JP2020054985A - Exhaust gas cleaning filter and manufacturing method of exhaust gas cleaning filter - Google Patents

Abstract

To provide an exhaust gas cleaning filter which can collect PM at a high collection rate even when porosity is increased.SOLUTION: An exhaust gas cleaning filter 1 includes a skin 11, a barrier wall 12, and a cell 13. The barrier wall 12 is porous and partitions an inner side of the skin 11 into a plurality of cells 13. The barrier wall 12 has a plurality of communication pores 122 which communicate between the cells 13 adjacent to the barrier wall. Tortuosity L/T defined by a ratio of an average flow passage length L μm of the communication pore 122 to a thickness T μm of the barrier wall 12 satisfies a relation of L/T≥1.1. The exhaust gas cleaning filter is manufactured by using porous silica of which a tap bulk density is a predetermined value or less.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an exhaust gas purification filter having an outer skin, a porous partition partitioning the inside thereof, and cells surrounded by the partition, and a method for manufacturing the exhaust gas purification filter.

  Exhaust gas emitted from an internal combustion engine such as a diesel engine or a gasoline engine, or a heat engine such as a boiler contains particulate matter called particulates. Particulates are hereinafter referred to as “PM” as appropriate. An exhaust gas purifying filter is used to trap PM in exhaust gas.

  An exhaust gas purification filter generally has a plurality of cells formed by being partitioned by a porous partition, and a sealing portion that seals one of both ends of the cell. In the exhaust gas purifying filter, it is required to reduce the pressure loss while increasing the PM collection rate. The PM collection rate is hereinafter appropriately referred to as “collection rate”, and the pressure loss is hereinafter appropriately referred to as “pressure loss”. To reduce the pressure loss, it is effective to increase the porosity of the partition walls. However, when the porosity is increased, the trapping rate tends to decrease.

  In recent years, attempts have been made to improve the trapping rate while increasing the porosity by defining the internal structure of the porous partition wall. For example, Patent Literature 1 discloses a technique for increasing the network length of a network obtained by thinning a 3D model of a ceramic portion in a honeycomb wall. According to the document, by adopting the above configuration, the shape of the honeycomb wall becomes complicated, and particles such as soot can be collected with high efficiency even if the porosity is increased.

JP 2017-164691 A

  However, PM is mainly collected when passing through pores communicating with the partition walls. Therefore, the structure of the pores effective for trapping PM is a continuous vent structure, which is a pore connected from the gas inlet side to the gas outlet side of the partition wall, but the network structure of the ceramic part is the same as the continuous vent structure. Do not always match. Therefore, in the technique of increasing the length of the network of the ceramic portion as in the cited document 1, the structure of the continuous ventilation hole for trapping PM is not sufficiently adjusted. In other words, even if the network of the ceramic part is lengthened, the structure of the continuous ventilation hole which becomes the passage of PM is not necessarily complicated, and there is a limit to the improvement of the trapping rate.

  The present invention has been made in view of such a problem, and an object of the present invention is to provide an exhaust gas purification filter that can capture PM at a high collection rate even if the porosity is increased.

One embodiment of the present invention provides an outer skin (11),
A porous partition (12) that partitions the inside of the outer skin into a plurality of cells (13);
The partition has a plurality of communicating holes (122) for communicating between the cells adjacent to the partition,
The exhaust gas purifying filter (1), wherein the degree of flexure L / T defined by the ratio of the average flow path length Lμm of the communicating holes to the thickness Tμm of the partition wall satisfies the relationship of the following equation (1).
L / T ≧ 1.1 Expression 1

Another aspect of the present invention is a method for producing an exhaust gas purification filter (1),
A mixing step of preparing a cordierite forming raw material by mixing porous silica having a tap bulk density of 0.38 g / cm ³ or less, talc, and an Al source;
Forming a kneaded clay containing the cordierite forming raw material, a forming step of forming a molded body by forming the kneaded clay,
And a baking step of baking the molded body.

  The exhaust gas purification filter has the outer cover, the partition wall, the cell, and the communication hole having the above-described configuration, and the degree of bending L / T defined by the ratio of the average flow path length Lμm of the communication hole to the thickness Tμm of the partition wall is expressed by Expression 1. Satisfy the relationship. That is, the average flow path length L μm of the continuous ventilation hole is 1.1 times or more the thickness T μm of the partition wall. In the partition having such a configuration, the continuous ventilation hole is bent.

  The trapping rate of the exhaust gas purification filter depends on the frequency of collision of the PM with the partition wall. However, by setting the degree of bending to 1.1 or more, the structure of the communicating vent hole which becomes the passage of the PM becomes complicated, and the inside of the communicating vent hole becomes complicated. This leads to an increase in the frequency of PM collisions. It is considered that this is because the frequency of the inertial collision of the PM increases due to the bending of the continuous ventilation hole. As a result, the exhaust gas purification filter exhibits a high trapping rate, and can exhibit a high trapping rate even when the porosity is increased.

  The manufacturing method includes a mixing step, a forming step, and a firing step. In the mixing step, porous silica, talc, and an Al source are mixed. Thereby, a cordierite forming raw material is produced. In the forming step, a kneaded material containing a cordierite forming raw material is prepared, and the kneaded material is formed. Thereby, a molded body is produced. In the firing step, the molded body is fired. Thereby, an exhaust gas purification filter can be obtained.

In the mixing step, porous silica having a tap bulk density of 0.38 g / cm ³ or less is used. Thereby, the volume ratio occupied by the porous silica in the cordierite forming raw material can be increased. As a result, the degree of bending L / T of the continuous vent can be increased. Thereby, for example, an exhaust gas purification filter satisfying the relationship of L / T ≧ 1.1 can be manufactured. As a result, it is possible to obtain an exhaust gas purifying filter having a high trapping rate.

As described above, according to the above aspect, it is possible to provide an exhaust gas purification filter capable of collecting PM at a high collection rate even if the porosity is increased.
Note that reference numerals in parentheses described in the claims and means for solving the problems indicate the correspondence with specific means described in the embodiments described below, and limit the technical scope of the present invention. Not something.

