CN100523446C - Ceramic honeycomb filter - Google Patents

Abstract

A ceramic honeycomb filter and its manufacturing method, which is composed of a ceramic honeycomb structure with a porous partition wall that divides a plurality of flow channels, and uses exhaust gas to pass through the porous partition wall to filter out particles contained in the exhaust gas. It is made of heat-resistant ceramics, and it is characterized in that the ends of the predetermined flow passages in the flow passages are sealed, and the flow passages near the outer peripheral wall are sealed at both ends with a sealing material whose length from the filter end surface less than 8.2% of the total length of the device, and the flow passages at both ends of the seal exist within the radial length range from the outer periphery to the center of a maximum of 5x the distance between partition walls.

Description

Ceramic honeycomb filter and manufacturing method thereof

This application is a divisional application of the invention patent application named "ceramic honeycomb filter" and application number 02154555.3 submitted by Hitachi Metals Co., Ltd. and Hino Automobile Co., Ltd. on September 13, 2002.

technical field

The invention relates to a ceramic honeycomb filter for filtering particles contained in exhaust gas of a diesel engine.

Background technique

In order to filter the particulates emitted by diesel engines, a ceramic honeycomb filter with porous partition walls is being studied to filter the exhaust gas containing particulates through the partition walls. Such filters are generally referred to as particulate collection filters (diesel particulate filters). Fig. 2 (a) is a front view of the ceramic honeycomb filter 11 used as a particle collection filter, Fig. 2 (b) is a sectional side view of this part, and Fig. 3 is a schematic sectional view of the ceramic honeycomb filter 11 shown in Fig. 2 . As shown in Figures 2 and 3, the approximately cylindrical ceramic honeycomb filter 11 has an outer wall 11a and a porous partition wall 11b installed inside the outer wall 11a, and the outer wall 11a and the porous partition wall 11b or the adjacent porous partition wall 11b The inflow-side end 11d and the outflow-side end 11e of the surrounding flow path 11c are alternately sealed with sealing materials 12a, 12b. The outer wall 11a of the ceramic honeycomb filter 11 is housed in a metal case 14 in a state of being fixed by fixing members 13a, 13b.

The exhaust gas containing particles enters the flow channel 11c (represented by 10a) from the inflow side open end 11d of the ceramic honeycomb filter 11, passes through the porous partition wall 11b, and then passes through the adjacent flow channel 11c, and is discharged from the outflow side open end 11e ( represented by 10b). In this process, fine particles contained in the exhaust gas are collected in the pores of the porous partition wall 11b. Once the collected particles accumulate excessively in the ceramic honeycomb filter 11 , the pressure drop of the filter 11 will increase and the output power of the engine will decrease. Therefore, external combustion devices such as external electric heaters or burners are generally used to periodically burn the collected particles to regenerate the ceramic honeycomb filter 11 . When using this ceramic honeycomb filter 11 as a particle collection filter, two methods are generally adopted: (a) use a pair of ceramic honeycomb filters, and use the other filter to alternately regenerate when one of the filters is regenerated and (b) the continuous regeneration method of regenerating the filter by burning the particles through the action of the catalyst while collecting the particles.

For such a particle collection filter, the pressure drop, the collection efficiency of the particles, and the possible collection time (the time from the start of particle collection to the pressure drop reaching a certain level) are most important. The collection efficiency and the pressure drop have a reciprocal relationship, the higher the collection efficiency is, the greater the pressure drop will be, and the collection efficiency will decrease when the pressure drop decreases. In order to satisfy the characteristics of such a filter having a reciprocal relationship, studies have been conducted on how to control the porosity and average pore diameter of the porous partition wall of the ceramic honeycomb filter. A study was also conducted on how to satisfy the necessary conditions of being able to burn the fine particles collected by the ceramic honeycomb filter with high efficiency and not be damaged by the thermal stress generated during the combustion process.

Based on this status quo, Japanese Patent No. 3-10365 discloses that the pores of a partition wall are composed of small pores with a diameter of 5-40 μm and large pores with a diameter of 40-100 μm, and the number of small pores is 5-40 times that of the large pores. The exhaust gas purification filter, and it is an exhaust gas purification filter that maintains a high collection rate in the initial stage and has a low pressure drop. The average pore diameter of the pores on the partition wall of this filter is greater than 15 μm, and the cumulative pore volume is preferably in the range of 0.3-0.7 cm ³ /g. Although Japanese Patent No. 3-10365 does not describe the porosity P (volume %) of the partition wall, if the density ρ of the cordierite used in the examples is 2.5 g/cm ³ , it can be calculated according to the cumulative pore volume V (cm ³ /g) The derived formula calculates the porosity P of the partition wall.

The formula is as follows:

P(%)=100Vρ/(1+Vρ)

According to the above formula, the optimum range of cumulative pore volume (0.3-0.7 cm ³ /g) with pores on the partition wall is converted into a porosity of 42.8-63.6% by volume.

Japanese Patent Publication No. 61-54750 discloses that by controlling the porosity and average pore diameter, the filter design from high collection rate to low collection rate can be completed. As the best specific example of No. 61-54750 of Japanese Patent Publication, Fig. 8 shows the porosity and average pore diameter in the areas connecting 1, 5, 6 and 4 points. The porosity and average pore diameter of each point are as follows.

point Porosity (volume%) Average pore size (μm) 1 58.5 1 5 39.5 15 6 62.0 15 4 90.0 1

JP-9-77573 discloses a honeycomb structure, which has a porosity of 55-80% and an average pore diameter of 25-40 μm. Composed of macropores of 100 μm, the number of small pores is 5-40 times that of large pores, and this honeycomb structure has high collection rate, low pressure drop and low thermal expansion rate.

