JP2021159888A - Ceramic honeycomb structure - Google Patents

Abstract

To provide a ceramic honeycomb structure which has a lowered pressure loss and effectively catches the nano-sized PM occupying a large portion of PM particles in an exhaust gas.SOLUTION: An objective ceramic honeycomb structure has a plurality of flow channels formed by a porous barrier 2, has total pore volume of 0.70-0.80 cm3/g in the pore distribution of a barrier 2, and has in particular: 0.68-0.78 cm3/g of the pore volume of 1 μm or more; 0.65-0.75 cm3/g of that of 2 μm or more; 0.58-0.68 cm3/g of that of 5 μm or more; 0.42-0.56 cm3/g of that of 10 μm or more; 0.06-0.19 cm3/g of that of 20 μm or more; 0.03-0.10 cm3/g of that of 30 μm or more; 0.02-0.05 cm3/g of that of 50 μm or more; 0.010-0.035 cm3/g of that of 100 μm or more; and 0.020 cm3/g or less of that of 200 μm or more.SELECTED DRAWING: Figure 1

Description

The present invention is a ceramic honeycomb for purifying exhaust gas by removing particulate matter (particulate matter (hereinafter, may be referred to as "PM")) in exhaust gas emitted from an internal combustion engine such as a diesel engine. The present invention relates to a ceramic honeycomb structure used for a filter, particularly a ceramic honeycomb filter for removing fine particles (so-called nanoparticles) having a particle size of 50 nm or less.

If NOx and PM (Particulate Matter) contained in the exhaust gas of a diesel engine are released into the atmosphere, it may adversely affect the human body and the environment. In addition, a honeycomb structure carrying a NOx catalyst and a ceramic honeycomb filter for collecting PM have been conventionally mounted. Fig. 1 and Fig. 2 show an example of a ceramic honeycomb filter for collecting PM in the exhaust gas and purifying the exhaust gas. The ceramic honeycomb filter 10 includes a ceramic honeycomb structure composed of a porous partition wall 2 forming a large number of flow paths 3 and 4 and an outer peripheral wall 1, and exhaust gas inflow side end faces 8 and outflow side end faces of the flow paths 3 and 4. It consists of an inflow side sealing part 6a and an outflow side sealing part 6c that alternately seal 9 in a checkered pattern.

In the ceramic honeycomb filter 10, the exhaust gas flows in from the outflow side sealing flow path 3 opened in the exhaust gas inflow side end surface 8 and exists on the surface and inside of the partition wall 2, as shown by the dotted line arrow in FIG. PM in the exhaust gas is collected and the exhaust gas is purified when passing through the communication hole. The purified exhaust gas flows out from the inflow side sealing flow path 4 opened in the exhaust gas outflow side end face 9, and is released into the atmosphere.

If PM continues to be collected in the partition wall 2, the communication holes on the surface and inside of the partition wall are clogged by the PM, and the pressure loss when the exhaust gas passes through the ceramic honeycomb filter increases. Therefore, it is necessary to burn and remove PM before the pressure loss reaches a specified value to regenerate the ceramic honeycomb filter. The ceramic honeycomb filter needs to satisfy a high collection rate of fine particles and a low pressure loss, but since the two are in a contradictory relationship, the porosity, the pore volume, and the size of the pores existing on the partition wall surface Conventionally, a technique for controlling the above and satisfying both of them has been studied.

Patent Document 1 describes that a cordierite ceramic product has porosity, median pore diameter (d50), and average thermal expansion coefficient (CTE) of 25 to 800 ° C., and the porosity is ≥64% and <80. %, And the median porosity (d50) and the CTE are in the following range: (i) ≥ 10 μm and <18 μm median porosity (d50), the CTE is <6.0 × 10 ^-7 / ° C, ( ii) At ≥18 μm and <22 μm median porosity (d50), CTE is <9.0 × 10 ^-7 / ° C, (iii) at ≥22 μm and ≤25 μm median porosity (d50), CTE is <10.0. At ^{x10 -7} / ° C, (iv)> 25 μm and <29 μm median porosity (d50), CTE is <13.0 × 10 ^-7 / ° C, or (v) ≥29 μm and ≤45 μm median porosity (d50) discloses a cordierite ceramic product characterized in that the CTE falls within one of <17.0 × 10 ^-7 / ° C and ≧ 3.0 × 10 ^{-7 / ° C.} Further, the present invention provides a cordierite ceramic body having high porosity and median coarse pore diameter for low pressure drop even with a catalyst, and at the same time having a CTE average value that guarantees an improved combination of thermostable impact resistance and strength. It is stated that.

Patent Document 2 describes a ceramic honeycomb structure having a large number of flow paths partitioned by a porous partition wall, wherein the partition wall has (a) a porosity of 55 to 80% and (b) a mercury press-fitting method. The measured median pore diameter D50 is 5 to 27 μm, (c) the opening area ratio of the pores opened on the surface is 20% or more, and (d) the area standard when the pores opened on the surface are represented by the equivalent circle diameter. The median opening diameter d50 is 10 to 45 μm, (e) the equivalent circle diameter of the pores opened on the surface is 10 μm or more and less than 40 μm, and the pore density is 350 cells / mm2 or more. The maximum value of the slope of the curve showing the cumulative pore volume with respect to the pore diameter as measured by is 1.6 or more, and (g) the ratio D50 / d50 of the median pore diameter D50 to the median opening diameter d50 is 0.65 or less. A ceramic honeycomb structure characterized by the above is disclosed. Then, even in the state before PM is deposited, nanoparticles that greatly affect the number of discharged particles are effectively collected, the collection rate based on the number of PM particles is improved, and PM is collected. It is described that the degree of deterioration of the pressure loss characteristic when accumulated is reduced.

Patent Document 3 describes a cordierite ceramic honeycomb structure having a large number of flow paths partitioned by a porous partition wall, wherein the partition wall has (a) a porosity of more than 65% and 75% or less. (b) In the pore distribution measured by the mercury intrusion method, (i) the cumulative pore volume (the cumulative value of the pore volume from the maximum pore diameter to the specific pore diameter) is 10% of the total pore volume. Porosity d10 is less than 50 μm, 50% pore diameter (median pore diameter) d50 is 18 μm or more and 27 μm or less, 90% pore diameter d90 is 10 μm or more, and (d10-d90) / d50 is 2.3 or less. (Ii) The difference between the log of the pore diameter d20 where the cumulative pore volume is 20% of the total pore volume and the log of the pore diameter d80 which is 80% is σ = log (d20) -log (d80). It is 0.25 or less, and (iii) the slope of the curve indicating the cumulative pore volume with respect to the pore diameter S _n =-(V _n -V _n-1 ) / (log (d _n ) -log (d _n-1 )) [ However, d _n and V _n are the pore diameter and cumulative pore volume at the nth measurement point, respectively, and d _n-1 and V _n-1 are the pore diameter and cumulative fineness at the (n-1) th measurement point, respectively. A cordierite ceramic honeycomb structure characterized in that the maximum value of [pore volume] is 3 or more is disclosed. Then, in order to use it as a carrier of an SRC catalyst having excellent purification efficiency of nitrogen oxides, the amount of the catalyst substance supported per unit volume is increased without increasing the pressure loss, and the exhaust gas and the catalyst substance are used. It is described that the contact efficiency of the gas can be increased.

In addition, there are many so-called nanoparticles having a particle size of 50 nm or less in PM. These nanoparticles have a higher deposition rate in the respiratory system when inhaled into the body than when inhaled larger particles of the same mass. Further, since nanoparticles have a relatively large surface area per volume, when toxic chemical substances are adsorbed on the particle surface, they may become PM particles having stronger toxicity. And since the number of nanoparticles contained in PM is small in terms of mass, the current regulation based on PM mass is not sufficient, and as a future emission regulation, the emission of nanoparticles that greatly affects the number of emitted particles The introduction of the standard (PM particle number standard) for suppressing the problem is being promoted. When this standard is established, in addition to excellent pressure drop characteristics, the honeycomb filter improves the collection rate based on the number of PM particles, especially the number of nanoparticlees, rather than the collection rate based on the current PM mass standard. Is required.