FIG. 2 is a perspective view of an exhaust gas purification filter according to the first embodiment. FIG. 2 is an enlarged partial cross-sectional view in the axial direction of the exhaust gas purification filter according to the first embodiment. (A) It is an example of an enlarged sectional schematic diagram of the partition of an exhaust gas purification filter in Embodiment 1, (b) It is another example of the enlarged sectional schematic diagram of the partition of an exhaust gas purification filter in Embodiment 1. 3A is a schematic cross-sectional view of a partition wall showing the pores of FIG. 3A more simply, and FIG. 3B is a schematic cross-sectional view of a partition wall showing the pores of FIG. 3B more simply. FIG. 4 is an explanatory diagram regarding a CT scan of a partition wall in the first embodiment. FIG. 3 is a diagram illustrating an example of a scan image of a partition wall by a CT scan according to the first embodiment. FIG. 7 is an enlarged view of the scan image shown in FIG. 6. FIG. 3 is a diagram illustrating an example of a binarized image of a CT scan image of a partition wall and a CT scan image of a partition wall in a first embodiment. FIG. 4 is a diagram showing a sampling position of a measurement sample for measuring a degree of bending in the first embodiment. It is an expanded section of a partition in Embodiment 2, and is a figure showing typically the position of the neck inside the communicating vent. FIG. 9 is a CT scan image of a partition wall in Embodiment 2, showing a position of a neck portion in a continuous ventilation hole. FIG. 5 is a cross-sectional view of a neck diameter measuring jig on which a test piece is installed in Experimental Example 1. FIG. 9 is a diagram showing a pressure curve represented by a relationship between a pressure and a flow rate in Experimental Example 1. FIG. 7 is a diagram illustrating a relationship between neck diameter and frequency in Experimental Example 1. FIG. 4 is a diagram illustrating the relationship between the degree of bending and the collection rate in Experimental Example 1. FIG. 6 is a diagram illustrating a relationship between a degree of bending and a pressure loss in Experimental Example 1. FIG. 4 is a diagram showing the relationship between the average neck diameter Φ ₁ / the average pore diameter Φ ₂ and the collection rate in Experimental Example 1. FIG. 4 is a relationship diagram between average neck diameter Φ ₁ / average pore diameter Φ ₂ and pressure loss in Experimental Example 1. In Experimental Example 2 illustrates the relationship between the tap bulk density TD _S and the collection rate of the porous silica. In Experimental Example 2, the ratio PD _M / TD _ST of the tap bulk density TD _ST g / cm ³ of pressurized圧嵩density PD _M and porous silica and talc powder mixture cordierite forming raw material, the collection rate FIG. FIG. 7 is a graph showing the relationship between the ratio A ₁ / A ₂ of the average particle size A ₁ of porous silica and the average particle size A _{2 of} aluminum hydroxide in Experimental Example 2, and the collection rate.

[Embodiment 1]
An embodiment of the exhaust gas purifying filter will be described with reference to FIGS. As illustrated in FIGS. 1 to 3, the exhaust gas purifying filter 1 is formed of, for example, cordierite and has an outer cover 11, partition walls 12, and cells 13. The outer cover 11 is formed, for example, in a cylindrical shape such as a cylindrical shape. In the present embodiment, the axial direction Y of the cylindrical outer cover 11 will be described below as the axial direction Y of the exhaust gas purification filter 1. The arrows in FIG. 2 indicate the flow of the exhaust gas when the exhaust gas purifying filter 1 is disposed in the exhaust gas passage such as an exhaust gas pipe.

  As illustrated in FIGS. 1 and 2, the partition wall 12 partitions the inside of the outer cover 11 into a number of cells. The partition 13 is generally called a cell wall. The partition walls 12 are provided, for example, in a lattice shape. The exhaust gas purifying filter 1 is a porous body, and a large number of pores 121 are formed in the partition wall 12 as illustrated in FIG. Therefore, the exhaust gas purification filter 1 can accumulate and collect PM contained in the exhaust gas on the surface of the partition wall 12 and in the pores 121. PM is a fine particle called particulate matter, particulate matter, particulate, or the like.

  The average pore diameter of the partition walls 12 can be adjusted within a range of 12 μm or more and 30 μm or less, preferably 13 μm or more and 28 μm or less, and more preferably 15 μm or more and 25 μm or less. The porosity of the partition wall 12 can be adjusted in the range of 55% or more and 75% or less, preferably 58% or more and 73% or less, and more preferably 60% or more and 70% or less. When the average pore diameter and the porosity of the partition walls 12 are within these ranges, the required strength is easily ensured while achieving both a high collection rate and a low pressure loss. When the average pore diameter of the partition walls 12 is 12 μm or more and the porosity is 55% or more, the Darcy permeability coefficient can be increased to, for example, 0.8 or more, and the pressure loss can be sufficiently reduced. As a result, the exhaust gas purification filter 1 is suitable for use in, for example, collecting PM discharged from a gasoline engine. When the average pore diameter of the partition walls 12 is 30 μm or less, it is easy to increase the degree of bending of the communication vent holes 122 described later, and the collection rate can be further increased. When the porosity of the partition wall 12 is 75% or less, the structural reliability of the exhaust gas purification filter 1 is easily ensured. The average pore diameter and porosity of the partition wall 12 can be measured by a mercury intrusion method as described later in an experimental example.

  As illustrated in FIGS. 1 and 2, the exhaust gas purification filter 1 has a number of cells 13. The cell 13 is surrounded by the partition wall 12 to form a gas flow path. The extension direction of the cell 13 usually coincides with the axial direction Y.

  As illustrated in FIG. 1, the cell shape in the filter cross section in the direction orthogonal to the axial direction Y is, for example, a square shape, but is not limited thereto. The cell shape may be a polygon such as a triangle, a square, or a hexagon, a circle, or the like. Further, the cell shape may be a combination of two or more different shapes.

  The exhaust gas purification filter 1 is, for example, a columnar body such as a column, and the dimensions thereof can be changed as appropriate. The exhaust gas purification filter 1 has a first end face 14 and a second end face 15 at both ends in the axial direction Y. When the exhaust gas purifying filter 1 is disposed in an exhaust gas path such as an exhaust gas pipe, the first end face 14 becomes an upstream end face, and the second end face 15 becomes a downstream end face.

  The cell 13 can include a first cell 131 and a second cell 132. As illustrated in FIG. 2, the first cell 131 is open at the first end face 14, and is closed at the second end face 15 by the sealing portion 16. The second cell 132 is open at the second end face 15, and is closed at the first end face 14 by the sealing portion 16. The sealing portion 16 can be formed of, for example, a ceramic such as cordierite, but may be formed of another material. In FIG. 2, a plug-shaped sealing portion is formed, but the shape of the sealing portion is not particularly limited as long as the first end face 14 or the second end face 15 can be sealed. Although the illustration of the configuration is omitted, for example, the sealing portion 16 can be formed by partially deforming the partition wall 12 on the first end surface 14 or the second end surface 15. In this case, since the sealing portion 16 is formed by a part of the partition wall 12, the partition wall 12 and the sealing portion 16 are continuously formed.