However, although the pressure drop of the filter and the collection efficiency of particles can be balanced to a certain extent by optimizing the porosity, average pore size and partition pore size of the ceramic honeycomb structure, once the porosity and average pore size are increased, The strength of the porous partition walls of the filter inevitably decreases. This is mainly because the strength of the porous partition has a reciprocal relationship with its porosity and average pore diameter. In particular, in order to obtain a filter with low pressure drop, when the porosity exceeds 60% or the average pore diameter exceeds 15 μm, the strength of the porous partition walls decreases significantly. Therefore, it is difficult to obtain a durable ceramic honeycomb filter with low pressure drop and high collection rate, which is not affected by thermal stress and thermal shock when used as a filter for collecting particulates of diesel engines and by assembly. Damaged by mechanical stress caused by fastening and vibration during the time.

When regenerating a conventional honeycomb filter after collecting particles, as shown in FIG. 3, since the exhaust gas passes through the flow channel adjacent to the outer wall 11a, the combustion heat of the collected particles will be dissipated through the outer wall 11a and the fixing members 13a, 13b. Give the metal case. Therefore, since the temperature gradient between the center and the outside of the filter 11 is too large, the filter is broken due to thermal stress, and the external temperature is difficult to rise, so there are problems such as incomplete combustion of particles.

As shown in FIGS. 2 and 3 , in conventional ceramic honeycomb filters, since the outer end surface of the sealing material on the exhaust gas inflow side is flat, particles accumulate on the outer end surface of the sealing material on the inflow side. Furthermore, since the cohesive force of the fine particles is very strong, the accumulation of the fine particles will gradually increase. When the accumulation of fine particles becomes larger, the flow path on the inflow side becomes smaller, and the pressure drop of the filter increases. Ultimately, particulate collection time is shortened and cumbersome filter regeneration is necessary.

Contents of the invention

Therefore, it is an object of the present invention to provide a ceramic honeycomb filter having superior mechanical strength and durability, while prolonging the particle collection time and reducing pressure drop.

In view of the stated purpose, after research, the inventors found the pressure drop, high collection rate and high strength to optimize the regeneration efficiency by reasonably limiting the pore size distribution range of the porous partition wall of the ceramic honeycomb structure and improving the sealing method, thereby obtaining Ceramic honeycomb filter for long-term particle collection.

That is, the ceramic honeycomb filter of the present invention is composed of a ceramic honeycomb structure having a porous partition wall that divides a plurality of flow channels through which exhaust gas passes to filter particles in the exhaust gas, wherein the flow channel is sealed. At the end of the flow channel specified in the channel, in the case of measuring the porous partition wall by mercury intrusion method, its porosity is 60-75% and the average pore diameter is 15-25 μm, relative to the fine pore diameter of the nth test point The maximum value of the gradient Sn of the cumulative pore volume distribution curve of the partition wall is above 0.7, and the gradient of the cumulative pore volume distribution curve is represented by the following formula (1):

Sn=-(V _n -V _n-1 )/[logD _n -log(D _n-1 )] (1)

(where: Dn is the pore diameter (μm) of the nth measurement point,

D _n-1 is the pore diameter (μm) of the n-1th measuring point,

Vn is the cumulative pore volume (cm ³ /g) of the nth measurement point,

Vn-1 is the cumulative pore volume (cm ³ /g) of the n-1th measurement point,

And the material of the ceramic honeycomb filter is composed of cordierite, mullite, alumina, silicon nitride, silicon carbide, aluminum nitride, lithium aluminum silicate, aluminum titanate or zirconia,

The maximum value of the gradient Sn of the cumulative pore volume distribution curve of the porous pore diameter is above 0.9, the porosity of the porous partition wall is 65-70%, and the average pore diameter of the porous partition wall is 18-22 μm, which The main component is substantially a chemical composition consisting of 42-56 mass % of SiO ₂ , 30-45 mass % of Al ₂ O ₃ and 12-16 mass % of MgO, and the main component of the crystal phase is cordierite.

Also, the ceramic honeycomb filter of the present invention is composed of a ceramic honeycomb structure having a porous partition wall that divides a plurality of flow channels, and exhaust gas passes through the porous partition wall to filter out particles in the exhaust gas, wherein the sealed In the end portion of the flow channel defined in the flow channel, the catalyst is held in the porous partition wall, and the porosity of the porous partition wall is 60-75% and the average pore diameter is 15-25 μm when measured by mercury porosimetry The maximum value of the gradient Sn of the cumulative pore volume distribution curve of the partition wall relative to the pore diameter of the nth test point is more than 0.7, and the gradient of the cumulative pore volume distribution curve is represented by the following formula (1):

Sn=-(V _n -V _n-1 )/[logD _n -log(D _n-1 )] (1)

(where: Dn is the pore diameter (μm) of the nth measurement point,

D _n-1 is the pore diameter (μm) of the n-1th measuring point,

Vn is the cumulative pore volume (cm ³ /g) of the nth measurement point,

Vn- ₁ is the cumulative pore volume (cm ³ /g) of the n-1th measuring point,

And the material of the ceramic honeycomb filter is composed of cordierite, mullite, alumina, silicon nitride, silicon carbide, aluminum nitride, lithium aluminum silicate, aluminum titanate or zirconia.