Patent Document 4 describes a ceramic honeycomb structure having a large number of flow paths partitioned by a porous partition wall, wherein the partition wall has (a) a porosity of 50 to 60% and (b) a mercury press-fitting method. In the measured pore distribution, (i) the pore diameter d5 at which the cumulative pore volume is 5% of the total pore volume is 22 μm or more and less than 55 μm, and the pore diameter d10 at 10% is 15 to 35 μm or 50%. Porosity d50 is 10 to 20 μm, 85% pore diameter d85 is 5 to 9 μm, 90% pore diameter d90 is 3 to 8 μm, 98% pore diameter d98 is 2.5 μm or less, ( d10-d90) / d50 is 1.3 to 1.8, (d50-d90) / d50 is 0.45 to 0.75, and (d10-d50) / d50 is 0.75 to 1.1, and (ii) cumulative pore volume is total pore volume. A ceramic honeycomb structure in which the difference σ = log (d20) -log (d80) between the logarithm of the pore diameter d20 which is 20% and the logarithm of the pore diameter d80 which is 80% is 0.39 or less is disclosed. Even in the state before PM is deposited at the beginning of use (when the ceramic honeycomb filter is used from an unused state or when it is used again after being regenerated), it greatly affects the number of particles in the exhaust gas. It is described that the nano-sized PM can be effectively collected, the collection rate based on the number of PM particles is improved, and the pressure loss characteristic when the PM is collected is not deteriorated.

Patent Document 5 describes a ceramic honeycomb structure having a large number of flow paths partitioned by a porous partition wall, wherein the partition wall has (a) a porosity of 50 to 63% and (b) a mercury intrusion method. In the measured pore distribution, (i) the pore diameter d2, which is 2% of the total pore volume, is more than 180 μm and 250 μm or less, and the pore diameter d5, which is 5%, is 55 to 150 μm, 10%. Porosity d10 is 17-40 μm, 50% pore diameter (median pore diameter) d50 is 10-20 μm, 85% pore diameter d85 is 5.5-10 μm, 90% pore diameter d90 is 3.5-9 μm, 98 The pore diameter d98 that is% is 2.5 μm or less, (d10-d90) / d50 is 1.3 to 2, (d50-d90) / d50 is 0.45 to 0.75, and (d10-d50) / d50 is 0.75 to 1.4. (ii) The difference between the log of the pore diameter d20 where the cumulative pore volume is 20% of the total pore volume and the log of the pore diameter d80 which is 80% σ = log (d20) -log (d80) is 0.39 or less. Yes, (iii) a ceramic honeycomb structure having a pore volume of more than 100 μm and a pore volume of 0.03 cm3 / g or less is disclosed. Even in the state before PM is deposited at the beginning of use (when the ceramic honeycomb filter is used from an unused state or when it is used again after being regenerated), it greatly affects the number of particles in the exhaust gas. It is described that the nano-sized PM can be effectively collected, the collection rate based on the number of PM particles is improved, and the pressure loss characteristic when the PM is collected is not deteriorated.

Special table 2009-542570 International Publication No. 2011/102487 International Publication No. 2015/04624 International Publication No. 2016/152709 International Publication No. 2016/152727

Due to the further tightening of emission regulations in recent years, NOx emission regulations have been strengthened, and studies are underway to apply catalysts that improve NOx purification performance. Oxidation catalysts, filters that collect PM, NOx catalysts that purify NOx, etc. are arranged in the exhaust system, but if you try to improve the purification performance of NOx, the pressure loss of the NOx catalyst will be higher than before. In some cases. However, since the pressure loss as an exhaust device needs to be maintained at the same level as the conventional one, it is necessary to reduce the pressure loss of the filter. As for the evaluation of the pressure loss of the ceramic honeycomb filter, for example, as described in Patent Document 4, the pressure loss after PM collection is such that the combustion soot having an average particle size of 0.11 μm is charged at a rate of 1.3 g / h and the filter is used. The evaluation is based on the differential pressure (pressure loss) between the inflow side and the outflow side when the amount of soot adhered per liter of volume is 2 g. However, in order to effectively collect nano-sized PM, which greatly affects the number of PM particles in the exhaust gas, and reduce the pressure loss of the ceramic honeycomb filter, it most affects the collection of nano-sized PM, and diesel. It is necessary to further reduce the pressure loss when the amount of soot adhered per liter of filter volume is 1 g (hereinafter, 1 g / L), which is the normal range of the engine and is the initial stage of PM collection.

In the ceramic honeycomb structures described in Patent Document 1, Patent Document 2, and Patent Document 3, although the pressure loss characteristics at the initial stage of PM collection are good, nano-sized PM that greatly affects the number of particles in the exhaust gas can be obtained. It may not be possible to collect effectively.
Further, in the ceramic honeycomb structures described in Patent Documents 4 and 5, nano-sized PM that greatly affects the number of particles in the exhaust gas can be obtained even in the state before the PM at the initial stage of use is deposited. Although the effect of effective collection is recognized, the pressure loss at the initial stage of PM collection is high, and improvement is desired.

Therefore, an object of the present invention is to reduce the pressure loss at the initial stage of PM collection (1 g / L) as compared with the conventional method, thereby effectively collecting nano-sized PM that greatly affects the number of PM particles in the exhaust gas. It is an object of the present invention to provide a ceramic honeycomb structure having a collection rate and a reduced pressure loss after PM collection.

In order to achieve the above object, the present inventor has focused on the pore distribution of the ceramic honeycomb structure of the present invention, and as a result of diligent studies, came up with the present invention. That is, the ceramic honeycomb structure of the present invention is a ceramic honeycomb structure having a large number of flow paths formed in the axial direction and partitioned by a porous partition wall, and the pore distribution of the partition wall is the total pore volume. : 0.70 to 0.80 cm ³ / g, pore volume of 1 μm or more: 0.68 to 0.78 cm ³ / g, pore volume of 2 μm or more: 0.65 to 0.75 cm ³ / g, pore volume of 5 μm or more: 0.58 to 0.68 cm ^{Pore volume of 3} / g, 10 μm or more: 0.42 to 0.56 cm ³ / g, Pore volume of 20 μm or more: 0.06 to 0.19 cm ³ / g, Pore volume of 30 μm or more: 0.03 to 0.10 cm ³ / g, 50 μm more pore volume: 0.02~0.05cm ³ / g, 100μm or more pore volume: 0.010~0.035cm ³ / g, 200μm or more pore volume: and wherein the 0.020cm is ³ / g or less.

In the ceramic honeycomb structure of the present invention, the difference between the logarithm of the pore diameter d20 in which the cumulative pore volume is 20% of the total pore volume and the logarithm of the pore diameter d80 in which the cumulative pore volume is 80% σ = log (d20) -log ( d80) is preferably 0.40 to 0.60.

In the ceramic honeycomb structure of the present invention, the coefficient of thermal expansion in the flow path direction between 40 and 800 ° C. is preferably 3 × 10 ^-7 / ° C. to 11 × 10 ^-7 / ° C.

According to the present invention, by lowering the pressure loss at the initial stage of PM collection (1 g / L) than before, PM collection that effectively collects nano-sized PM that greatly affects the number of PM particles in the exhaust gas. It is possible to provide a ceramic honeycomb structure having a rate and a reduced pressure loss after PM collection.

It is a front view which shows an example of a ceramic honeycomb filter schematically. It is sectional drawing parallel to the axial direction which shows an example of a ceramic honeycomb filter schematically. It is a cumulative pore volume curve which shows the relationship between the pore diameter and the cumulative pore volume of the partition wall of the ceramic honeycomb structure of Example 1 measured by the mercury intrusion method. It is a graph for demonstrating the method of obtaining d20 in the pore volume curve which showed the ratio with respect to the total pore volume in the cumulative pore volume curve shown in FIG.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The present invention is not limited to the following embodiments, and changes, modifications, and improvements can be made without departing from the scope of the invention.