  The first cells 131 and the second cells 132 are alternately arranged so as to be adjacent to each other in the horizontal direction orthogonal to the axial direction Y and also in the vertical direction orthogonal to both the axial direction Y and the horizontal direction. It is formed. That is, when the first end face 14 or the second end face 15 of the exhaust gas purification filter 1 is viewed from the axial direction Y, the first cells 131 and the second cells 132 are arranged, for example, in a check pattern.

  As illustrated in FIG. 2, the partition wall 12 separates a first cell 131 and a second cell 132 adjacent to each other. As illustrated in FIGS. 3A and 3B, many pores 121 are formed in the partition 12. As illustrated in FIGS. 3A and 3B, the pores 121 in the partition wall 12 are adjacent to each other in addition to the communication vent holes 122 that communicate between the first cell 131 and the second cell 132 adjacent to each other. It may include a non-communicating vent 123 that does not allow communication between the first cell 131 and the second cell 132. FIG. 4 shows the pores 121 of FIG. 3 more simply. Further, in FIGS. 3 and 4, the pores 121 are illustrated in a simplified two-dimensional manner, but it is considered that most of at least the continuous ventilation holes 122 intersect three-dimensionally.

  In the exhaust gas purification filter 1 of the present embodiment, the degree of bending of the continuous ventilation hole 122 is 1.1 or more. The degree of bending is defined by the ratio of the average flow path length L μm of the continuous ventilation hole 122 to the thickness T μm of the partition wall 12. That is, the degree of bending is represented by L / T. When the degree of bending is 1.1 or more, the exhaust gas purification filter 1 can exhibit a high trapping rate even when the porosity is increased. Specifically, the exhaust gas purification filter 1 can exhibit a sufficiently high trapping rate even when the porosity is increased to, for example, 55% or more. Therefore, the trapping rate can be increased while suppressing an increase in pressure loss.

  From the viewpoint of further increasing the collection rate, the degree of bending is preferably 1.15 or more, more preferably 1.2 or more, still more preferably 1.3 or more, and 1.35 or more. Is even more preferred. On the other hand, from the viewpoint that the trapping rate becomes difficult to improve gradually even if the degree of bending is too high, and from the viewpoint of reducing the pressure loss, the degree of bending is preferably 1.6 or less, and 1.5 or less. Is more preferable, and it is more preferable that it is 1.4 or less. In addition, from the viewpoint of achieving a high degree of compatibility between the trapping rate and the pressure loss, the degree of bending is more preferably 1.2 or more and 1.3 or less.

  Here, the degree of bending is obtained as follows. Specifically, as illustrated in FIG. 5, for the measurement sample collected from the exhaust gas purification filter 1, a scan image of the partition wall 12 is taken by CT scanning the partition wall 12. Xradia520 Versa manufactured by ZEISS is used as a CT scanning apparatus. The measurement conditions are a tube voltage of 80 kV and a tube current of 87 mA. The resolution of the captured image is 1.6 μm / pixel. FIG. 5 shows a part of the measurement sample.

  The scan direction S in the CT scan is a direction along the thickness direction of the partition wall 12, and the surface of the partition wall 12 on the side of the first cell 131 which is opened on the first end surface 14 which is the upstream end surface (hereinafter, appropriately referred to as the partition surface 12a). ) To the surface of the partition wall 12 on the second cell 132 side (hereinafter, appropriately referred to as the partition wall back surface 12b) that is open to the second end surface 15 serving as the downstream end surface. 6 and 7 show examples of the scanned image. FIG. 7 is an enlarged view of FIG. 6 and 7, the direction along the axial direction Y is the Y direction, the direction perpendicular to the Y direction and along one of the four partition walls 12 surrounding the second cell 132 is the X direction, and the X direction is the X direction. And the direction perpendicular to the Y direction is the Z direction. Note that the symbol M means the sealing portion 16 on the first end face 14.

  Therefore, the scanning direction S in FIGS. 6 and 7 is the −Z direction. An example of a scanned image in this direction is an upper left image s in FIGS. 6 and 7. The scanned image in the -Z direction is along the XY plane. For reference, a scan image in the Y direction (an image along the XZ plane) is shown at the lower left of FIGS. 6 and 7, and a scan image in the -X direction (an image along the YZ plane) is shown in FIGS. 7 is also shown at the lower right.

  Next, analysis is performed using a group of captured images in the scan direction S (the number of captured images in the scan direction S (= 1.6 μm which is the thickness of the partition wall 12 μm / 1 pixel)). In the following example, the analysis image size has a range of 500 μm × 500 μm in the X and Y planes, and uses the number of the partition walls 12 with a thickness of μm / 1.6 μm in the −Z direction.

  Next, a binarization process is performed on the captured image in the scan direction S. Image analysis software ImageJ (manufactured by the National Institutes of Health (NIH)) is used for the binarization processing. The binarization aims at distinguishing between a pore portion and a skeleton portion in the partition wall 12. The skeleton portion is a ceramic portion in the partition wall 12, and the pore portion is a portion other than the ceramic portion where no ceramic is present. Since the pore portion and the skeleton portion have different luminances, in the binarization process, noise remaining in the captured image is removed, and after an arbitrary threshold is set, the binarization process is performed. Since the threshold value differs depending on each measurement sample, a threshold value at which the pore portion and the skeleton portion can be separated is set for each captured image while visually checking the entire image captured by the CT scan. FIG. 8A shows an example of a photographed image before the binarization processing, and FIG. 8B shows an example of a photographed image after the binarization processing. In FIG. 8B, a black region is a pore portion, and a gray region is a skeleton portion.

  Next, the captured image after the binarization process is read into analysis software GeoDoct (manufactured by SCSK), and a virtual model in which the structure of the pore portion and the skeleton portion is three-dimensionally modeled under the condition of 0.685 μm per Voxel is used. create. Then, with respect to the obtained virtual model, the flow path lengths (μm) of all the continuous ventilation holes 122 are measured. Here, the PM flows along the flow of the gas. The gas tends to flow as the fluid through the shortest flow path in the communication vent hole 122. The flow path whose length is measured as described above is the shortest flow path through which gas flows in the continuous ventilation hole 122. That is, it can be said that the flow path length in the continuous ventilation hole 122 is a parameter that does not always match the length of the line connecting the centers of the hole diameters of the continuous ventilation hole 122. The average value of the channel lengths of all the obtained communication holes 122 is defined as the average channel length L μm of the communication holes 122. The thickness (μm) of the virtual model is the thickness Tμm of the partition 12 when calculating the degree of bending. The bending degree of the measurement sample is calculated by dividing the average flow path length L μm of the continuous ventilation hole 122 obtained as described above by the thickness T μm of the partition wall 12. The degree of bending in the exhaust gas purification filter 1 is calculated from the average value of the degree of bending of each measurement sample obtained as described above for six measurement samples collected from the exhaust gas purification filter 1.