That is, the ceramic honeycomb filter of the present invention is composed of a ceramic honeycomb structure having a porous partition wall that divides a plurality of flow channels, and exhaust gas passes through the porous partition wall to filter particles contained in the exhaust gas. The end of the flow channel is specified in the flow channel, and the flow channel near the outer peripheral wall is sealed with a sealing material at both ends. The flow channel exists within a radial length range from the outer periphery to the center of a maximum of 5×the distance between partition walls.

Here, the length from the end surface of the sealing material that seals the flow channel near the outer peripheral wall at both ends is less than 3.3% of the total length of the ceramic honeycomb filter, and the flow channel near the outer peripheral wall sealed at both ends is from The outer peripheral wall of the end surface of the honeycomb filter faces the center of the end surface of the honeycomb filter, and there is a flow channel within a length range of at most 3x (the distance between partition walls).

Also, it is preferable that the outer peripheral wall of the ceramic honeycomb filter is composed of cordierite particles and colloidal silica present therebetween.

In sealing the end of the flow path with the sealing material, the predetermined opening on one end side of the honeycomb structure is covered with a resin mask, then immersed in the sealing material slurry to a predetermined depth, and removed after the slurry is dried. A resin mask is made, and a sealing material is fired.

The manufacturing method of the ceramic honeycomb filter of the present invention, it extrudes the quantitative mixture of ceramics that can be plasticized into a honeycomb shape and fires it to form a ceramic honeycomb structure, and the flow of the ceramic honeycomb structure The two ends of the channel are alternately sealed, and it is characterized in that, from the outer circumference to the center, the two ends of the flow channel that exist within the range of the radial length of the maximum 5 × partition wall spacing, from the filter end face to the entire length of the filter 8.2% or less of the length is sealed.

It is preferable to seal from the end surface of the filter to a length of 3.3% or less of the total length of the filter, and to extend from the outer periphery to the center at both ends of the flow path that exists within the range of the radial length of a maximum of 3×the distance between partition walls , to seal.

Sealing Material The partition wall of the honeycomb structure having the above structure has a high porosity and a clear pore size distribution, and the proportion of pores close to the average pore size is large. Therefore, the ceramic honeycomb filter of the present invention has low pressure drop and high strength.

Description of drawings

Fig. 1 (a) is a front view showing an embodiment of a honeycomb structure;

Fig. 1(b) is a partial cross-sectional side view of the honeycomb structure in Fig. 1(a);

Figure 2 (a) is a front view showing an embodiment of a filter using a honeycomb structure;

Fig. 2 (b) is a partial cross-sectional side view of the filter in Fig. 2 (a);

Fig. 3 shows the schematic cross-sectional view of the waste gas flowing into the ceramic honeycomb filter;

Fig. 4 is a graph showing the relationship between the pore diameter and the gradient Sn of the cumulative pore volume distribution curve obtained by the mercury intrusion penetration method;

Fig. 5 is a graph showing the relationship between the gradient Sn maximum value of the cumulative pore volume distribution curve and the A-axis compressive strength;

6 is a graph showing the relationship between the pore diameter of the honeycomb structure in Examples 1 and 2 and Reference Example 1 and the gradient Sn of the cumulative pore volume distribution curve;

Fig. 7 is a side view showing another example in the ceramic honeycomb filter of the present invention;

Fig. 8 is the A-A sectional view of Fig. 7;

Figure 9 (a) is a partial cross-sectional side view showing another embodiment of the ceramic honeycomb filter of the present invention;

Fig. 9 (b) is a partial cross-sectional side view showing another embodiment of the ceramic honeycomb filter of the present invention;

Fig. 9 (c) is a partial cross-sectional side view showing another embodiment of the ceramic honeycomb filter of the present invention;

Fig. 9 (d) is the partial end face side view showing another embodiment in the ceramic honeycomb filter of the present invention;

Fig. 10 is a graph showing the relationship between the cumulative pore volume of the honeycomb structures obtained in Examples 1 and 2 and Reference Example 1 and the set value of the mercury porosimetry;

Fig. 11 is a particle size distribution diagram of a pore former.

Detailed ways

In the present invention, the following formula (1) is used for the cumulative pore volume curve of the partition wall of the honeycomb structure (the curve represented by a graph with the horizontal axis as the pore diameter and the vertical axis as the cumulative pore volume):

Sn=-(Vn-V _n-1 )/[logDn-log(D _n-1 )] (1)

(where: Dn is the pore diameter (μm) of the nth measurement point,

D _n-1 is the pore diameter (μm) of the (n-1)th measuring point,

Vn is the cumulative pore volume (cm ³ /g) of the nth measurement point,

V _n-1 is the cumulative pore volume (cm ³ /g) of the (n-1)th measurement point,

Sn is the gradient of the cumulative pore volume distribution curve of the nth measurement point relative to the pore diameter. ) indicates that the maximum value of Sn is greater than 0.7. The reason for this is as follows,

The strength of the ceramic honeycomb structure depends not only on the porosity and average pore size, but also on the pore size distribution. In particular, a high-strength ceramic honeycomb structure can be obtained with a porosity of 60% or more and an average pore diameter of 15 μm or more due to a sharp change in pore size distribution (by increasing the uniformity of pore size).

