch. After extruding a honeycomb structure molded body from this batch by a known extrusion molding method, drying, burning removal of the pore-forming material, and firing are performed to remove fine pores peculiar to the ceramics in the partition walls and the pore-forming material after combustion removal. A honeycomb structure having pores formed by the traces of 1 is obtained. In this way, a pore-forming material having a particle size equal to that of the fine pores originally possessed by ceramics (average particle size of 20 μm or more, particle size of 20 to 100 μm).
The average pore diameter of the partition walls can be set in the range of 15 to 25 μm by the combination with the pores formed by (m occupies 50% or more), and the maximum value of Sn indicating the sharpness of the pore distribution is obtained. Can be 0.7 or more.
In particular, cordierite ceramics are originally 1-20
Since it has pores with a pore size of about μm, the average particle size is 20 μm.
As described above, the combination with the pore-forming material having a particle size of 20 to 100 μm accounting for 50% or more is effective. The pore-forming material is known graphite, wheat flour, resin powder or the like, and has an average particle size of 20.
It is preferable to perform classification so that the particle size distribution is such that the particle size is not less than μm and the particle size is 20 to 100 μm occupying 50% or more. When resin powder is used, the production conditions may be adjusted to obtain a particle size distribution in which the average particle size is 20 μm or more and the particle size of 20 to 100 μm accounts for 50% or more. Further, when the pore-forming material is substantially spherical, the pores formed in the partition walls are also substantially spherical, so that stress concentration on the pores can be reduced, and the ceramic honeycomb has excellent mechanical strength. It is preferable because a structure can be obtained. Furthermore, if the pore-forming material is hollow, it is possible to easily remove the pore-forming material from the partition wall when burning and removing the pore-forming material, and the problem of cracking of the partition wall during combustion removal is unlikely to occur. It is preferable because the yield is improved.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The actual examples of the present invention will be described below, but the present invention is not limited thereto. (Example 1) SiO ₂ is 42 to 56 wt%, _Al 2 _{O 3}
Of 30% to 45% by mass and 12% to 16% by mass of MgO in a cordierite-ceramic raw material powder such as kaolin, calcined kaolin, alumina, aluminum hydroxide, silica, talc, etc. No. A predetermined amount of each of the three types of spherical resin powders 1 to 3 was mixed. At this time, the particle size distribution of the spherical resin powder used as the pore former is shown in FIG.
The ratio of the particle size of m is shown in Table 1. Next, water was added to this mixture to prepare a plasticizable batch, and this batch was molded into a cylindrical honeycomb structure by a known extrusion molding method. Then, the molded body is dried and then 1380 to 142
After firing in a temperature range of 0 ° C., as shown in the front view and the side view of FIGS. 1 (a) and 1 (b), the porous ceramic partition walls 3 and the through holes 2 are formed. Test N corresponding to 1-3
o. Three types of cordierite-based ceramic honeycomb structures 1 to 1 were obtained. The obtained honeycomb structure has a diameter of 143 mm, a length of 152 mm, and a partition wall thickness of 0.3 m.
The number of channels per m, 1 cm ² was 46.