  Note that, specifically, as shown in FIG. 9, the measurement sample includes the central portion 1 a in the axial direction Y passing through the central portion of the diameter of the exhaust gas purification filter 1 and the sealing portion 16 on the first end surface 14 side. The inner portion 1b, the inner portion 1c of the sealing portion 16 on the second end surface 15 side, the central portion 1d in the axial direction Y passing through the center of the radius of the exhaust gas purification filter 1, and the sealing portion on the first end surface 14 side. Samples are taken from six locations, i.e., the immediately inner portion 1e of the sealing member 16 and the immediately inner portion 1f of the sealing portion 16 on the second end surface 15 side. The shape of the measurement sample is a cube whose dimensions in the axial direction Y and the direction perpendicular thereto are 5 mm long × 5 mm wide and the length of the axial direction Y is 5 mm.

  In the exhaust gas purification filter 1, the thickness of the partition wall 12 can be adjusted, for example, in a range of 100 μm or more and 400 μm or less. As shown in FIG. 9, the thickness of the partition wall 12 is the central portion 1a in the axial direction Y passing through the central portion of the diameter of the exhaust gas purification filter 1, and the portion immediately inside the sealing portion 16 on the first end surface 14 side. 1b, the average value of the thickness measurement values measured at three locations of the inner portion 1c immediately inside the sealing portion 16 on the second end surface 15 side.

  The trapping rate generally depends on the frequency of collision of the PM with the partition wall 12. By setting the degree of bending L / T to 1.1 or more as in the present embodiment, the structure of the continuous ventilation hole 122 which becomes a passage for PM becomes complicated. As a result, the frequency of collision of PM in the continuous ventilation hole 122 increases. It is considered that the reason is that the frequency of inertial collision of PM increases due to bending of the continuous ventilation hole 122. As a result, the exhaust gas purification filter 1 exhibits a high trapping rate, and can exhibit a high trapping rate even when the porosity is increased. The relationship between the degree of bending and the collection rate will be described in further detail in Experimental Example 1 described later.

  In the exhaust gas purifying filter 1 of the present embodiment, the trapping rate can be increased to, for example, 70% or more while maintaining the structural strength. The catalyst can be supported by coating the exhaust gas purification filter 1 with a slurry containing a catalyst such as a noble metal. At this time, depending on the catalyst particle diameter, slurry viscosity, supported amount, flow rate conditions of the slurry at the time of coating, etc., a part of the pores 121 is closed and the collection rate is reduced. In particular, the effect of the carried amount is large, and when the carried amount is less than 70 g / L, the trapping rate is reduced to about 4/5 as compared with before carrying, and when the carried amount is 70 g / L or more, the trapping rate is reduced. Tends to decrease to about 2/3 to 1/2 or more. This is because the flow path of the continuous ventilation hole 122 effective for trapping PM is blocked by the catalyst.

  From the viewpoint of responding to the tightening of regulations in the future, it is preferable that the PM collection rate after carrying the catalyst is 60% or more. Therefore, the PM collection rate before carrying the catalyst is preferably 70% or more. Further, from the viewpoint of responding to further tightening of regulations, the PM collection rate before carrying the catalyst is more preferably 80% or more. Further, the exhaust gas purifying filter 1 may have a configuration in which a catalyst is supported by 50 g / L or more, and the degree of bending L / T in a state where the catalyst is supported is 1.6 or more and 2.5 or less. The exhaust gas purification filter 1 is often used in a state where a catalyst is supported, and it is important to maintain the degree of bending of the communication vent 122 of the partition 12 even after the catalyst is supported. The catalyst amount of 50 g / L of the catalyst is a catalyst amount required to satisfy future exhaust gas regulations. According to the above configuration, it is possible to improve the collection rate and suppress the pressure loss even when the catalyst is supported. In addition, the bending degree L / T in a state where the catalyst is supported is also obtained according to the above-described method. The degree of bending in the state where the catalyst is supported is preferably 1.7 or more, more preferably 1.8 or more, and still more preferably 2.0 or more, from the viewpoint of improving the collection rate and suppressing pressure loss. It can be. Further, the degree of bending in a state where the catalyst is supported can be preferably 2.45 or less, more preferably 2.4 or less, and further preferably 2.3 or less. The reason why the degree of bending changes after the catalyst is loaded is that the shortest channel formed before the catalyst loading cannot be obtained because the channel is blocked by the catalyst.

[Embodiment 2]
The exhaust gas purifying filter according to the second embodiment will be described with reference to FIGS. 1 to 9, FIGS. 10 and 11 used in the first embodiment. Note that, among the reference numerals used in the second and subsequent embodiments, the same reference numerals as those used in the above-described embodiments denote the same components and the like as those in the above-described embodiments unless otherwise specified.

In the exhaust gas purifying filter 1 of the present embodiment, the average value Φ ₁ μm of the neck diameter of the continuous ventilation hole 122 and the average pore diameter Φ ₂ μm of the partition wall 12 satisfy the relationship of Expression 3. Incidentally, the average value [Phi ₁ neck diameter, hereinafter appropriately referred to as "average neck diameter [Phi _1". That is, in the exhaust gas purifying filter 1 of the present embodiment, the ratio Φ ₁ / Φ ₂ of the average neck diameter Φ ₁ to the average pore diameter Φ ₂ of the partition wall 12 is 0.2 or more.
Φ ₁ / Φ ₂ ≧ 0.2 Equation 3

  First, the neck diameter will be described. As illustrated in FIG. 10, a large number of pores 121 are formed in the partition wall 12, and a large number of communication vent holes 122 that connect the adjacent cells 13 are present. In the continuous ventilation hole 122, the flow passage area through which the exhaust gas flows is usually not constant, but changes continuously, and there is a narrow portion where the flow passage area is locally reduced. In each communicating hole 122, the smallest narrow portion is the neck portions 124a and 124b.