The porosity, average pore diameter, and gradient Sn of the cumulative pore volume distribution curve of the ceramic honeycomb structure were measured by mercury porosimetry using an automatic corkscrew (O-topoa) III9410 manufactured by Micromeritics. When the mercury intrusion method is used, the sample is first put into the measuring tank, after the tank is decompressed, mercury is introduced and pressurized, and the pore diameter and cumulative pore volume are obtained from the pressure and the volume of mercury pressed into the pores of the sample. Relationship. When the pressure is increased, the mercury will penetrate into the finer pores, and the volume of the finer pores corresponding to the pressure is measured. Therefore, measurement data can be obtained in order from large pore diameters to small pore diameters.

From the pore diameter Dn-1 and the cumulative pore volume Vn-1 of the (n-1) measuring point at the beginning of the measurement and the pore diameter Dn and the cumulative pore volume Vn of the (n) measuring point, the above formula ( 1) Obtain the gradient Sn of the nth measuring point. An example of the measurement results of Sn is shown in FIG. 4 . In _{Fig .} 4, _point a is the gradient S1 [(V _{1 -V 2} )/( logD _{1 -logD 2} ) _] , point b _is the gradient S2 [( _{V 2 -V 3} )/(logD ₂ -logD ₃ )]. The distribution of the gradient Sn of the cumulative pore volume distribution curve shown in Figure 4 shows that if the maximum value of Sn is less than 0.7, the pore size distribution range is wide, and if the maximum value of Sn is greater than 0.7, the pore size distribution range is very narrow.

If the pore size distribution range is wide, the strength will decrease due to the increase of large and large pores, and the proportion of fine pores that cause the increase in pressure drop due to the clogging of pores by fine particles increases. Therefore, it is difficult to make low pressure drop and high strength coexist at the same time. In contrast, if the maximum value of Sn is greater than 0.7, since the pore size distribution is very narrow, the ratio of coarse pores to fine pores can be reduced, so that low pressure drop and high strength can coexist. This can be seen from FIG. 5 which shows the relationship between the maximum value of the gradient Sn of the cumulative pore volume distribution curve and the relative value of the A-axis compressive strength. It can be seen from Figure 5 that when the maximum value of Sn is greater than 0.7, the A-axis compressive strength value is more than 1.5 times the strength value of existing products (such as when the maximum value of Sn is below 0.6). That is, it can be seen that when the maximum value of Sn exceeds 0.7, the mechanical strength of the ceramic honeycomb structure is significantly improved. In order to obtain both low pressure drop and high strength, the maximum value of Sn is preferably greater than 0.9.

The porosity of the ceramic honeycomb structure is within 60-75%. When the porosity is lower than 60%, the pressure drop of the filter will be too high, and when it exceeds 75%, not only the strength of the filter will be reduced, but also the collection efficiency of particles will be reduced accordingly. The pressure drop of the filter is lower when the porosity is above 65%. In addition, when the porosity is below 70%, the strength of the filter and the particulate collection efficiency are further reduced. Therefore, the optimum range of porosity should be 60-75%.

The average pore size of the pores in the ceramic honeycomb structure is 15-25 μm. When the average pore size is less than 15 μm, the pressure drop of the filter will be too high, and if it exceeds 25 μm, not only the strength of the filter will be reduced, but also the particle collection efficiency will be reduced because the extremely small particles cannot be collected. In order to obtain the reciprocal characteristics of low pressure drop and high strength at the same time, the optimum range of average pore size should be 18-22μm.

The main chemical components of the porous ceramics constituting the ceramic honeycomb structure are essentially composed of 42-56% by mass of SiO ₂ , 30-45% by mass of Al ₂ O ₃ and 12-16% by mass of MgO. The main component is preferably cordierite. The ceramic honeycomb filter of the present invention utilizes the low thermal expansion characteristic of cordierite itself, and is hard to break even when thermal shock is applied. But the present invention is not limited to the use of cordierite, and other heat-resistant ceramics can also be used, such as mullite, alumina, silicon nitride, silicon carbide, aluminum nitride, lithium aluminum silicate, aluminum titanate, materials such as zirconia.

When the filter is regenerated, in order to burn particles with high efficiency, (a) seal the two ends of the flow channel near the outer wall of the filter with a sealing material, (b) the length from the end face of the filter of the sealing material is less than 8.2% of the total length of the filter, And (c) it is advisable to set the length of the flow passage sealed at both ends within the radial length range from the outer wall to the center, which is at most 5x the distance between partition walls. The reason is that since the exhaust gas does not flow into the flow passages sealed at both ends, the sealed flow passages can function as a heat-insulating air layer, and heat radiation from the outer wall of the filter to the metal casing can be suppressed, so that the collected waste can be burned efficiently. of particles. In addition, by providing flow passages sealed at both ends, the pressure drop of the filter can be suppressed to the maximum extent, preventing engine performance from deteriorating.

By keeping the length from the filter end face of the sealing material at both ends of the sealing flow path within 8.2% of the total filter length, it is possible to negligibly suppress the emission of combustion heat of particles to the metal case through the sealing material. When the length of the sealing material from the end face of the filter exceeds 8.2% of the total length of the filter, the heat of combustion of the particles cannot be ignored to the metal shell, and the incomplete combustion of the collected particles will lead to a decrease in the regeneration rate of the filter.