The obtained test No. 1 to 3 types of code
Porosity, average of jellite ceramic honeycomb structure
Pore diameter, slope S of cumulative pore volume distribution curve_nMicromerit
Mercury injection method using Autopore III 9410 manufactured by ics
It was measured at. The value obtained by the measurement is the mercury added to the sample.
Pressure and the volume of mercury injected into the sample,
Pore diameter D at the (n) th measurement point_nFrom equation (2),
Cumulative pore volume V at the (n) th measurement point_nIs from equation (3)
I calculated. Pore diameter D at the (n) th measurement point_n= -4α cos θ / Pn (2) Here, α is the surface tension of mercury (4.935 × 10 −4).
kg / cm) θ is the contact angle between mercury and solid (130 °) Pn is the pressure of mercury at the (n) th measurement point. Cumulative pore volume V at the (n) th measurement point_n= V_n/ W (3) Where v_nIs pressed into the sample at the (n) th measurement point.
The volume w of the prepared sample is the weight of the sample. Obtained pores
The relationship between diameter and cumulative pore volume (cumulative pore volume distribution curve)
As shown in FIG. As is clear from FIG. 6, about 10 μm to about
Test No. between 100 μm. 1 honeycomb structure
The slope of the product pore volume distribution curve is very steep, and the test N
o. Slope of cumulative pore volume distribution curve for honeycomb structure 2
Is steep, but the test No. Accumulation of 3 honeycomb structures
The slope of the pore volume distribution curve was relatively gentle. the above
From the cumulative pore volume distribution curve shown in FIG. 1
To Slope 3 of the cumulative pore volume distribution curve of the honeycomb structures of
_nI asked. Slope S of cumulative pore volume distribution curve_nIs the measurement
Obtain a smooth trendline from the data plot and
It should be obtained as the differential value of the pore size on the line at a minute interval.
However, as is clear from Fig. 6, the cumulative pores
The distribution curve is sufficiently smooth, and the measurement points are
Logarithm (logD_n) Are substantially equidistant
At the (n) th measurement point and the (n-1) th measurement point
From the measured pore diameter and cumulative pore volume, the slope S
_nThere is almost no error in obtaining. Obtained in this way
Of the pore diameter and cumulative pore volume distribution curve of each honeycomb structure
The relationship of the slope Sn is shown in FIG. Cumulative pore volume distribution in Figure 6
Test No. with the steepest slope in the curve 1 honeycomb
The Sn of the structure was the highest, and the test was the steepest.
S of 2 honeycomb structure_nIs next highest and the slope is relatively gentle
The test No. S of the honeycomb structure of 3_nIs the most
Was also small. The maximum value of Sn obtained in this way, and
Table 2 shows the measurement results of porosity and average pore diameter.

[0014]

[Table 1]

The end faces of the ceramic honeycomb structure produced as described above are plugged with a sealing material 5 as shown in the front view and side view of FIGS. 2 (a) and 2 (b), and a porous ceramic honeycomb is formed. Got a filter. The filter characteristics of the obtained porous ceramic honeycomb filter,
The pressure loss and breakage resistance were evaluated. The results are shown together in Table 2. Here, the pressure loss is evaluated by the pressure loss before and after the honeycomb filter inflows when a predetermined flow rate of air is flown in a pressure loss test stand, and if the pressure loss is a practically allowable value or less, If the pressure loss exceeds the practically acceptable pressure loss, it is judged as pass (○), and it is judged as unacceptable (x). The breakage resistance is evaluated by the value of the A-axis compressive strength ratio, and if the conventional product level is 1.0 and the value is 1.5 or more, it is judged as (◯), and if 2.0 or more is preferable, ( ◎), if less than 1.5 is rejected (x)
Indicated by. The measurement of the A-axis compressive strength was performed according to the standard M505-87 "Testing method of ceramic monolithic carrier for automobile exhaust gas purification catalyst" defined by the Society of Automotive Engineers of Japan. Then, as a comprehensive judgment, those in which both the pressure loss and the breakage resistance are passed (○), and when there is a (◎) judgment among them (⊚), those in which any one is not passed (×) ).

[0016]

[Table 2]

Among the results shown in Table 2, the test No. which is an example of the present invention. In the ceramic honeycomb filters shown in 1-2, since the maximum value of the slope S _n in the cumulative pore volume distribution curve is 0.7 or more, the porous material having a porosity of 60% or more and an average pore diameter of 15 μm or more. However, the pressure loss was low, the damage resistance was also passed, and the overall judgment was (◯) and (⊚). On the other hand, among the results shown in Table 2, in the ceramic honeycomb filter shown in Test No. 3 of the comparative example, the maximum value of the slope S _n in the cumulative pore volume distribution curve was less than 0.7, so the pressure loss Passed, but the damage resistance was unacceptable (x), and the overall judgment was (x). As is clear from the results of Table 2 above, when comprehensively judging from the results of pressure loss and damage resistance, which are important characteristics as a filter for collecting particulates, the test No., which is an example of the present invention. All of the ceramic honeycomb filters 1 and 2 were filters satisfying the pressure loss characteristics and the breakage resistance.