[1] Ceramic Honeycomb Structure The ceramic honeycomb structure of the present invention is a ceramic honeycomb structure having a large number of flow paths formed in the axial direction and partitioned by a porous partition wall, and the pore size distribution of the partition wall is large. , Total pore volume: 0.70 to 0.80 cm ³ / g, pore volume of 1 μm or more: 0.68 to 0.78 cm ³ / g, pore volume of 2 μm or more: 0.65 to 0.75 cm ³ / g, pore volume of 5 μm or more : 0.58~0.68cm ³ / g, 10μm or more of the pore volume: 0.42~0.56cm ³ / g, 20μm or more of the pore volume: 0.06~0.19cm ³ / g, 30μm or more of the pore volume: 0.03~0.10cm ³ / g, 50 [mu] m or more pore volume: 0.02~0.05cm ³ / g, 100μm or more pore volume: 0.010~0.035cm ³ / g, 200μm or more pore volume: 0.020 cm is ³ / g or less

By having such a structure in the ceramic honeycomb structure, the pressure loss at the initial stage of PM collection (1 g / L) is reduced as compared with the conventional one while maintaining the strength of the ceramic honeycomb structure, so that PM in the exhaust gas is discharged. It is possible to have a ceramic honeycomb structure having a PM collection rate that effectively collects nano-sized PM, which greatly affects the number of particles, and a reduced pressure loss after PM collection.

(A) Pore distribution of partition wall (i) Total pore volume The total pore volume of the partition wall is 0.70 to 0.80 cm ³ / g. When the total pore volume is ^{less than 0.70 cm 3} / g, it becomes difficult to maintain a low pressure loss when PM is collected and accumulated, while when the total pore volume ^{exceeds 0.80 cm 3} / g, it becomes difficult to maintain. The nano-sized PM collection rate decreases. The lower limit of the total pore volume is preferably 0.71 cm ³ / g or more, more preferably 0.72 cm ³ / g or more, and the upper limit is preferably 0.79 cm ³ / g or less, still more preferably 0.78 cm ³ / g. It is as follows. The total pore volume of the partition wall is measured by the mercury press-fitting method described later.

(Ii) Pore volume of 1 μm or more
The pore volume of 1 μm or more is 0.68 to 0.78 cm ³ / g. When the pore volume of 1 μm or more is less than 0.68 cm ³ / g, it becomes difficult to reduce the pressure loss at the initial stage of PM collection (1 g / L). On the other hand, when the pore volume of 1 μm or more ^{exceeds 0.78 cm 3} / g, the nano-sized PM collection rate decreases. The lower limit of the pore volume of 1 μm or more is preferably 0.69 cm ³ / g or more, more preferably 0.70 cm ³ / g or more, and the upper limit is preferably 0.77 cm ³ / g or less, further preferably 0.76 cm ³ / g. It is as follows.

(Iii) Pore volume of 2 μm or more
The pore volume of 2 μm or more is 0.65 to 0.75 cm ³ / g. When the pore volume of 2 μm or more is ^{less than 0.65 cm 3} / g, it becomes difficult to reduce the pressure loss at the initial stage of PM collection (1 g / L). On the other hand, when the pore volume of 2 μm or more ^{exceeds 0.75 cm 3} / g, the nano-sized PM collection rate decreases. The lower limit of the above pore volume 2μm preferably 0.66 cm ³ / g or more, more preferably at 0.67 cm ³ / g or more, and the upper limit is preferably 0.74 cm ³ / g or less, more preferably 0.73 cm ³ / g It is as follows.

(Iv) Pore volume of 5 μm or more, 10 μm or more, 30 μm or more, 50 μm or more
More pore volume 5μm is 0.58~0.68cm ³ / g, more pore volume 10μm is 0.42~0.56cm ³ / g, more pore volume 30μm is 0.03~0.10cm ³ / g, 50μm or more pores The volume is 0.02-0.05 cm ³ / g. By having a pore volume of 5 μm or more, 10 μm or more, 30 μm or more, and 50 μm or more in such a range, the pressure loss at the initial stage of PM collection (1 g / L) is lower than before, and the number of PM particles in the exhaust gas is reduced. It has a PM collection rate that effectively collects nano-sized PM, which greatly affects the pressure loss after PM collection. Even when the NOx emission regulation is tightened and the pressure loss of the honeycomb structure on which the NOx catalyst is supported deteriorates as compared with the conventional one, the pressure loss as an exhaust device can be maintained at the same level as the conventional one. can. When the pore volume of 5 μm or more is ^{less than 0.58 cm 3} / g, when the pore volume of 10 μm or more is ^{less than 0.42 cm 3} / g, when the pore volume of 30 μm or more is ^{less than 0.03 cm 3} / g, 50 μm or more If the pore volume of is ^{less than 0.02 cm 3} / g, it becomes difficult to reduce the pressure loss at the initial stage of PM collection (1 g / L). On the other hand, when the pore volume of 5 μm or more ^{exceeds 0.68 cm 3} / g, when the pore volume of 10 μm or more exceeds 0.56 cm ³ / g, or when the pore volume of 30 μm or more exceeds 0.10 cm ³ / g, If the pore volume of 50 μm or more ^{exceeds 0.05 cm 3} / g, the nano-sized PM collection rate may decrease.
The lower limit of the pore volume of 5 μm or more is preferably 0.59 cm ³ / g or more, more preferably 0.60 cm ³ / g or more, and the upper limit is preferably 0.67 cm ³ / g or less, further preferably 0.66 cm ³ / g. It is as follows.
The lower limit of the pore volume of 10 μm or more is preferably 0.43 cm ³ / g or more, more preferably 0.44 cm ³ / g or more, and the upper limit is preferably 0.55 cm ³ / g or less, further preferably 0.54 cm ³ / g. It is as follows.
The lower limit of the pore volume of 30 μm or more is preferably 0.04 cm ³ / g or more, and the upper limit is preferably 0.09 cm ³ / g or less.
The lower limit of the pore volume of 50 μm or more is preferably 0.025 cm ³ / g or more, and the upper limit is preferably 0.045 cm ³ / g or less.

(V) Pore volume of 20 μm or more
The pore volume of 20 μm or more is 0.06 to 0.19 cm ³ / g. When the pore volume of 20 μm or more is ^{less than 0.06 cm 3} / g, it becomes difficult to reduce the pressure loss at the initial stage of PM collection (1 g / L). On the other hand, when the pore volume of 20 μm or more ^{exceeds 0.19 cm 3} / g, the nano-sized PM collection rate decreases. The lower limit of the above pore volume 20μm preferably 0.07 cm ³ / g or more, more preferably at 0.08 cm ³ / g or more, and the upper limit is preferably 0.18 cm ³ / g or less, more preferably 0.17 cm ³ / g It is as follows.

(Vi) Pore volume of 100 μm or more
The pore volume of 100 μm or more is 0.010 to 0.035 cm ³ / g. When the pore volume of 100 μm or more is ^{less than 0.010 cm 3} / g, it becomes difficult to reduce the pressure loss at the initial stage of PM collection (1 g / L). On the other hand, when the pore volume of 100 μm or more ^{exceeds 0.035 cm 3} / g, the nano-sized PM collection rate may decrease. The lower limit of the pore volume of 100 μm or more is preferably 0.015 cm ³ / g or more, and the upper limit is preferably 0.030 cm ³ / g or less.

(Vii) Pore volume of 200 μm or more
The pore volume of 200 μm or more is 0.020 cm ³ / g or less. If the pore volume of 200 μm or more ^{exceeds 0.020 cm 3} / g, the nano-sized PM collection rate may decrease. The upper limit of the pore volume of 200 μm or more is preferably 0.015 cm ³ / g or less.
(Viii) Difference between the logarithm of d20 and the logarithm of d80 σ
In the pore distribution curve of the partition wall measured by the mercury intrusion method, the logarithm of the pore diameter d20 (μm) where the cumulative pore volume is 20% of the total pore volume and the logarithm of the pore diameter d80 (μm) where the cumulative pore volume is 80%. The difference between σ = log (d20) and-log (d80) is 0.40 to 0.60. σ represents the slope at d20 and d80 in the pore distribution curve, and the larger the slope, that is, the larger the σ, the sharper the pore distribution, and while there are many pores of a specific size, the slope is When it is small, that is, when σ becomes small, the pore distribution becomes broad and pores of various sizes exist. When σ is less than 0.40, the presence of effective pores for nano-sized collection is reduced, and the nano-sized PM collection rate is reduced. On the other hand, when σ exceeds 0.60, the abundance of pores effective for reducing the pressure loss decreases, so that it becomes difficult to keep the initial pressure loss low at the start of use. The lower limit of σ is preferably 0.42 or more, and the upper limit is preferably 0.58 or less. In the present invention, the logarithm means a common logarithm having a base of 10. Here, the pore size distribution curve of the partition wall measured by the mercury intrusion method is, for example, a curve (cumulative pore volume curve) in which the cumulative pore volume is plotted against the pore diameter, as shown in FIG. It is expressed by integrating from the side with a large pore diameter to the side with a small pore diameter.