Since the length of the flow channel sealed at both ends is set within the radial length range of the maximum 5x partition spacing from the outer wall to the center, the pressure drop of the filter can be suppressed to a minimum. However, if the length of the flow channel sealed at both ends exceeds the radial length range of the maximum 5x partition spacing from the outer wall to the center, the proportion of partitions with filter function will be relatively reduced, resulting in an increase in the pressure drop of the filter.

The length from the filter end surface of the sealing material at the two ends of the flow passage near the outer wall of the filter is preferably less than 3.3% of the total length of the filter. As a result, the flow channel near the outer wall of the filter will have a greater effect of insulating the air layer, and the heat emitted from the outer wall of the filter to the metal casing will be further reduced, and the collected particles can be burned more efficiently, improving the regeneration rate of the filter. will be further improved.

The length of the flow channel near the outer wall sealed at both ends is controlled within the radial length range of the maximum 3x partition spacing from the outer wall to the center, thereby further reducing the pressure drop of the filter. As a result, engine back pressure is reduced, further improving engine performance.

The ceramic honeycomb structure of the present invention can be produced by the following process. First, add a pore-forming material with a porosity in the range of 60-75% after sintering to the ceramic raw material powder, the average particle size of the pore-forming material is above 20 μm, especially in the range of 40-80 μm and the particle size is 20 μm. -100 μm accounts for more than 50%. If necessary, molding aids such as binders and lubricants are mixed in the mixture, and water is added to prepare a plasticized quantitative mixture. The quantitative mixture is extruded to form a formed body with a honeycomb structure, and after drying, the pore-forming material is burned to remove it. Next, the molded body is sintered to obtain a ceramic honeycomb structure having micropores inherent to ceramics and pores formed by removing the pore-forming material in the partition walls. In this way, the ceramic product passes through the combination of the original micropores and the pores formed by the pore-forming material (the average particle size is more than 20 μm, and the particle size is 20-100 μm accounts for more than 50%). The average particle size of the partition wall The pore size can be controlled within the range of 15-25 μm, and at the same time, the maximum value of Sn, which represents the inclination of the pore size distribution, can be controlled above 0.7. Especially for cordierite ceramics, since it itself has a pore size of 1-20 μm, it has the best effect when combined with a pore-forming material with an average particle size of 20 μm or more and a particle size of 20-100 μm accounting for more than 50%.

The pore-forming material is graphite, wheat flour, resin powder, etc., preferably classified to form a particle size distribution with an average particle size of 20 μm or more, and a particle size of 20-100 μm accounting for more than 50%. In addition, when using resin powder, by adjusting its production conditions, it is also best to achieve a particle size distribution with an average particle size of 20 μm or more and a particle size of 20-100 μm accounting for more than 50%.

If the pore-forming material is approximately spherical, the pores formed in the cell walls will also be approximately circular, so stress concentration on the pores can be reduced, and a honeycomb structure with excellent mechanical strength can be produced. In addition, if the pore-forming material is a hollow body, it is easy to burn and remove the pore-forming material. Therefore, when the pore-forming material is burned and removed, there will be no cracking problem in the partition wall, and the production yield can be improved.

The present invention will be described in detail through the following specific examples herein, but the present invention should not be limited thereto.

Embodiment 1 and 2, reference example 1

In order to manufacture cordierite with the main components of SiO ₂ by mass 49-51%, Al ₂ O ₃ by mass 35-37%, and MgO by mass 13-15%, kaolin powder, calcined kaolin powder, alumina powder , aluminum hydroxide powder, silica powder and talc powder are quantitatively mixed and added into binder, lubricant and spherical resin powder used as a pore-forming agent. Water is added to the resulting mixture to make a plasticizable dosing mixture. The quantitative mixture is pressed into a cylindrical honeycomb and dried.

The particle size distribution of spherical resin powder used as a pore former is shown in FIG. 16 . In addition, the average particle size of the spherical resin powder and the particle size ratio of 20-100 μm are shown in the table below.

Porogen Average particle size (μm) Particle size ratio of 20-100μm (mass%) Example 1 64 75 Example 2 62 62 Example 3 52 48

The resulting molded body was sintered at a temperature of 1350-1440° C., as shown in FIG. 1 , to produce various cordierite material honeycomb structures 10 composed of porous ceramic partition walls 3 and through holes 2 . The obtained honeycomb structure 10 had a diameter of 143 mm, a length of 152 mm, a partition wall thickness of 0.3 mm, and the number of flow channels per 1 cm ² was 46.

The honeycomb structures of Examples 1 and 2 and Reference Example 1 were manufactured by adjusting the particle size and proportion of ceramic raw material powder, particle size and addition amount of pore-forming material, forming conditions, and sintering conditions. The micropore diameters of various ceramic honeycomb structures were measured by mercury porosimetry using an automatic corkscrew III9410 manufactured by Micromeritics. The relationship between the obtained cumulative pore volume and the mercury pressure setting value is shown in Fig. 10 . The relationship between the pore diameter and the set pressure is as follows: pore diameter=-4αcosθ/P (where: α is the surface tension of mercury; θ is the contact angle between mercury and solid, and P is the set pressure.). Since 4αcosθ is a constant, the pore size is inversely proportional to the set pressure. In addition, the cumulative pore volume is the volume of pressed mercury/weight of the sample. It can be seen from Figure 10 that between about 10 μm and about 100 μm, the gradient of the cumulative pore volume distribution curve in the sample of Example 1 is very inclined, and the gradient of the cumulative pore volume distribution curve of the sample of Example 2 is also very inclined, but refer to The gradient of the cumulative pore volume distribution curve of the sample in Example 1 is gentler.