  FIG. 11 shows a result of performing a CT scan on the partition wall 12 of the exhaust gas purification filter 1 in the same manner as in the first embodiment, and performing a binarization process. In FIG. 11, in the flow path Rt of the continuous ventilation hole 122 indicated by the arrow, the narrowest neck portion 124c is a portion surrounded by a circular frame. The diameter equivalent to the circle of the flow path area of the neck portion is the neck diameter. That is, the diameter of a circle having the same area as the flow path area in the neck is the neck diameter. The neck diameter is defined by the circle-equivalent diameter of the neck portion where the flow passage area of the continuous ventilation hole 122 is minimized. Although the flow path Rt indicated by an arrow in FIG. 11 ends on the side of the scanned image, the flow path Rt actually extends from the partition wall surface 12a to the partition rear surface 12b. Channel.

The neck diameter is measured by a bubble point method. In the bubble point method, first, a porous measurement sample is completely impregnated with a liquid having a known surface tension. Next, pressure is applied to the measurement sample from one end face of the measurement sample. When the pressure is increased, the liquid in the pores of the measurement sample is pushed out, and the gas starts flowing in the measurement sample. The gas flow increases with increasing pressure. The pore diameter (that is, the pore diameter) is calculated from Equation 4 based on the pressure when the gas flows from the end face opposite to the end face to which the pressure is applied. In Equation 4, _Dp is the pore diameter, γ is the surface tension of the liquid to be impregnated, and θ is the contact angle of the liquid, which is a constant. The measuring device used in the present embodiment is CEP-1100AXSHJ manufactured by Porous Material, and Silwick (surface tension: 20.1 [dyne / cm]) is used as a reagent.
D _p = 4 × γ × cos θ × α / P Equation 4

In this embodiment, the measurement sample in the bubble point method is a part of an exhaust gas purification filter. Considering that the measurement sample has a large number of communication holes 122, the pressure at which gas flows out from the end face in the bubble point method is determined by the narrow portions (specifically, neck portions 124a, 124b, 124c) of communication holes 122. Limited. This is because the neck portions 124a, 124b, 124c dominantly determine the gas flow resistance in the continuous ventilation hole 122. Therefore, the pore diameter D _p in Equation 4 is nothing less than the neck diameter.

In the bubble point method, six measurement samples collected from the exhaust gas purification filter 1 are used. The location of each measurement sample is the same as the location of the measurement sample of the degree of bending described in the first embodiment. However, the shape of the measurement sample is a disc-shaped body having a diameter of 19 mm in the direction orthogonal to the axial direction Y and a thickness of 400 to 500 µm along the axial direction Y. In addition, the end surface which changes the pressure is the disk surface of the disk-shaped body. Moreover, the sealing portion 16 is not included in the collected measurement sample. Therefore, the sealing portion 16 is provided in the first cell 131 and the second cell 132 so that the measurement sample has the same gas flow as the exhaust gas purification filter 1. The neck diameter is measured from these six measurement samples by the bubble point method, and the average value is determined. This average value is the average neck diameter [Phi _1. Details will be described later in an experimental example.

The average pore diameter Φ ₂ of the partition wall 12 is determined by a mercury intrusion method as shown in an experimental example described later. The measurement sample is a rectangular parallelepiped in which the size of the exhaust gas purification filter 1 in the direction orthogonal to the axial direction Y is 15 mm long × 15 mm wide and the length in the axial direction Y is 20 mm.

When the average neck diameter Φ ₁ μm and the average pore diameter Φ ₂ μm respectively measured as described above satisfy the relationship of Φ ₁ / Φ ₂ ≧ 0.2, the pressure loss of the exhaust gas purification filter 1 Decrease. From the viewpoint of further reducing the pressure loss, it is more preferable to satisfy the relation Φ ₁ / Φ ₂ ≧ 0.3, more preferably to satisfy the relation _{Φ 1 / Φ 2 ≧ 0.4,} Φ 1 / It is even more preferable that the relationship of Φ ₂ ≧ 0.5 is satisfied.

  Other configurations and operational effects are the same as those of the exhaust gas purification filter 1 of the first embodiment. By combining the configuration of the first embodiment and the configuration of the second embodiment, an exhaust gas purification filter 1 having a high trapping rate and a low pressure loss is provided.

[Embodiment 3]
A method for manufacturing an exhaust gas purifying filter having a degree of bending of 1.1 or more as in Embodiment 1 will be described. The exhaust gas purifying filter of the present embodiment contains cordierite as a main component and is manufactured by performing a mixing step, a forming step, and a firing step as described below.

  In the mixing step, porous silica, talc, and an Al source are mixed. Thereby, a cordierite forming raw material is produced. In the forming step, a kneaded material containing a cordierite forming raw material is prepared, and the kneaded material is formed. Thereby, a molded body is produced. In the firing step, the molded body is fired.

Exhaust gas purification filter 1, for example the chemical composition SiO _2: 45 to 55 wt%, Al ₂ O _3: 33~42 wt%, MgO: a main component from the consisting of cordierite 12-18 wt%. Therefore, in manufacturing the exhaust gas purifying filter 1, a cordierite forming raw material including a Si source, an Al source, and a Mg source is used so that a cordierite composition is generated.

  The cordierite forming raw material is a raw material capable of producing a cordierite composition by firing. As a cordierite forming raw material, a mixture obtained by appropriately mixing silica, talc, aluminum hydroxide, alumina, kaolin and the like is used.

Porous silica having a tap bulk density of 0.38 g / cm ³ or less is used as the silica. By using porous silica having a tap bulk density of 0.38 g / cm ³ or less, the exhaust gas purification filter 1 having a degree of curvature of 1.1 or more can be obtained. The reason is as follows.

  Among cordierite forming raw materials, porous silica and talc are pore forming materials. By using porous silica having a tap bulk density as small as the predetermined value or less, the volume ratio of the pore forming material in the cordierite forming raw material increases. This increases the number of continuous ventilation holes and increases the degree of bending. As a result, an exhaust gas purifying filter 1 having a high trapping rate is obtained. The tap bulk density is a bulk density measured by a method shown in an experimental example described later.

Further increase tortuosity, from the viewpoint of the collection rate is still higher exhaust gas purification filter 1 is obtained, a tap bulk density TD _S of porous silica is preferably at 0.38 g / cm ³ or less, 0.33 g / Cm ³ or less, more preferably 0.28 g / cm ³ or less.

Further, the pressurized bulk density PD _M g / cm ^{3 of} the cordierite forming raw material and the tap bulk density TD _ST g / cm ³ of the mixed powder of porous silica and talc are preferably PD _M / TD _ST ≧ 1. 7, more preferably the relationship of PD _M / TD _ST ≧ 1.8, even more preferably the relationship of PD _M / TD _ST ≧ 1.9 is satisfied. In this case, the degree of bending L / T can be further increased. This is considered to be because the volume of the porous silica and talc in the cordierite forming raw material can be increased by increasing PD _M / TD _ST to the above-mentioned predetermined value or more.