(Ix) Mercury injection method The cumulative pore volume measured by the mercury injection method can be measured using Autopore III 9410 manufactured by Micromeritics. This measurement is performed when a test piece (10 mm × 10 mm × 10 mm) cut out from a ceramic honeycomb structure is stored in a measurement cell, the inside of the cell is depressurized, and then mercury is introduced and pressurized. This is done by determining the volume of mercury pushed into the pores present in the piece. At this time, as the pressing force increases, mercury infiltrates into finer pores. Therefore, from the relationship between the pressing force and the volume of mercury pushed into the pores, the pore diameter and the cumulative pore volume (maximum). The relationship of the cumulative value of the pore volume from the pore diameter to the specific pore diameter) can be obtained. The infiltration of mercury is performed sequentially from the one having a large pore diameter to the one having a small pore diameter. ) Is plotted against the pore diameter, for example, as shown in FIG. 3, a graph showing the relationship between the pore diameter and the cumulative pore volume is obtained. In the present application, the pressure for introducing mercury is 0.5 psi (0.35 × 10 ^-3 kg / mm ² , equivalent to a pore diameter of about 362 μm), and the pressing force of mercury is 1800 psi (1.26 kg / mm ² , pore diameter of about 0.1 μm). The cumulative pore volume in (corresponding to) is defined as the total pore volume.

From the measurement results of the obtained mercury intrusion method, the total pore volume, the pore volume of 1 μm or more, the pore volume of 2 μm or more, the pore volume of 5 μm or more, the pore volume of 10 μm or more, the pore volume of 20 μm or more. , 30 μm or more pore volume, 50 μm or more pore volume, 100 μm or more pore volume, 200 μm or more pore volume, and the cumulative pore volume is 20% of the total pore volume. Calculate the difference σ = log (d20) -log (d80) between the logarithm and the logarithm of the pore diameter d80 which is 80%. The pore size distribution of the partition wall of the ceramic honeycomb structure of the present invention is the lower limit value at each pore volume described above in the graph of the pore diameter represented logarithmically on the horizontal axis and the cumulative pore volume represented linearly on the vertical axis. It is characterized in that it is in the area between the range connecting the upper limit values with a straight line and the range connecting the upper limit values with a straight line.
(B) Thermal expansion coefficient The ceramic honeycomb structure preferably has a thermal expansion coefficient of 3 × 10 ^-7 / ° C to 11 × 10 ^-7 / ° C in the flow path direction between 40 and 800 ° C. Since the ceramic honeycomb structure having such a coefficient of thermal expansion has high thermal shock resistance, it can sufficiently withstand practical use as a ceramic honeycomb filter for removing fine particles contained in the exhaust gas of a diesel engine. .. The coefficient of thermal expansion is preferably 4 × 10 ^-7 / ° C to 11 × 10 ^-7 / ° C, more preferably 5 × 10 ^-7 / ° C to 10 × 10 ^-7 / ° C.

(C) Partition structure The ceramic honeycomb structure preferably has an average partition thickness of 6 to 14 mil (0.152 to 0.356 mm) and an average cell density of 150 to 300 cpsi (23.3 to 46.5 cells / cm ² ). By having such a partition structure, the pressure loss can be kept low at the start of use, the PM collection rate based on the number of particles can be improved, and the pressure loss at the initial stage of PM collection (1 g / L) can be improved. Is reduced and the pressure drop characteristics when PM is collected and accumulated are improved. If the average bulkhead thickness is less than 6 mils, the bulkhead strength will be reduced, while if it exceeds 14 mils, it will be difficult to maintain low pressure drop. It is preferably 7 to 13 mil (0.178 to 0.330 mm), more preferably 8 to 12 mil (0.203 to 0.305 mm). If the average cell density is less than 150 cpsi, the strength of the bulkhead will be reduced, while if it exceeds 300 cpsi, it will be difficult to maintain low pressure drop. The flow path shape in the cross section orthogonal to the flow path direction of the ceramic honeycomb structure may be any of polygons such as quadrangles, hexagons, and octagons, circles, ellipses, and the like, and the inflow side end face and the outflow side end face are large. It may be an asymmetrical shape having a different sheath shape (for example, an octagon on the inflow side and a quadrangle on the outflow side).

(D) Material of partition wall As the material of the partition wall, since the purpose of the ceramic honeycomb structure is a filter for purifying the exhaust gas discharged from the diesel engine, heat-resistant ceramics, that is, alumina, mullite, and cordy. Ceramics having mullite, silicon carbide, silicon nitride, zirconia, aluminum titanate, lithium aluminum silicate or the like as main crystals are preferable. Of these, those containing cordierite, which has excellent thermal shock resistance and low thermal expansion, as the main crystal are preferable. When the main crystal phase is cordierite, it may contain other crystal phases such as spinel, mullite, and sapphirine, and may further contain a glass component.

[2] Ceramic Honeycomb Filter The ceramic honeycomb filter is formed by alternately sealing the exhaust gas inflow side or the exhaust gas outflow side of the flow path of the ceramic honeycomb structure of the present invention. By using the ceramic honeycomb structure of the present invention, it is possible to maintain a low pressure loss and improve the PM collection rate based on the number of particles at the start of use, and further, PM is collected and accumulated. A ceramic honeycomb filter having improved pressure loss characteristics can be obtained. Here, the sealing formed on the flow path may be formed on the end face portion of the exhaust gas inflow side or the exhaust gas outflow side of the flow path, and enters the inside of the flow path from the inflow side end face or the outflow side end face. It may be formed at a position.

[3] Method for Manufacturing a Ceramic Honeycomb Structure The method for manufacturing a ceramic honeycomb structure of the present invention will be described, but the present invention is not limited to the embodiments described below, and is not deviating from the gist of the present invention. It should be understood that, based on the ordinary knowledge of those skilled in the art, the following embodiments with appropriate changes, improvements, etc. are also included in the scope of the present invention.

A method for producing a ceramic honeycomb structure, which comprises a step of extruding a clay containing a ceramic raw material powder and a pore-forming material into a predetermined molded body, and drying and firing the molded body, wherein the ceramic honeycomb structure is contained in the clay. The ratio of the pore-forming material is 2 to 15 parts by mass externally to 100 parts by mass of the ceramic raw material powder, and the ceramic raw material powder is 15 to 22% by mass of silica and 27 to 43% by mass of talc. Containing 15 to 30% by mass of alumina and 1 to 13% by mass of kaolin, the silica is a particle having a median diameter D50 of 5 μm or more and less than 13 μm, D10 of 1 to 4 μm, D90 of 7 to 25 μm, and 100 μm or more. The proportion of particles with a diameter is 0.1% by mass or less, and the particle size distribution deviation is SD1 [However, SD1 = log (D80) -log (D20), and D20 is the particle size in the cumulative volume corresponding to 20% of the total volume. D80 is the particle size in the cumulative volume corresponding to 80% of the total volume, and D20 <D80. ] Is 0.40 to 0.65, the talc has a median diameter D50 of 5 to 15 μm, the alumina has a median diameter D50 of 2 to 7 μm, and the pore-forming material is a hollow having an inorganic powder on the surface. In the curve showing the relationship between the particle size and the cumulative volume, the median diameter D50 is 15 to 35 μm, and the particle size D5 at the cumulative volume corresponding to 5% of the total volume is 2 to 8 μm, 10%. The particle size D10 in the corresponding cumulative volume is 4 to 14 μm, the particle size D90 in the cumulative volume corresponding to 90% is 30 to 50 μm, and the particle size distribution deviation SD2 [However, SD2 = log (D80) -log (D20) D20 is the particle size in the cumulative volume corresponding to 20% of the total volume, and D80 is the particle size in the cumulative volume corresponding to 80% of the total volume, and D20 <D80. ] Is 0.40 to 0.55.