In the same manner as above, the maximum value of the gradient Sn of the porosity, average pore diameter, and cumulative pore volume distribution curve of each sample was obtained. In addition, the smooth curve can be obtained from the graph of the measurement data, and the gradient Sn of the cumulative pore volume distribution curve can be obtained from the difference in the cumulative pore volume at the same minute interval as the pore diameter on the curve. However, as can be seen from Figure 10, since the curve is very smooth, and the logarithms of the pore diameters involved in the measurement points actually have equal intervals, even if the pore diameters of the nth measurement point and the (n-1)th measurement point are used The data obtains the gradient Sn, and there is almost no error. The results obtained are shown in Table 1. In addition, the relationship between the pore diameter of the partition wall and the gradient Sn of the cumulative pore volume distribution curve in each honeycomb structure is shown in FIG. 6 .

As shown in FIGS. 2( a ) and ( b ), the porous cordierite honeycomb filter 11 can be obtained by sealing the flow channel openings at both ends of each honeycomb structure with sealing materials 12 a and 12 b. Table 1 shows the pressure drop and damage resistance evaluation results of various filters 11 .

On the pressure drop test bench, the pressure drop is measured by making the gas quantitatively flow into the honeycomb filter, and the following standards are used for evaluation.

◯: The pressure drop is not more than the practical allowable value (pass).

X: The pressure drop exceeds the practical allowable value (unacceptable).

Regarding the breakage resistance, the A-axis compressive strength of each filter was measured according to the standard M505-87 "Test method for ceramic monolithic (ceramic monolith) substrates for automobile exhaust gas purification catalysts" prepared by the Association of Automotive Technology, and the A-axis was evaluated according to the following criteria The relative value of compressive strength (taking the existing product level index as 1.0).

⊚: A-axis compressive strength is 2.0 or more (pass).

◯: The A-axis compressive strength is less than 2.0 and more than 1.5 (pass).

×: A-axis compressive strength is less than 1.5 (unacceptable).

Based on the pressure drop and breakage resistance, comprehensive evaluation was performed according to the following criteria.

◎: When the pressure drop is o and the breakage resistance is ◎.

○: When both the pressure drop and the breakage resistance are ○.

×: When one of the pressure drop and the breakage resistance is unacceptable.

Table 1

Note: (1) The gradient of the cumulative pore volume distribution curve

It can be seen from Table 1 that in Examples 1 and 2, because the maximum value of Sn is above 0.7, even if the porosity exceeds 60% and the average pore diameter is 15-25 μm, the pressure drop of the filter is small and the damage resistance is also good. It is qualified, and the comprehensive evaluation is ◎ and ○ respectively.

In addition, since the ceramic honeycomb filter of Reference Example 1 had a maximum value of Sn of less than 0.7, the pressure drop was acceptable, but the fracture resistance was unacceptable (×), and the overall evaluation was ×.

Example 3-7

Make the same plasticized quantitative mixture as in Example 1, and use the extrusion molding method to make a cylindrical honeycomb structure from the quantitative mixture. In order to obtain various wall thicknesses and the number of runners per 1 cm ² , the size of the forming die was adjusted. Each molded body was sintered at a temperature of 1350-1440° C. to produce the cordierite honeycomb structures of Examples 3-7 having various porous partition walls and through holes. The diameter of each honeycomb structure is 143 mm, the length is 152 mm, the thickness of the partition wall is 0.15-0.33 mm, and the number of flow channels per 1 cm ² is 39-62. In addition, the porosity of each honeycomb structure was 65%, the average pore diameter was 20.8%, and the maximum value of the gradient Sn of the cumulative pore volume distribution curve was 1.12.

Both ends of the filter were sealed in the same manner as in Example 1 to produce a cordierite honeycomb filter. In the same manner as in Example 1, the pressure drop and breakage resistance of each filter were measured. The results are shown in Table 2. As can be seen from Table 2, the overall evaluations of the cordierite honeycomb filters of Examples 3-7 are both ◎ and ○.

Table 2

Embodiment 8 and embodiment 9, reference example 2

As a ceramic material with a high proportion surface area, activated alumina powder and alumina glue with a central particle diameter of 5 μm are mixed into water to obtain activated aluminum powder slurry. As in Examples 1 and 2 and Reference Example 1, this slip was coated on a ceramic honeycomb structure. After removing excess slurry, apply it repeatedly, and finally apply 60g/L activated aluminum to the honeycomb structure. The honeycomb structure was dried at 120°C and then sintered at 800°C. Further, the honeycomb structure was immersed in a platinum chloride hydroxide solution, dried at 120°C, and then fired at 800°C. A ceramic honeycomb filter with about 2 g/L of platinum catalyst was thus produced.

The same method as in Example 1 was used to measure the pressure drop of the ceramic honeycomb filter with platinum catalyst. The pressure drop of the ceramic honeycomb filter with platinum catalyst was evaluated according to the same standard as in Example 1. In addition, on the pressure drop test bench, the quantitative gas containing carbon powder flows through the honeycomb filter, so that the filter collects carbon powder. Measure the pressure drop before and after carbon powder collection, obtain the pressure drop difference ΔP (pressure drop after carbon powder collection, pressure drop before carbon powder collection), and use the following standards for evaluation. The results are shown in Table 3.

o: The pressure drop is below the practical allowable value (pass).