Not only the tap bulk density TD _S of the porous silica but also the press bulk density PD _M g / cm ^{3 of} the cordierite forming raw material and the tap bulk density TD _ST g / cm ³ of the mixed powder of the porous silica and talc By setting the ratio PD _M / TD _ST to the predetermined value or more, the degree of bending can be further increased. Porous silica and talc have different tap bulk densities depending on their particle diameter, surface irregularities, sphericity, etc., and the same applies to cordierite forming raw materials. Is the most important factor in determining Therefore, the PD _M / TD _ST representing the porous silica and the particle number ratio of the talc powder mixture is pore-forming material than to more than the predetermined value, it is possible to enhance more surely tortuosity. The pressurized bulk density is a bulk density measured by a method described in Experimental Example 2 described later.

Further, the average particle diameter A ₂ [mu] m of average particle diameter A ₁ [mu] m and the Al source of porous silica is preferably A ₁ / A ₂ ≦ 3.58, more preferably A ₁ / A ₂ ≦ 3.43, More preferably, the relationship of A ₁ / A ₂ ≦ 3.28 is satisfied. Also in this case, the degree of bending L / T can be further increased. This is because the packing density of each raw material in the cordierite forming raw material can be controlled by adjusting the particle size ratio between the porous silica that is the pore forming material and the Al source that is the skeleton forming material. it is conceivable that. The pore-forming material is a raw material that affects the formation of the pores of the partition walls 12, and a cordierite-forming raw material is, for example, an Si source such as porous silica or talc. On the other hand, the skeleton forming material is a raw material that affects the formation of the ceramic portion of the partition wall 12, and the cordierite forming raw material is, for example, an Al source such as aluminum hydroxide and alumina.

  Further, from the viewpoint that the porosity can be increased, it is preferable to use aluminum hydroxide as the Al source.

  In the production of the exhaust gas purification filter 1, water, a binder, a lubricating oil, a pore former, and the like are appropriately mixed with a cordierite forming raw material to produce a kneaded material containing the cordierite forming raw material. A kneader can be used for mixing. Next, the kneaded material is formed into a honeycomb shape by, for example, extrusion molding. The formed body is made of kneaded clay, and is cut into a predetermined length after drying, for example.

  Next, the molded body is fired. Thus, a sintered body having a honeycomb structure is obtained. Although not shown, the sintered body having the honeycomb structure has the same configuration as the exhaust gas purification filter 1 illustrated in FIGS. 1 and 2 except that the sealing portion is not formed.

  Next, the sealing portion 16 is formed. The sealing portion 16 is formed by filling the first end face 14 or the second end face 15 of the cell 13 with a slurry containing the same type of ceramic raw material as that of the sintered body having the honeycomb structure by using a dispenser, printing, or the like, followed by firing. The method for forming the sealing portion 16 is not particularly limited, and another method may be used. Alternatively, a sealed portion may be formed on the molded body before firing, and sintering of the molded body and the sealed portion may be simultaneously performed in one firing step. In addition, the sealing portion can be formed by deforming a part of the partition wall 12 before or during firing on the end face of the formed body having the honeycomb structure.

  In this way, it is possible to manufacture the exhaust gas purifying filter 1 having the degree of bending of 1.1 or more. Thereby, it is possible to provide the exhaust gas purification filter 1 having a high collection rate.

Further, as in Embodiment 2, in order to increase Φ ₁ / Φ ₂ to a predetermined value or more, the ratio of the number of particles of the pore forming material in the mixed powder may be increased. Thereby, the degree of contact between the pore-forming materials is increased, and Φ ₁ / Φ ₂ can be increased. As a result, the exhaust gas purifying filter 1 with low pressure loss can be obtained without substantially lowering the trapping rate.

In this embodiment, the method of increasing the degree of bending and Φ ₁ / Φ ₂ of the exhaust gas purifying filter 1 containing cordierite as a main component has been described. However, it is based on the principle of the manufacturing method described in this embodiment. For example, the degree of bending and Φ ₁ / Φ ₂ can also be increased for the exhaust gas purification filter 1 mainly composed of a material other than cordierite. For example, other than the cordierite forming raw material, the bulk density and the particle size ratio of the pore forming material and the skeleton forming material can be adjusted in the same manner as in the present embodiment. Thus, it is considered that the exhaust gas purifying filter 1 containing a material other than cordierite as a main component and having a degree of bending or Φ ₁ / Φ _{2 which} is equal to or larger than the predetermined value can be obtained.

[Experimental example 1]
In this example, a plurality of exhaust gas purifying filters 1 having different degrees of bending and Φ ₁ / Φ ₂ are produced, and their PM collection rates are comparatively evaluated.

  Specifically, porous silica, talc, and aluminum hydroxide were appropriately mixed to prepare a cordierite-forming raw material. A pore former made of graphite, water, a lubricating oil, and a binder made of methylcellulose were appropriately added to the cordierite forming raw material to prepare a clay containing the cordierite forming raw material. For the test pieces A1 to A3, A6 to A11, and A14 to A17, the kneading time of the kneaded clay is generally about 30 minutes to 2 hours, but the continuity and the degree of bending due to the improvement in the contact between the particles. The kneading time of the kneaded clay was increased for improvement. However, if the kneading time of the kneaded clay is too long, water evaporates, and sufficient formability cannot be obtained. Therefore, in this experimental example, the kneading time of the kneaded clay is increased by about 1.2 to 1.5 times. did. The kneaded clay produced by these was extruded and fired, and then a sealing portion was formed, thereby producing an exhaust gas purification filter 1 containing cordierite as a main component.

  In this example, 17 types of exhaust gas purifying filters 1 were produced by changing the average particle size and mixing ratio of porous silica, talc, and aluminum hydroxide, the mixing ratio of graphite, and the like. These exhaust gas purifying filters 1 are referred to as test specimens A1 to A6, A8 to A12, and A14 to A19.

The porosity, average pore diameter, degree of bending L / T, and Φ ₁ / Φ ₂ of each specimen were measured, and the results are shown in Table 1. In addition, the collection rate and pressure loss of each specimen were measured, and the results are shown in Table 1. Further, the bending degree L / T and the trapping rate of each test sample after supporting 60 g / L of the catalyst in the pores were measured, and the results are shown in Table 1. For supporting the catalyst, an in-wall coating method is used in which the catalyst-containing slurry is filled up to the inside of the partition wall of each specimen and then the catalyst-containing slurry is sucked from one end face or both end faces of each specimen.