By such a method, the pore size distribution of the partition wall measured by the mercury intrusion method is: total pore volume: 0.70 to 0.80 cm ³ / g, pore volume of 1 μm or more: 0.68 to 0.78 cm ³ / g, 2 μm or more. pore volume: 0.65~0.75cm ³ / g, 5μm or more pore volume: 0.58~0.68cm ³ / g, 10μm or more pore volume: 0.42~0.56cm ³ / g, 20μm or more pore volume: 0.06~0.19cm ³ / g, 30μm or more pore volume: 0.03~0.10cm ³ / g, 50μm or more pore volume: 0.02~0.05cm ³ / g, 100μm or more pore volume: 0.01~0.035cm ³ A ceramic honeycomb structure having a pore volume of / g and 200 μm or more: 0.02 cm ³ / g or less can be obtained.

The pores formed in the ceramics are composed of pores formed by melting the ceramic raw material powder and the inorganic powder on the surface of the pore-forming material in the firing process, and pores formed by burning the pore-forming material. Therefore, by setting the median diameter and particle size distribution of the ceramic raw material powder and the pore-forming material within the above-mentioned ranges, it is possible to control the pores generated when the ceramic is fired.

In the production method of the present invention, by using hollow resin particles having an inorganic powder on the surface as the pore-forming material, the resin particles are burned when the molded body containing the ceramic raw material powder and the pore-forming material is fired. As a result, the ceramic raw material powder and the inorganic powder on the surface of the pore-forming material are fired to form pores. In the present invention, by using hollow resin particles that generate less heat due to combustion than solid resin particles, firing cracks are less likely to occur in the process of firing the molded product. At this time, since the pores generated by firing the ceramic raw material powder and the pores formed by the resin particles communicate with each other, the communication of the pores from the partition surface to the inside is improved, and the measurement is performed by the mercury intrusion method. The pore distribution of the formed partition wall can be within the above range.

In this way, by forming the pores generated by firing the ceramic raw material powder and the pores formed from the pore-forming material into a predetermined pore distribution with good communication, the nano-sized PM collection rate and PM The pressure loss at the initial stage of collection can be further reduced, and as a result, a ceramic honeycomb structure having improved pressure loss after PM collection can be obtained.

(1) Ceramic raw material powder The ceramic raw material powder contains 15 to 22% by mass of silica, 27 to 43% by mass of talc, 15 to 30% by mass of alumina, and 1 to 13% by mass of kaolin. The ceramic raw material powder is preferably a cordierite raw material. The main crystal of the raw material for making cordierite is cordierite (SiO _{2 with a chemical composition of 42 to 56% by mass, Al 2} O _{3 with} 30 to 45% by mass, and MgO with 12 to 16% by mass). As described above, each raw material powder having a silica source component, an alumina source component and a magnesia source component is blended, and is composed of, for example, silica, talc, alumina, kaolin, aluminum hydroxide and the like. The pores formed in ceramics having cordierite as the main crystal include pores formed by firing silica and talc as ceramic raw materials, and pores formed by melting inorganic powder on the surface of the pore-forming material. This is due to the pores generated by burning the pore-forming material. Therefore, by adjusting the particle size and particle size distribution of the ceramic raw material powder such as silica and talc together with the above-mentioned pore-forming material, it is possible to control the pores generated when the cordierite ceramics are fired. Among them, silica and the pore-forming material occupy most of the formed pores, and therefore contribute greatly to the pore structure.

(A) Silica It is known that silica exists stably up to a high temperature, and at 1300 ° C. or higher, the melting point is lowered by a reaction with other raw materials and diffuses into a liquid phase to form pores. Therefore, when 15 to 22% by mass of silica is contained, a desired amount of pores can be obtained. If it is less than 15% by mass, the number of pores formed in the partition wall is reduced, so that a low pressure loss when PM is collected and accumulated may not be obtained. On the other hand, if silica is contained in excess of 22% by weight, other silica source components, kaolin and / or talc, must be reduced in order to maintain the main crystal in cordierite, resulting in kaolin. The effect of low thermal expansion (effect obtained by orienting kaolin during extrusion molding) is reduced, and the thermal shock resistance is reduced. The silica content is preferably 17-21% by mass.

Silica has a median diameter D50 of 5 to 13 μm, and in the curve showing the relationship between the particle size and the cumulative volume, the particle size D10 at the cumulative volume corresponding to 10% of the total volume is 1 to 4 μm, and 90% of the total volume. The particle size D90 in the cumulative volume corresponding to is 7 to 25 μm, the proportion of particles with a particle size of 100 μm or more is 0.1% by mass or less, and the particle size distribution deviation SD1 [However, SD1 = log (D80) -log (D20) D20 is the particle size in the cumulative volume corresponding to 20% of the total volume, and D80 is the particle size in the cumulative volume corresponding to 80% of the total volume, and D20 <D80. ] Has a particle distribution of 0.40 to 0.65. Since silica greatly contributes to the pore structure formed when the cordierite ceramics are fired, silica having such a particle distribution or talc described later can be used in combination with the pore-forming material. , specific pore distribution, in particular, 5 [mu] m or more pore volume 0.58~0.68cm ³ / g, 10μm or more pore volume 0.42~0.56cm ³ / g, or more of the pore volume 30 [mu] m 0.03～0.10Cm ^{The pore volume of 3} / g, 50 μm or more is in ^{the range of 0.02 to 0.05 cm 3} / g, and the pressure at the initial stage of PM collection while the nano-sized PM is effectively collected and the PM collection rate is maintained. The ceramic honeycomb structure of the present invention having further improved loss characteristics can be obtained.

When the median diameter D50 of silica is less than 5 μm, the proportion of micropores in the pores formed in the partition wall increases, which causes an increase in pressure loss when PM is collected and accumulated. On the other hand, when it exceeds 13 μm, the number of coarse pores increases and the nano-sized PM collection rate decreases. The lower limit of the silica media diameter D50 is preferably 5.5 μm or more, more preferably 6 μm or more, and the upper limit is preferably 12 μm or less, further preferably 11 μm or less.

If the D10 of silica is less than 1 μm, the proportion of micropores formed in the partition wall that deteriorates the pressure loss characteristics increases, which is not preferable. On the other hand, if it exceeds 4 μm, it may be difficult to effectively collect nano-sized PM. The lower limit of D10 of silica is preferably 1.5 μm or more, more preferably 2.0 μm or more, and the upper limit is preferably 3.5 μm or less, further preferably 3.0 μm or less.

If the D90 of silica is less than 7 μm, the proportion of micropores formed in the partition wall that deteriorates the pressure loss characteristics increases, which is not preferable. On the other hand, if it exceeds 25 μm, the proportion of coarse pores that reduce the nano-sized PM collection rate increases, which is not preferable. The lower limit of D90 of silica is preferably 8 μm or more, more preferably 9 μm or more, the upper limit is preferably 24 μm or less, preferably 23 μm or less, and the lower limit is preferably 8 μm or more, further preferably 9 μm or more.

When the proportion of silica having a particle size of 100 μm or more exceeds 0.1% by mass, the number of coarse pores increases and the nano-sized PM collection rate decreases. The proportion of silica having a particle size of 100 μm or more is preferably 0.05% or less.

If the particle size distribution deviation SD1 exceeds 0.65, the proportion of coarse pores that reduce the nano-sized PM collection rate increases, which is not preferable. On the other hand, if it is less than 0.40, the proportion of micropores in the pores formed in the partition wall increases, which causes an increase in pressure loss when PM is collected and accumulated. The upper limit is preferably 0.64 or less, more preferably 0.63 or less, and the lower limit is preferably 0.42 or more, further preferably 0.44 or more.

The sphericity of the silica is preferably 0.5 or more. When the sphericity of silica is less than 0.5, the number of pores having acute-angled portions, which are likely to be the starting points of fracture, may increase and the strength of the honeycomb structure may decrease, which is not preferable. The sphericity of silica is preferably 0.6 or more, and more preferably 0.7 or more. The sphericity of a silica particle is a value obtained by dividing the projected area of the silica particle by the area of a circle whose diameter is the maximum value of a straight line connecting two points on the outer circumference of the particle through the center of gravity of the silica particle. It can be obtained with an image analyzer.