(Example 2) Test No. 1 of Example 1 A plasticizable batch similar to that of No. 1 was prepared, and this batch was molded into a cylindrical honeycomb structure by a known extrusion molding method.
At this time, the dimensions of a known mold were adjusted so that various partition wall thicknesses and the number of flow paths per cm ² could be obtained. Next, this molded body was dried and then fired in a temperature range of 1380 to 1420 ° C. to obtain various cordierite ceramic honeycomb structures 1 including the porous ceramic partition walls 3 and the through holes 2. The obtained honeycomb structure had a diameter of 143 mm and a length of 152 mm, and the test No. As shown in 4 to 8, the wall thickness of the partition wall was 0.15 mm to 0.33 mm, and the number of channels per cm ² was 39 to 62, which were five types. Hereinafter, in the same manner as in Example 1, after sealing the end face,
The pressure loss and breakage resistance, which are filter characteristics, were measured. The results are shown in Table 3. The test No. 4-
In each of the 8 types, the porosity is 65% and the average pore diameter is 20.8.
%, The maximum value of the slope S _n in the cumulative pore volume distribution curve was 1.12.

[0019]

[Table 3]

As shown in Table 3, Test N which is an example of the present invention.
o. The ceramic honeycomb filters shown in Nos. 4 to 8 were all judged to have a filter characteristic of (◯) or (⊚) regardless of the partition structure.

Example 3 Test N used in Example 1
o. For the ceramic honeycomb filters 1 to 3, a catalyst was supported on the partition wall surface and inside as follows.

As a material having a high specific surface area, activated alumina having a central particle diameter of 5 μm and alumina sol were mixed with water, and the obtained activated alumina slurry was wash-coated with the obtained filter. After that, remove the excess slurry and repeat the coating to obtain a coating amount of 60g / L.
A filter was manufactured. Then, after drying at 120 ° C., baking at 800 ° C., immersion in an aqueous solution of chloroplatinic acid, drying at 120 ° C., baking at 800 ° C.,
A ceramic honeycomb filter supporting platinum was obtained.
The amount of platinum supported at this time was about 2 g / L.

With respect to the filter of the ceramic honeycomb filter after carrying the catalyst, the pressure loss was measured by the same method as in Example 1. Furthermore, when a predetermined amount of carbon is charged at a predetermined flow rate in a pressure loss test stand and the carbon is captured by the honeycomb filter, a pressure loss difference ΔP before and after carbon capture (pressure loss after carbon capture-before carbon capture Pressure loss) and measure the pressure loss difference Δ
If P is less than or equal to a practically acceptable value, it is judged as acceptable (○).
Then, if the pressure loss exceeds a practically allowable value, it is determined as a failure and indicated by (x). The results are shown together in Table 4.

[0024]

[Table 4]

Among the results shown in Table 4, Test No. which is an example of the present invention. The ceramic honeycomb filters shown in 1-2 are
Almost no increase in pressure loss due to catalyst loading was observed, and all pressure loss results were acceptable (◯). On the other hand, test No. which is a comparative example. In the ceramic honeycomb filter shown in FIG. 3, an increase in pressure loss was observed due to the catalyst loading, and the result of the pressure loss was disapproved (x). Moreover, the test No. which is an example of the present invention. The ceramic honeycomb filters shown in FIGS. 1 and 2 pass (◯) when the pressure loss difference ΔP before and after capturing carbon is less than a practically permissible value. In the honeycomb filter shown in FIG. 3, ΔP exceeded the practically allowable value and was rejected (x). As mentioned above,
The maximum value of the slope S _n in the cumulative pore volume distribution curve is 0.
It is obvious that the ceramic honeycomb filter having the number of 7 or more shows excellent filter performance with little increase in pressure loss and increase in pressure loss due to carbon capture even after the catalyst is supported.

[0026]

According to the present invention, the maximum value of the slope S _n in the cumulative pore volume distribution curve of the pores in the partition walls of the ceramic honeycomb structure forming the ceramic honeycomb filter is set to 0.7 or more. , Porosity of 60% or more,
Even when the average pore diameter is as high as 15 μm or more, when used as a diesel particulate filter, it is possible to achieve both properties of low pressure loss and high collection efficiency, which are contradictory properties. Moreover, it is possible to obtain a ceramic honeycomb filter having excellent durability that is not damaged by thermal stress or thermal shock stress during use, mechanical tightening force during assembly, or stress due to vibration.

[Brief description of drawings]

1A and 1B are a front view and a side view, respectively, showing an example of a honeycomb structure.

2A and 2B are a front view and a side view showing an example of a filter using a honeycomb structure.

FIG. 3 is a graph showing an example of the relationship between the pore diameter obtained by the mercury porosimetry method and the slope S _n of the cumulative pore volume distribution curve.