(Porosity, average pore diameter)
The porosity and the average pore diameter Φ ₂ of the partition wall 12 of each specimen were measured by a mercury porosimeter using the principle of the mercury intrusion method. The average pore diameter Φ ₂ is also called an average pore diameter. As a mercury porosimeter, Autopore IV9500 manufactured by Shimadzu Corporation was used. The measurement conditions are as follows.

  First, a test piece for measurement was cut out from each test piece. The test piece is a rectangular parallelepiped having a dimension of 15 mm long × 15 mm wide in a direction perpendicular to the axial direction and a length of 20 mm in the axial direction. Next, the test piece was accommodated in the measurement cell of the mercury porosimeter, and the pressure in the measurement cell was reduced. Thereafter, mercury was introduced into the measurement cell and pressurized, and the pore diameter and pore volume were measured from the pressure at the time of pressurization and the volume of mercury introduced into the pores of the test piece.

The measurement was performed at a pressure of 0.5 to 20,000 psia. Note that 0.5 psia corresponds to 0.35 × 10 ⁻³ kg / mm ² , and 20,000 psia corresponds to 14 kg / mm ² . The range of the pore diameter corresponding to this pressure range is 0.01 to 420 μm. As a constant when calculating the pore diameter from the pressure, a contact angle of 140 ° and a surface tension of 480 dyn / cm were used. The average pore diameter Φ ₂ is the pore diameter at an integrated value of the pore volume of 50%. The porosity was calculated from the following relational expression. The true specific gravity of cordierite is 2.52.
Porosity (%) = total pore volume / (total pore volume + 1 / true specific gravity of cordierite) × 100

(Degree of bending)
The bending degree of the partition wall 12 of each specimen was measured by the method described in the first embodiment. In addition, image analysis software ImageJ version 1.46 manufactured by the National Institutes of Health (NIH) was used for the binarization processing. For the measurement of the flow path length when calculating the degree of bending, the analysis software GeoDoct version 2017 manufactured by SCSK was used.

(Φ ₁ / Φ ₂₎
The average neck diameter [Phi ₁ of communicating pores 122 in each specimen was measured according to the method described in the second embodiment. The bubble point method was performed using a measuring device CEP-1100AXSHJ manufactured by Porous Materials. In the measurement, a ring-shaped jig 4 having an outer diameter of 25.4 mm and an inner diameter of 16.5 mm as illustrated in FIG. 12 was used. The jig 4 is provided with a depression having an inner diameter of 19 mm, and the measurement sample Sp is placed in the depression. The measurement sample Sp was a disc-shaped body having a diameter of 19 mm and a thickness of 400 to 500 μm, and was cut from each specimen as described in the second embodiment. The measurement sample Sp was cut out so that the diameter direction of the disc-shaped body was perpendicular to the axial direction Y of the test body, and the thickness direction of the disc-shaped body was the same as the axial direction Y of the test body. Was. After the surface of the measurement sample Sp cut out from the test body was finish-polished with # 320 sandpaper, a plastic paraffin film having no air permeability was attached to both end surfaces of the measurement sample Sp. By forming a hole in each film, the opening of the first cell 131 and the second cell 132 is formed, and the portion where the hole is desired to be formed is replaced with the sealing portion 16 of the first cell 131 and the second cell 132. And In FIG. 12, the film and the sealing portion 16 are omitted for convenience. The measurement sample Sp provided with the sealing portion 16 was arranged in the depression of the jig 4. As the liquid to be impregnated into the measurement sample Sp in the bubble point method, Silwich manufactured by Porous Materials, whose surface tension was adjusted to 20.1 dynes / cm, was used. This liquid was dropped using a 2 ml syringe until the measurement sample Sp was covered, and vacuum degassing was performed until the liquid was completely impregnated. Thereafter, a pressure was applied with a gas in the thickness direction of the measurement sample Sp, and the relationship between the pressure and the gas flow rate was examined. The direction in which the pressure is applied is the direction of arrow P in FIG. In addition, a first cell 131 is opened on the end surface of the measurement sample Sp where pressure is applied. A second cell 132 is opened on the end surface of the measurement sample Sp opposite to the end surface to which pressure is applied.

FIG. 13 illustrates a pressure curve represented by the relationship between the pressure and the flow rate in the bubble point method. FIG. 13 shows the pressure curves of the test pieces A1 and A2. Further, by measuring the pore diameter (that is, neck diameter) at each pressure from the pressure curve based on Equation 4 of Embodiment 2, the relationship diagram between the neck diameter and the cumulative frequency shown in FIG. 14 is obtained. The neck diameter at a frequency of 50% in this relationship diagram is the neck diameter of the measurement sample Sp. Further, as shown in Embodiment 2, six measurement samples Sp were collected from each test sample, and the neck diameter of each measurement sample Sp was measured. Then, the average value Φ ₁ (that is, the average neck diameter) was determined. Then, to calculate the ratio Φ ₁ / Φ ₂ between the average neck diameter [Phi ₁ and the value [Phi ₂ of the average pore diameter of the above.

(Collection rate, pressure drop)
Specifically, the PM collection rate and the pressure loss were measured as follows. The exhaust gas purifying filter 1 of each test body was attached to the exhaust pipe of a gasoline direct injection engine, and exhaust gas containing PM was passed through the exhaust gas purifying filter 1. At this time, the PM number in the exhaust gas before flowing into the exhaust gas purification filter 1 and the PM number in the exhaust gas flowing out from the exhaust gas purification filter 1 were measured, and the PM collection rate was calculated. The measurement conditions are a temperature of 450 ° C. and an exhaust gas flow rate of 2.8 m ³ / min. The pressure loss was measured by measuring the pressure before the exhaust gas purification filter and the pressure after the exhaust gas purification filter using a pressure sensor at the same time as the measurement of the trapping rate, and measuring the difference as a pressure loss. The measurement conditions were a temperature of 720 ° C. and an exhaust gas flow rate of 11.0 m ³ / min. Each measurement was performed in an initial state where PM was not deposited in the exhaust gas purification filter. The PM number was measured using a PM particle number counter (AVL-489) manufactured by AVL.