As the silica, a crystalline one or an amorphous one can be used, but an amorphous one is preferable from the viewpoint of adjusting the particle size distribution. Amorphous silica can be obtained by pulverizing an ingot produced by melting high-purity natural silica stone at a high temperature. _{Silica may contain Na 2} O, K ₂ O, and Ca O as impurities, but the total content of the impurities is preferably 0.1% or less in order to prevent the coefficient of thermal expansion from becoming large.

Silica with high sphericity is obtained by finely pulverizing high-purity natural silica stone and spraying it into a high-temperature flame. Amorphous silica with high sphericity can be obtained by simultaneously melting and spheroidizing silica particles by spraying into a high-temperature flame. Further, it is preferable to adjust the particle size of the spherical silica by a method such as classification.

(B) Kaolin Kaolin contains 1 to 13% by mass. When the content of kaolin is less than 1% by mass, the effect of low thermal expansion obtained by orienting kaolin during extrusion molding is reduced, and the coefficient of thermal expansion of the ceramic honeycomb structure is increased. On the other hand, if kaolin is contained in excess of 13% by mass, other silica source components, silica and / or talc, must be reduced in order to maintain the main crystal in cordierite, resulting in a ceramic honeycomb. It may be difficult to adjust the pore distribution of the partition walls of the structure to the scope of the present invention. The kaolin content is preferably 4-8% by mass.

The plate-like crystal of kaolin undergoes a rectifying action when passing through a mold during extrusion molding, and the c-axis of the crystal is oriented perpendicularly to the partition surface of the honeycomb structure. In the firing process of cordierite, the cordierite crystal grows on the c-axis, which has a negative thermal expansion in the direction perpendicular to the c-axis of the kaolin crystal, and the coefficient of thermal expansion of the honeycomb structure can be reduced. Therefore, the shape of kaolin has a great influence on the orientation of kaolin. The cleavage index of kaolin, which is an index that quantitatively indicates the shape of kaolin, is preferably 0.80 or more, and more preferably 0.85 or more. The cleavage index of kaolin was obtained by press-filling a container with a certain amount of kaolin and performing X-ray diffraction measurement of the pressed surface, as described in Japanese Patent Application Laid-Open No. 2006-265034. _{From the peak intensities I (200)} , I ₍₀₂₀₎ and I _{(002) of} the (020) and (002) planes, the following equation:
Cleavage index = I ₍₀₀₂₎ / [I ₍₂₀₀₎ + I ₍₀₂₀₎ + I ₍₀₀₂₎ ]
Can be obtained by. It can be said that the larger the cleavage coefficient, the better the orientation of the kaolin particles.

(C) Talc Talc is contained in an amount of 27 to 43% by mass. For talc, the median diameter D50 is 5 to 15 μm, and the cumulative volume corresponding to 10% of the total volume in the curve showing the relationship between the particle size and the cumulative volume (the cumulative value of the particle volume below a specific particle size). A talc having a particle size D10 of 1 to 8 μm and a particle size D90 of 20 to 40 μm in a cumulative volume corresponding to 90% of the total volume is used. Talc is a compound containing Mg O _{and SiO 2} as main components, and is known to react with the _{surrounding Al 2 O 3 components and melt to form pores during the firing process.} Therefore, _{by blending talc having a small particle size together with the Al 2} O ₃ source raw material, a large number of small-diameter pores can be dispersed in the partition wall, and the communication of the pores in the partition wall can be improved. When the median diameter D50 of talc is less than 5 μm, the communication of pores is low, and the pressure drop characteristic when PM is collected and accumulated is lowered. On the other hand, when the median diameter D50 of talc exceeds 15 μm, the number of coarse pores increases and the nano-sized PM collection rate decreases. The median diameter D50 of talc is preferably 6-14 μm, more preferably 8-13 μm.

Here, when talc is used as the inorganic powder on the surface of the resin particles of the cordierite, the content of talc to be mixed in the cordierite-forming raw material is determined in consideration of the talc content of the cordierite. Adjust the amount of talc added to the lightening raw material.

The upper limit of D10 for talc is preferably 7 μm or less, more preferably 6 μm or less. The D90 of talc is preferably 22 to 38 μm, more preferably 24 to 36 μm.

Talc is preferably plate-like particles from the viewpoint of reducing the coefficient of thermal expansion of the ceramic honeycomb structure in which the main component of the crystal phase is cordierite. The view factor indicating the flatness of talc is preferably 0.5 or more, more preferably 0.6 or more, and most preferably 0.7 or more. As described in US Pat. No. 5,141,686, the view factors are the diffraction intensity Ix of the (004) plane and the diffraction intensity of the (020) plane obtained by X-ray diffraction measurement of the talc of the plate-like particles. From Iy:
View factor = Ix / (Ix + 2Iy)
Can be obtained by. The larger the view factor, the higher the flatness of talc.

Talc may contain Fe ₂ O ₃ , Ca _{O, Na 2} O, K ₂ O and the like as impurities. The content of Fe ₂ O ₃ is preferably 0.5 to 2.5% by mass in the raw material of the magnesia source in order to obtain a desired particle size distribution, _{and the content of Na 2} O, K ₂ O and Ca O is thermally expanded. From the viewpoint of lowering the coefficient, the total amount is preferably 0.5% by mass or less.

(D) Alumina Alumina is contained in an amount of 15 to 30% by mass. As the alumina, the median diameter D50 is 2 to 7 μm, and in the curve showing the relationship between the particle size and the cumulative volume, the particle size D90 at the cumulative volume corresponding to 90% of the total volume is 5 to 20 μm, 25 μm. Alumina having a particle size of 0.5% by mass or less is used. By blending alumina having such a median diameter and particle size distribution, a large number of small-diameter pores can be dispersed in the partition wall, so that the communication of the pores in the partition wall can be improved. It contributes to the formation of the pore distribution of the ceramic honeycomb structure of the present invention. The lower limit of the median diameter D50 of alumina is preferably 2.5 μm or more, more preferably 3.0 μm or more, and the upper limit is preferably 6.5 μm or less, further preferably 6 μm or less. The lower limit of D90 is preferably 6 μm or more, more preferably 7 μm or more, and the upper limit is preferably 19 μm or less, further preferably 18 μm or less. The proportion of particles having a particle size of 25 μm or more is preferably 0.3% by mass or less.
As a raw material having an alumina source component, it is preferable to use aluminum hydroxide in addition to alumina. The total content of the impurities Na ₂ O, K ₂ O and Ca O in alumina and aluminum hydroxide is preferably 0.5% by mass or less, more preferably 0.3% by mass or less, and most preferably 0.1% by mass or less. ..

(2) Pore-making material
(a) Structure The pore-forming material used in the present invention consists of hollow resin particles having inorganic powder on the surface, and the amount of the pore-forming material added is 2 to 15 parts by mass externally with respect to 100 parts by mass of the ceramic raw material powder. Is. If the amount of the pore-forming material added is out of this range, it becomes difficult to obtain a partition wall having the pore structure. When the amount of the pore-forming material added is less than 2% by mass, ^{it becomes difficult to obtain a partition wall having a total pore volume of 0.70 cm 3} / g or more, so that the pressure loss characteristic when PM is collected and accumulated deteriorates. do. If the amount of the pore-forming material added exceeds 15% by mass, the total pore volume of the partition wall may exceed 0.80 cm ³ / g, which reduces the nano-sized PM collection rate and the strength of the ceramic honeycomb structure. May decrease. The lower limit of the amount of the pore-forming material added is preferably 2.5 parts by mass or more, more preferably 3.0 parts by mass or more, and the upper limit is preferably 14 parts by mass or less, still more preferably 13 parts by mass or less, and even more preferably. It is 12 parts by mass or less, most preferably 11 parts by mass or less.

The median diameter D50 of the pore-forming material is 15 to 35 μm. If the median diameter D50 is less than 15 μm, the low pressure loss when PM is collected and accumulated cannot be maintained. When the median diameter D50 exceeds 35 μm, the pores formed become coarse, so that the nano-sized PM collection rate may decrease and the strength of the ceramic honeycomb structure may decrease. The lower limit of the median diameter D50 of the pore-forming material is preferably 18 μm or more, more preferably 20 μm or more, and the upper limit is preferably 32 μm or less, further preferably 30 μm or less.