FIG. 4 is an example graph showing the relationship between the maximum value of the slope S _n of the cumulative pore volume distribution curve and the A-axis compressive strength ratio.

5 is a graph showing the particle size distribution of the pore-forming material used in Example 1. FIG.

6 is a test No. 1 in Example 1. FIG. It is a graph which shows the relationship between the pore diameter of 1 to 3 test pieces and a cumulative pore volume.

7 is a test No. in Example 1. FIG. Is a graph showing pore diameter of 1-3 specimens and the relationship between the slope S _n of a cumulative pore volume distribution curve.

[Explanation of symbols]

1: ceramic honeycomb structure, 2: partition walls, 3: through holes, 4: ceramic honeycomb filter, 5: sealing material,
a: slope S ₁ obtained from the first and second measurement results on the cumulative pore volume distribution curve, b: slope S ₂ obtained from the second and third measurement results on the cumulative pore volume distribution curve,

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[Procedure amendment]

[Submission date] April 15, 2003 (2003.4.1)
5)

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be amended] Claims

[Correction method] Change

[Correction content]

[Claims]

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0007

[Correction method] Change

[Correction content]

[0007]

In order to solve the above problems, the present inventor has conducted diligent studies, and as a result, by setting the distribution of the pores formed in the partition walls of the honeycomb structure within a certain range, The inventors have found that a ceramic honeycomb filter satisfying the three characteristics of low pressure loss, high collection efficiency, and high strength can be obtained, and have arrived at the present invention. That is, the ceramic honeycomb filter of the present invention, ceramic
A raw material powder with an average particle size of 20 μm or more and a particle size of 20 to 10
For pore-forming material, water, etc. having a particle size distribution of 0 μm of 50% or more
Obtained by extrusion-molding, mixing, and mixing batches, drying and firing
By plugging the predetermined flow passage end portion of the ceramic honeycomb structure, allowed to pass through the exhaust gas porous partition walls separating the flow path for a ceramic honeycomb filter for removing fine particles contained in the exhaust gas In the above, the porous partition wall has a porosity of 60% or more and an average pore diameter of 15 μm or more when measured by a mercury porosimetry method, and the following formula (1) regarding the slope of the cumulative pore volume distribution curve of the porous partition wall is used. _{) S n = - (V n} -V n -1) / (log (D n) -log (D n-1)) (1), ( where, D _n is (n) pore size in th measurement point (Μ
m), D _n-1 is the pore diameter (μm) at the (n-1) th measurement point, and V _n is the cumulative pore volume (cm ³ / g) at the (n) th measurement point. Yes, V _{n -1} is (n-
1) Cumulative pore volume at the measurement point (cm ³ / g)
And S _n is the slope of the cumulative pore volume distribution curve with respect to the pore diameter at the nth measurement point. ), The maximum value of S _n is 0.7 or more. At this time, the maximum value of S _n is preferably 0.9 or more, the porosity is 60 to 80%, and the average pore diameter is 15 to 40 μm.
It is preferable that it is m. Further, the chemical composition of the main component of the porous ceramics constituting the partition wall is SiO ₂ : 42
To 56 _{wt%, Al} 2 O 3: _30~45 wt%, Mg
It is preferable that O: 12 to 16 mass% and the main component of the crystal phase is cordierite. Further, the ceramic honeycomb filter of the present invention, the ceramic raw material powder, the average particle
Particles with a diameter of 20 μm or more and a particle size of 20 to 100 μm of 50% or more
A batch in which a pore-forming material having a degree distribution, water, etc. are added and mixed,
After extrusion molding, drying, by plugging the predetermined flow path end portion of the ceramic honeycomb structure obtained by firing, by allowing the exhaust gas to pass through the porous partition walls that partition the flow path,
A ceramic honeycomb filter for removing fine particles contained in exhaust gas, wherein the surface of the porous partition wall and a ceramic honeycomb filter in which a catalyst is carried inside the porous partition wall, the porous partition wall was measured by a mercury injection method. In this case, the porosity is 60% or more, the average pore diameter is 15 μm or more, and the following formula (1) S _n = − (V _n −V _{n −1} ) relating to the slope of the cumulative pore volume distribution curve of the porous partition walls is obtained. ) / (Log (D _n ) -log (D _n-1 )) (1), (where D _n is the pore diameter (μ) at the (n) th measurement point.
m), D _n-1 is the pore diameter (μm) at the (n-1) th measurement point, and V _n is the cumulative pore volume (cm ³ / g) at the (n) th measurement point. Yes, V _{n -1} is (n-
1) Cumulative pore volume at the measurement point (cm ³ / g)
And S _n is the slope of the cumulative pore volume distribution curve with respect to the pore diameter at the nth measurement point. ), The maximum value of S _n is 0.7 or more.