X: The pressure drop exceeds the practical allowable value (unacceptable).

table 3

Example NO Pressure drop with catalyst Pressure drop ΔP Example 8 ○ ○ Example 9 ○ ○ Reference example 2 x x

The pressure drop of the ceramic honeycomb filter in Example 8 and Example 9 did not increase due to the presence of the catalyst, and the evaluation of the pressure drop with the catalyst was all qualified (○). On the other hand, the pressure drop of the ceramic honeycomb filter of Reference Example 2 was greatly increased due to the presence of the catalyst, so the pressure drop evaluations were all unacceptable (×).

For the ceramic honeycomb filters of Examples 8 and 9, the pressure drop difference ΔP before and after the carbon powder collection is qualified (○) within the allowable practical range. In reference example 2, the pressure drop difference ΔP before and after carbon powder collection exceeds the practical allowable range, which is unqualified (×).

As can be seen from the above, the ceramic honeycomb filter (embodiment 8 and embodiment 9) with the gradient Sn maximum value of the cumulative pore volume distribution curve above 0.7, even after having a catalyst, the increase in pressure drop is also small, and Excellent filter performance due to less pressure drop rise through toner collection.

Implementation 10-14, Reference Example 3-7

Mix cordierite raw material powders with the same composition as in Example 1, and extrude to make a honeycomb shaped body, and then sinter at 1400°C to make an outer diameter of 267mm, a length of 305mm, and a partition wall thickness of 0.3mm. , a honeycomb structure made of cordierite with a partition wall pitch of 1.47 mm and a peripheral wall thickness of 1.5 mm.

In order to seal the ends of the flow channels of the cordierite honeycomb structure alternately and at the same time to seal both ends of the flow channels near the outer wall, a sealing slurry made of cordierite raw material should be filled behind the flow channel ends of the cordierite honeycomb structure , dried and sintered to make a cordierite honeycomb filter with a total length of 305 mm. In order to adjust the length from the end face of the filter that seals the sealing material at both ends of the flow channel near the outer peripheral wall and the range in which the flow channels at both ends of the seal exist (expressed in the radial direction length from the outer peripheral wall to the center at the end face), and adjusted Filling condition of seal slurry.

Diesel engine exhaust gas containing particulates is passed through the resulting cordierite honeycomb filter to collect the particulates and burn the particulates to regenerate the filter. The measurement results of regeneration rate and pressure drop are shown in Table 4. In Table 4, the relative length of the sealed flow channel at both ends is [(the length from the filter end surface of the sealing material at both ends of the flow channel near the sealed peripheral wall)/(full length of the filter)] x 100. In addition, the so-called range of the sealed flow passages at both ends on the end surface represents the existence range of the sealed flow passages at both ends by the length in the radial direction from the outer wall to the center.

The regeneration rate is [(amount of collected particles-amount of remaining particles after regeneration)/(amount of collected particles)]x100(%). The regeneration rate was evaluated using the following criteria.

⊚: When the regeneration rate is 90% or more (pass).

◯: When the regeneration rate was 80% or more (pass).

×: When the regeneration rate is less than 80% (failure).

Measure the pressure drop with a gas flow rate of 7.5Nm ³ /min, and evaluate it according to the following standards.

◎: When the pressure drop is below 200 mmAq (pass).

○: When the pressure drop is 200mmAq-250mmAq (pass).

×: When the pressure drop exceeds 250 mmAq (failure).

The comprehensive evaluation was performed according to the following criteria.

◎: When both regeneration rate and pressure drop are ◎.

○: When both regeneration rate and pressure drop are acceptable.

×: When even one of regeneration rate and pressure drop is unacceptable.

As can be seen from Table 4, in Examples 10-14, the length from the filter end surface of the sealing material at the two ends of the sealing material near the outer peripheral wall is less than 8.2% of the total length of the filter. From the outer peripheral wall to the center, within the range of the maximum 5x partition spacing, the regeneration rate and pressure drop are ○ or ◎ qualified, and the comprehensive evaluation is also qualified. Especially in Example 13, because the length from the filter end surface of the sealing material at both ends of the flow channel near the sealing outer peripheral wall is less than 3.3% of the total length of the filter, and the flow channel near the outer wall at both ends of the seal is from the outer wall to the center. The necessary conditions for the range of maximum 3x partition spacing are all satisfied, so the regeneration rate, pressure drop and comprehensive evaluation are all ◎.

In reference examples 3-7, the length from the filter end surface of the sealing material at both ends of the flow channel near the outer peripheral wall exceeds 8.2% of the total length of the filter, so when the particles burn, the combustion heat of the sealing material is more dissipated, and regeneration The rate is unqualified (×), and the comprehensive evaluation is also ×.

In particular, in Reference Example 6, the flow passage near the outer peripheral wall at both ends of the seal is out of the range from the outer wall to the center of a maximum of 5 x the distance between the partition walls. Therefore, although the heat insulation effect of the flow channels near the two ends of the sealed outer wall is greater, and the regeneration rate is ◎, the number of flow channels that play a filtering function is substantially reduced, so the pressure drop is unqualified (×), and the comprehensive evaluation is also unqualified ( ×).

In the filter of Reference Example 7, the regeneration rate was unacceptable (×) and the overall evaluation was unacceptable (×) because there was no flow passage sealed at both ends near the outer wall, and the heat insulation effect was not achieved through the outer peripheral wall.