The pore-forming material has a particle diameter D5 at a cumulative volume corresponding to 5% of the total volume in a curve showing the relationship between the particle diameter and the cumulative volume (value obtained by accumulating the particle volumes below a specific particle diameter). 2 to 8 μm, particle size D10 in cumulative volume corresponding to 10% of total volume is 4 to 14 μm, particle size D90 in cumulative volume corresponding to 90% of total volume is 30 to 50 μm, particle size distribution deviation SD2 [However , SD2 = log (D80) -log (D20), D20 is the particle size in the cumulative volume corresponding to 20% of the total volume, and D80 is the particle size in the cumulative volume corresponding to 80% of the total volume. D20 <D80. ] Is 0.40 to 0.55. Since the pore-forming material greatly contributes to the pore structure formed when the cordierite ceramics are fired, the pore-forming material has such a particle size distribution and is a grain of the ceramic raw material powder described later. By adjusting the diameter and particle size distribution, it becomes easy to obtain a partition having the pore structure. The lower limit of D5 is preferably 2.5 μm or more, more preferably 3.0 μm or more, and the upper limit is preferably 7.5 μm or less, further preferably 7.0 μm or less. The lower limit of D10 is 5 μm or more, more preferably 6 μm or more, and the upper limit is preferably 13 μm or less, more preferably 12 μm or less. The lower limit of D90 is preferably 32 μm or more, more preferably 34 μm or more, and the upper limit is preferably 48 μm or less, further preferably 46 μm or less. The lower limit of the particle size distribution deviation SD2 is preferably 0.42 or more, more preferably 0.44 or more, and the upper limit is preferably 0.53 or less, further preferably 0.50 or less. In addition, D5 <D10 <D20 <D50 <D80 <D90. The particle size of the pore-forming material can be measured using a Microtrack particle size distribution measuring device (MT3000) manufactured by Nikkiso Co., Ltd.

The sphericity of the pore-forming material is preferably 0.5 or more. When the sphericity of the pore-forming material is less than 0.5, the number of pores having acute-angled portions, which are likely to be the starting points of fracture, may increase and the strength of the honeycomb structure may decrease, which is not preferable. The sphericity of the pore-forming material is preferably 0.7 or more, and more preferably 0.8 or more. The sphericity of the pore-forming material is the value obtained by dividing the projected area of the pore-forming material by the area of a circle whose diameter is the maximum value of a straight line that passes through the center of gravity of the pore-forming material and connects two points on the outer circumference of the particle. , Can be obtained from an electron micrograph with an image analyzer.

(b) Resin particles As the hollow resin particles, foamed resin particles are preferable. As the resin used as the pore-forming material, (poly) methyl methacrylate, polybutyl methacrylate, polyacrylic acid ester, polystyrene, polyacrylic ester, polyethylene, polyethylene terephthalate, methyl methacrylate / acrylonitrile copolymer and the like are suitable. Hollow resin particles have an outer shell thickness of 0.1 to 3 μm, contain a gas such as a hydrocarbon, contain 70 to 95% of water on the surface of the resin particles, and have a true specific gravity of 0.01 to 0.05. It is preferable to use one.

(c) Inorganic powder The inorganic powder on the surface of the hollow resin is at least one selected from the group consisting of talc, silica, kaolin, cordierite, alumina, aluminum hydroxide, calcium carbonate, and titanium oxide. Is preferable. Above all, when the ceramic honeycomb structure uses low thermal expansion cordierite, which has excellent thermal shock resistance, as the main crystal phase, the inorganic powders include talc, silica, kaolin, alumina, and aluminum hydroxide, which are raw materials for cordierite formation. Or, cordierite is preferable, and talc is most preferable. Therefore, it is preferable to use a talc-coated hollow resin in which the inorganic powder is talc as the pore-forming material.

The inorganic powder on the surface of the hollow resin has a median diameter D50 of 0.2 to 16 μm because pores are formed with good communication when the ceramic raw material and the inorganic powder are fired. It is preferably 0.4 to 14 μm, more preferably 0.6 to 12 μm.

The median diameter D50 (d) of the inorganic powder is preferably selected so that the d / D is 0.5 or less with respect to the median diameter D50 (D) of the resin particles. By setting the d / D in such a range, the inorganic powder can be satisfactorily adhered to the surface of the resin particles.

(3) Manufacturing method For the ceramic honeycomb structure, a binder is added to the ceramic raw material powder and the pore-forming material and mixed in a dry manner, and then water and, if necessary, additives such as a dispersant and a surfactant are added. The plastic clay obtained by kneading is extruded from a known extrusion die for forming a honeycomb structure by an extrusion molding method such as a plunger type or a screw type. It is manufactured by forming a molded body having a honeycomb structure, drying the molded body, processing the end face and the outer periphery as necessary, and firing the molded body.

Firing is performed using a continuous furnace or a batch furnace while adjusting the rate of temperature rise and cooling. When the ceramic raw material is a cordierite raw material, it is kept at 1350 to 1450 ° C. for 1 to 50 hours, and after sufficient cordierite main crystals are formed, it is cooled to room temperature. The temperature rise rate is a temperature range in which the binder decomposes (for example, when a large ceramic honeycomb structure having an outer diameter of 150 mm or more and a total length of 150 mm or more is manufactured, so that the molded body does not crack during the firing process). It is preferably 0.2 to 10 ° C./hr in the range of 150 to 350 ° C., and 5 to 20 ° C./hr in the temperature range in which the coordinating reaction proceeds (for example, 1150 to 1400 ° C.). Cooling is preferably performed at a rate of 20-40 ° C / h, especially in the range of 1400-1300 ° C.

The obtained honeycomb structure can be made into a ceramic honeycomb filter by sealing the end of a desired flow path by a known method. In addition, this seal sealing part may be formed before firing.

Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples.

(Examples 1 and 2, Comparative Examples 1 and 2)
Silica, talc, alumina, aluminum hydroxide and kaolin having the particle shapes (particle size, particle size distribution, etc.) shown in Tables 1 to 5 are blended in the amount shown in Table 8, and the chemical composition is cordierite after firing. A cordierite raw material powder was obtained. The amount of talc added in Examples 1 and 2 and Comparative Example 2 was adjusted in consideration of the talc content of the pore-forming material (talc-coated hollow resin) having inorganic powder (talc) on the surface shown in Tables 6 and 7. ..

To this cordierite raw material powder, the pore-forming materials having the particle size distribution and true specific gravity shown in Tables 6 and 7 were added in the amounts shown in Table 8, methyl cellulose was added and mixed, and then water was added and kneaded. , A plastic ceramic cordierite was made. The sphericity of the pore-forming material particles is a circle whose diameter is the maximum value of the projected area A1 obtained from the image of the particles taken by the electron microscope and the straight line connecting the two points on the outer circumference of the particles through the center of gravity. It is a value calculated by the formula: A1 / A2 from the area A2 of, and is shown as an average value for 20 particles.

The particle size and particle size distribution of silica, talc, alumina, aluminum hydroxide, kaolin and pore-forming material were measured using a Microtrack particle size distribution measuring device (MT3000) manufactured by Nikkiso Co., Ltd. The ratio of diameter 25 μm or more, the ratio of 100 μm or more, D90, D80, D20, D10, etc. were determined.

The obtained clay was extruded with a mold to prepare a molded body having a honeycomb structure.
After the molded product is dried, the peripheral part is removed and processed, and the schedule is 210 hours in a firing furnace (10 ° C / h for room temperature to 150 ° C, 2 ° C / hr for 150 to 350 ° C, 20 ° C / hr for 350 to 1150 ° C). h and 1150 to 1410 ° C are heated at an average rate of 15 ° C / hr, the maximum temperature is 1410 ° C and 25 hr is maintained, and 1400 to 1300 ° C is 30 ° C / hr, and 1300 to 100 ° C is an average of 80 ° C / hr. (Cooling at speed) was fired. The outer circumference of the fired ceramic honeycomb is coated with an outer skin material composed of amorphous silica and colloidal silica and dried. The outer diameter is 266.7 mm, the total length is 304.8 mm, the partition wall thickness is 12 mil (0.30 mm), and the cell density is 260 cpsi ( Ceramic honeycomb structures of Examples 1 and 2 and Comparative Examples 1 and 2 having 40.3 cells / cm ^{2) were obtained.}

The flow path ends of these ceramic honeycomb structures are filled with a sealant slurry made of a cordierite-forming raw material so as to be alternately sealed, and then the sealant slurry is dried and at 1400 ° C. Each of the Codylite ceramic honeycomb filters of Examples and Comparative Examples was produced. The length of the sealant after firing was in the range of 7-10 mm. Two identical ceramic honeycomb filters were made.