Continued front page    (72) Inventor Hiroshi Funabashi             3-1, Hinodai, Hino City, Tokyo 1 Hino             Inside the automobile corporation (72) Keiichi Nakagome             3-1, Hinodai, Hino City, Tokyo 1 Hino             Inside the automobile corporation (72) Inventor Makoto Tsujida             3-1, Hinodai, Hino City, Tokyo 1 Hino             Inside the automobile corporation (72) Inventor Hisashi Tohsaka             3-1, Hinodai, Hino City, Tokyo 1 Hino             Inside the automobile corporation F-term (reference) 3G090 AA02                 4D019 AA01 BA05 BB06 BD01 CA01                       CB04 CB06                 4D058 JA32 JB06 SA08                 4G019 FA12 FA13

Claims (6)

[Claims] 1. A fine particle contained in the exhaust gas is removed by plugging a predetermined flow path end of the ceramic honeycomb structure and passing the exhaust gas through a porous partition wall that defines the flow path. In the ceramic honeycomb filter according to the present invention, the porous partition walls have a porosity of 60% or more and an average pore diameter of 15 μm or more when measured by the mercury porosimetry method, and the cumulative partition walls of the partition walls with respect to the pore diameter at the n-th measurement point. The maximum value of the slope S _n of the pore volume distribution curve is 0.7 or more, and the slope S _n of the cumulative pore volume distribution curve is _expressed by the following formula (1) S _n =-(V _n -V _n-1 ) / (Log (D _n ) −log (D _n−1 )) (1), (where D _n is the pore diameter (μ) at the (n) th measurement point.
m), D _n-1 is the pore diameter (μm) at the (n-1) th measurement point, and V _n is the cumulative pore volume (cm ³ / g) at the (n) th measurement point. Yes, V _n-1 is (n-
1) Cumulative pore volume at the measurement point (cm ³ / g)
Is. ), A ceramic honeycomb filter. 2. The ceramic honeycomb filter according to claim 1, wherein the maximum value of the slope S _n in the cumulative pore distribution volume curve of the porous partition walls is 0.9 or more. 3. The porosity of the porous partition wall is 60 to 80%.
The ceramic honeycomb filter according to claim 1 or 2, wherein 4. The average pore diameter of the porous partition walls is 15 to 4
The ceramic honeycomb filter according to claim 1, wherein the ceramic honeycomb filter has a thickness of 0 μm. 5. The chemical composition of the main component of the porous ceramics constituting the porous partition walls is SiO ₂ : 42 to 56 mass%, Al ₂ O ₃ : 30 to 45 mass%, MgO: 12 to 1
The ceramic honeycomb filter according to any one of claims 1 to 4, wherein the main component of the crystal phase is cordierite at 6% by mass. 6. A fine particle contained in the exhaust gas is removed by plugging a predetermined flow path end portion of the ceramic honeycomb structure and passing the exhaust gas through a porous partition wall that defines the flow path. In the ceramic honeycomb filter, wherein the surface of the porous partition wall and the catalyst are supported on the inside of the porous partition wall, the porous partition wall is 60% when measured by mercury porosimetry.
It has the above porosity and an average pore diameter of 15 μm or more, and the maximum value of the slope S _n of the cumulative pore volume distribution curve of the partition walls with respect to the pore diameter at the nth measurement point is 0.7 or more,
The slope S _n of the cumulative pore volume distribution curve is _expressed by the following formula (1) S _n = − (V _n −V _n−1 ) / (log (D _n ) −log (D _n−1 )) (1), (However, D _n is the pore diameter at the (n) th measurement point (μ
m), D _n-1 is the pore diameter (μm) at the (n-1) th measurement point, and V _n is the cumulative pore volume (cm ³ / g) at the (n) th measurement point. Yes, V _n-1 is (n-
1) Cumulative pore volume at the measurement point (cm ³ / g)
Is. ), A ceramic honeycomb filter.