Example 15, 16

In the same manner as in Example 10, cordierite raw material powder was mixed, and a honeycomb structure was formed by extrusion molding. After the two ends of the honeycomb structure are sealed to define flow channels, they are sintered at a temperature of 1400° C. to form a cordierite honeycomb sintered body. A slurry obtained by adding a binder and water to 100 parts by mass of cordierite aggregates (average particle diameter 15 μm) and 10 parts by mass of colloidal silica was applied to the outer peripheral surface of the sintered body from which the edge was removed by machining , forming the peripheral wall. Thereafter, the outer peripheral wall was dried and sintered to obtain a cordierite honeycomb filter having the following dimensions.

Outer diameter: 267mm;

Overall length: 305mm;

Partition wall thickness: 0.3mm;

Interval spacing: 1.47mm; and

Peripheral wall thickness: 1.5mm.

According to the same method as in Example 4, the regeneration rate and pressure drop of each honeycomb filter were evaluated. The results are shown in Table 4. In any one of Examples 15 and 16, the length from the filter end surface of the sealing material at both ends of the flow channel near the outer peripheral wall is less than 8.2% of the total length of the filter, and the length near the outer peripheral wall at both ends of the seal is The range conditions of the maximum 5x partition spacing from the outer wall to the center of the flow channel are met. As a result, the regeneration rate and the pressure drop of the filters of Examples 15 and 16 were both ◯ or ⊚ acceptable, and the overall evaluation was also acceptable.

Table 4

Note: Pp is the distance between partition walls.

Sealing material

Fig. 7 shows another example of the ceramic honeycomb filter of the present invention. FIG. 8 is a cross-sectional view along line A-A of FIG. 7 . The dotted line 30 indicates the length in the radial direction from the outer wall 11a to the center direction of 2×the distance between the partition walls, and both ends of the flow path existing in the range between the dotted line 30 and the outer peripheral wall 11a are sealed. As an example of the filter 11 having flow passages at both ends sealed in the vicinity of the outer wall 11a, in addition to the examples shown in FIGS. 7 and 8, FIGS. 9(a)-(d) illustrate other examples.

Although the present invention has been described with reference to the drawings, the cross-sectional shape of the ceramic honeycomb structure is not limited to a circle, and other shapes such as an ellipse may be employed.

In the ceramic honeycomb structure of the present invention, since the maximum value of the gradient Sn of the cumulative pore volume distribution curve of the partition wall pores is 0.7 or more, even if a large porosity of 60-75% is used, and a large average of 15-25 μm The aperture ratio, when used as a diesel particulate filter, can also satisfy the so-called reciprocal characteristics of low pressure drop and high collection efficiency. Moreover, thermal stress and thermal shock stress during use, mechanical fastening force during assembly, and mechanical stress due to vibration will not damage the ceramic honeycomb filter of the present invention, and it has good durability. In addition, the ceramic honeycomb filter of the present invention may collect particles for a long time, and the particles can be removed with high efficiency when the filter is regenerated.

Claims (7)

1. A ceramic honeycomb filter, which is composed of a ceramic honeycomb structure having a porous partition wall that divides a plurality of flow channels, and uses exhaust gas to pass through the porous partition wall to filter out particles contained in the exhaust gas, characterized in that, The main components of the crystalline layer of the ceramic honeycomb filter are cordierite, mullite, alumina, silicon nitride, silicon carbide, aluminum nitride, lithium aluminum silicate, aluminum titanate or zirconia, sealing the The end of the flow channel is specified in the flow channel, and the flow channel near the outer peripheral wall is sealed with a sealing material at both ends. The flow channel exists within a radial length range from the outer periphery to the center of a maximum of 5×the distance between partition walls. 2. The ceramic honeycomb filter according to claim 1, characterized in that the length from the end face of the sealing material sealing the flow channel near the outer peripheral wall at both ends is 3.3% of the total length of the ceramic honeycomb filter. %the following. 3. The ceramic honeycomb filter according to claim 1, characterized in that the flow channel near the outer peripheral wall sealed at both ends is from the outer peripheral wall of the end face of the honeycomb filter toward the center of the end face of the honeycomb filter , Runners that exist in the length range of the maximum 3x partition wall spacing. 4. The ceramic honeycomb filter according to any one of claims 1 to 3, wherein the outer peripheral wall of the ceramic honeycomb filter is composed of cordierite particles and colloidal silica present therebetween. 5. A method for manufacturing a ceramic honeycomb filter, which extrudes a plasticizable ceramic quantitative mixture into a honeycomb shape and fires it to form a ceramic honeycomb structure, and the ceramic honeycomb structure The two ends of the flow channel are alternately sealed, and it is characterized in that the main components of the crystalline layer of the ceramic honeycomb filter are cordierite, mullite, alumina, silicon nitride, silicon carbide, aluminum nitride, lithium Aluminum silicate, aluminum titanate or zirconia, and from the outer circumference to the center, the two ends of the flow channel that exist within the range of the radial length of the maximum 5× partition spacing, from the filter end face to 8.2 of the total length of the filter % below the length of the seal. 6. The method of manufacturing a ceramic honeycomb filter according to claim 5, wherein the sealing is carried out from the end surface of the filter to a length of 3.3% or less of the total length of the filter. 7. The manufacturing method of the ceramic honeycomb filter according to claim 5, characterized in that, from the outer circumference to the center, the two ends of the flow channel existing in the range of the radial length of the maximum 3× partition spacing are carried out. seal.

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