Using one of the obtained ceramic honeycomb filters of Examples 1 and 2 and Comparative Examples 1 and 2, the pore distribution was measured by the mercury intrusion method and the coefficient of thermal expansion was measured by the following method.
(a) Measurement of pore distribution For the measurement of pore distribution by the mercury intrusion method, a test piece (10 mm × 10 mm × 10 mm) cut out from a ceramic honeycomb filter is stored in the measurement cell of Autopore III manufactured by Micromeritics, and the cell is used. After depressurizing the inside, mercury was introduced and pressurized, and the relationship between the pressure at the time of pressurization and the volume of mercury pushed into the pores existing in the test piece was obtained. The pressure is converted into the pore diameter, and the cumulative pore volume (corresponding to the volume of mercury) integrated from the larger pore diameter side to the smaller pore diameter side is plotted against the pore diameter, and as shown in FIG. A graph showing the relationship between the pore size and the cumulative pore volume was obtained. The pressure for introducing mercury was 0.5 psi (0.35 × 10 ^-3 kg / mm ² ), and the values of contact angle = 130 ° and surface tension = 484 dyne / cm were used as the constants when calculating the pore diameter from the pressure. .. Then, the cumulative pore volume at a mercury pressing pressure of 1800 psi (1.26 kg / mm ² , corresponding to a pore diameter of about 0.1 μm) was defined as the total pore volume.

From the measurement results of the obtained mercury intrusion method, the total pore volume, the pore volume of 1 μm or more, the pore volume of 2 μm or more, the pore volume of 5 μm or more, the pore volume of 10 μm or more, the pore volume of 20 μm or more. , 30 μm or more pore volume, 50 μm or more pore volume, 100 μm or more pore volume, 200 μm or more pore volume, and the cumulative pore volume is 20% of the total pore volume. The difference σ = log (d20) -log (d80) between the logarithm and the logarithm of the pore diameter d80 which is 80% was calculated. Here, the values of the pore diameters d20 and d80 were obtained by interpolating the two measurement points before and after the closest to each pore diameter among the measurement points obtained by the measurement by the mercury intrusion method. For example, in the case of d20, as shown in FIG. 4, among the measurement points obtained by the mercury intrusion method, before and after the value of the pore diameter at which the cumulative pore volume is 20% of the total pore volume is the closest. The two measurement points A and B were connected by a straight line, and the pore diameter at the point where the cumulative pore volume was 20% of the total pore volume on the straight line was defined as d20. These results are shown in Tables 9 and 10.

(b) Measurement of coefficient of thermal expansion The coefficient of thermal expansion is obtained by cutting out a test piece having a cross-sectional shape of 4.5 mm × 4.5 mm and a length of 50 mm so that the longitudinal direction almost coincides with the flow path direction. Increase in length in the total length when heated from room temperature to 800 ° C at a heating rate of 10 ° C / min while applying a constant load of 20 g using TMA, ThermoPlus manufactured by Rigaku Co., Ltd., compression load method / differential expansion method) The amount was measured and determined as the average coefficient of thermal expansion between 40 and 800 ° C. The results are shown in Table 10.

(c) Initial pressure loss The initial pressure loss is expressed by the differential pressure (pressure loss) between the inflow side and the outflow side when air is sent to the ceramic honeycomb filter fixed to the pressure loss test stand at a flow rate of 10 Nm ^{3 / min.} Pressure loss,
When it exceeds 1.0kPa (×),
When it exceeds 0.8 kPa and is 1.0 kPa or less (○),
When it exceeds 0.6 kPa and is 0.8 kPa or less (◎), and
In case of 0.6kPa or less (◎)
The initial pressure drop was evaluated as.

(d) PM collection initial stage (1 g / L) pressure loss
For the initial PM collection (1 g / L) pressure loss, ^{combustion soot with an air flow rate of 10 Nm 3} / min and an average particle size of 0.11 μm is injected into a ceramic honeycomb filter fixed to the pressure loss test stand at a rate of 1.3 g / h. However, it was expressed as the differential pressure (pressure loss) between the inflow side and the outflow side when the amount of soot attached per liter of filter volume was 1 g. Pressure loss,
When it exceeds 1.3kPa (×),
When it exceeds 1.0 kPa and is 1.3 kPa or less (△),
When it exceeds 0.8 kPa and is 1.0 kPa or less (○), and
In case of 0.8kPa or less (◎)
The soot collection pressure loss was evaluated as.

(e) PM collection rate based on the number of particles after the start of collection The PM collection rate based on the number of particles after the start of collection is the air flow rate of 10 Nm ³ / on a ceramic honeycomb filter fixed to the pressure loss test stand. At min, while adding combustion soot with an average particle size of 0.11 μm at a rate of 1.3 g / h, the number of combustion soot particles flowing into the honeycomb filter and the number of combustion soot particles flowing out of the honeycomb filter are measured every minute. Measured using SMPS (Scanning Mobility Particle Sizer) (TIS model 3936), the number of particles of combustion soot flowing into the honeycomb filter in 1 minute from 40 minutes to 41 minutes after the start of injection, and from the honeycomb filter From the number of particles of the outflowing combustion soot Nout, it was calculated by the formula: (Nin-Nout) / Nin. PM collection rate,
98% or more (◎),
When 96% or more and less than 98% (○),
When 95% or more and less than 96% (△), and
If it is less than 95% (×)
The PM collection rate was evaluated as.

From Table 11, the ceramic honeycomb filters of the present invention of Examples 1 and 2 have a PM collection rate that effectively collects nano-sized PM, which greatly affects the number of particles in the exhaust gas, as compared with Comparative Examples 1 and 2. , It can be seen that the pressure loss at the initial stage of PM collection (1 g / L) is well maintained.

1: Outer wall 2: Partition wall 3: Outflow side sealing flow path 4: Inflow side sealing flow path 6a: Inflow side sealing part 6c: Outflow side sealing part 8: Exhaust gas inflow side end face 9: Outflow side end face 10 : Ceramic honeycomb filter

Claims (3)

A ceramic honeycomb structure having a large number of flow paths formed in the axial direction and partitioned by a porous partition wall, wherein the pore size distribution of the partition wall is large.
Total pore volume: 0.70 to 0.80 cm ³ / g,
Pore volume of 1 μm or more: 0.68 to 0.78 cm ³ / g,
Pore volume of 2 μm or more: 0.65 to 0.75 cm ³ / g,
Pore volume of 5 μm or more: 0.58 to 0.68 cm ³ / g,
Pore volume of 10 μm or more: 0.42 to 0.56 cm ³ / g,
Pore volume of 20 μm or more: 0.06 to 0.19 cm ³ / g,
Pore volume of 30 μm or more: 0.03 to 0.10 cm ³ / g,
Pore volume of 50 μm or more: 0.02 to 0.05 cm ³ / g,
Pore volume of 100 μm or more: 0.010 to 0.035 cm ³ / g,
A ceramic honeycomb structure having a pore volume of 200 μm or more: 0.020 cm ^{3 / g or less.} In the ceramic honeycomb structure according to claim 1,
The difference between the logarithm of the pore diameter d20 where the cumulative pore volume is 20% of the total pore volume and the logarithm of the pore diameter d80 where the cumulative pore volume is 80% σ = log (d20) -log (d80) is 0.40 to 0.60. A ceramic honeycomb structure characterized by. In the ceramic honeycomb structure according to claim 1 or 2.
A ceramic honeycomb structure characterized in that the coefficient of thermal expansion in the flow path direction between 40 and 800 ° C. is 3 × 10 ^-7 / ° C. to 11 × 10 ^{-7 / ° C.}

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