  As known from Table 1, the exhaust gas purification filter 1 having a degree of curvature of 1.1 or more has a high trapping rate. FIG. 15 shows the relationship between the degree of bending of the specimen and the collection rate in order to know the tendency of the relationship between the degree of bending and the collection rate. As is known from FIG. 15, when the degree of bending is increased, the collection rate is increased, and when the degree of bending is 1.1 or more, a high collection rate exceeding 65% is exhibited. When the degree of bending is 1.2 or more, the collection rate exceeds 70%. This is considered to be because as the bending degree is increased and the flow path of the continuous ventilation hole in the partition wall becomes more complicated, the frequency of the wall collision due to the Brownian motion increases, and the frequency of the inertial collision of the PM also increases.

  On the other hand, when the degree of bending exceeds 1.6, the rate of increase in the collection rate is significantly reduced. The reason is that the more complicated the flow path of the continuous vent, the more intersections between the flow paths actually increase, and the frequency of wall collisions due to Brownian motion increases. It is considered that this is because the collision caused by inertia of the PM is reduced by the increase. In addition, as shown in FIG. 16, there is a proportional relationship between the degree of bending and the pressure loss, and as the degree of bending increases, the pressure loss increases. Accordingly, it can be seen that the degree of bending is preferably 1.6 or less from the viewpoint that the effect of improving the collection rate is hardly obtained and the pressure loss increases.

Also, as is known from Table 1, when the average neck diameter Φ ₁ / average pore diameter Φ ₂ increases, the pressure loss decreases without substantially lowering the trapping rate. FIG. 17 shows the relationship between Φ ₁ / Φ ₂ and the collection rate of the test specimen in order to know the relationship between Φ ₁ / Φ ₂ and the collection rate, and the relationship between Φ ₁ / Φ ₂ and the pressure loss. , Φ ₁ / Φ ₂ and the pressure loss are shown in FIG.

As is known from FIGS. 17 and 18, when Φ ₁ / Φ ₂ is increased, the pressure loss can be reduced without substantially changing the collection rate. In particular, by setting Φ ₁ / Φ ₂ to 0.2 or more, the pressure loss can be significantly reduced without substantially changing the trapping rate. In general, a technique of increasing the average pore diameter is used to suppress the pressure loss. However, in the continuous vent hole, the enlargement of a neck portion serving as a bottleneck is particularly effective. In other words, it is effective to increase the average neck diameter Φ ₁ / average pore diameter Φ ₂ to reduce the pressure loss. In particular, by setting Φ ₁ / Φ ₂ to 0.2 or more, the remarkable reduction effect of the pressure loss can be obtained. can get.

Furthermore, by setting Φ ₁ / Φ ₂ to 0.2 or more while maintaining the degree of bending to 1.1 or more, a high collection rate and a low pressure loss, which tend to be in a trade-off relationship with each other, are achieved at a high level. Can be done.

In this example, the relationship between the channel shape factor such as the degree of bending and Φ ₁ / Φ ₂ and the collection rate and pressure loss is shown, and the same applies to the exhaust gas purification filter 1 made of a material other than cordierite. I can say that. That is, in addition to cordierite, the exhaust gas purifying filter 1 made of a material such as aluminosilicate mainly composed of SiC, ceria, zirconia, and mullite also has the bending degree and Φ ₁ / Φ ₂ as in this example. The same effect can be obtained by adjusting to.

[Experimental example 2]
In this example, a method of manufacturing an exhaust gas purifying filter having a high degree of bending will be discussed. When the exhaust gas purification filter 1 contains cordierite as a main component, a cordierite forming raw material including a Si source, an Al source, and a Mg source is used so that a cordierite composition is generated. As a cordierite forming raw material, a mixture obtained by appropriately mixing porous silica, talc, aluminum hydroxide, alumina, kaolin, and the like can be used. In the production of the exhaust gas purifying filter 1, water, a binder, a lubricating oil, a pore former, and the like are appropriately mixed with a cordierite forming raw material, and a clay containing the cordierite forming raw material can be prepared. Then, as shown in Experimental Example 1, the exhaust gas purification filter 1 can be obtained by performing processes such as extrusion molding, firing, and forming a sealing portion of the clay.

  Porous silica and talc can be called pore-forming materials because they can be melted at a high temperature to form the pores 121. It is considered that the higher the particle number ratio of the pore-forming material, the higher the contact between the particles and, as a result, the higher the degree of bending. Therefore, in order to increase the degree of bending, when extruding the kneaded clay containing the cordierite forming raw material, the number ratio of the particles of porous silica and talc contained in the kneaded clay may be controlled.

  However, it is assumed that the particle number ratio is difficult to measure, and that the measured value varies depending on the molding conditions. Therefore, an index that can adjust the degree of bending by controlling the conditions of the raw material powder such as silica, talc, and Al source is desired. From such a viewpoint, the following examination was conducted by focusing on the tap bulk density of the porous silica, the pressurized bulk density of the powder of the cordierite forming raw material, and the like.

  Specifically, a clay having the composition shown in Table 2 is considered. Here, as shown in Table 2, by appropriately mixing porous silica, talc, and aluminum hydroxide, the cordierite forming raw material is adjusted. As the porous silica, three types of silica having different tap bulk densities are used. The tap bulk densities of these porous silicas are shown in Table 3. The tap bulk density is measured as follows.

(Tap bulk density)
The measurement of the tap bulk density is performed by a tap bulk density method fluid adhesion measuring instrument. Specifically, a tap densa manufactured by Seishin Enterprise was used. The powder to be measured was filled in a cylinder of the measuring instrument, the powder to be measured was compressed by tapping, and the bulk density was calculated from the mass of the powder to be measured in a compressed state and the volume of the cylinder. This bulk density is the tap bulk density. Porous silica or a mixed powder of porous silica and talc was used as the powder to be measured.

  As the aluminum hydroxide, one type or two types having different average particle diameters are used. To the cordierite forming raw material, a pore former made of graphite, water, a lubricating oil, and a binder made of methylcellulose are appropriately added. The production of kneaded clay from such a mixed raw material will be considered. For the test pieces B14 and B15, the kneading time of the kneaded clay is generally about 30 minutes to 2 hours, whereas the kneading time is about 30 minutes to 2 hours. Kneading time was increased. However, if the kneading time of the kneaded clay is too long, water evaporates, and sufficient formability cannot be obtained. Therefore, in this experimental example, the kneading time of the kneaded clay is increased by about 1.2 to 1.5 times. did.

  On the other hand, in order to examine an evaluation method simulating kneaded clay, the pressure bulk density of a powder of a cordierite forming raw material (hereinafter, referred to as a mixed powder) was measured. Specifically, first, the mixed powder was put into a measuring device having a diameter of 25 mm and a length of 20 mm in a pressure measuring device “Autograph” manufactured by Shimadzu Corporation, and pressurization of the mixed powder was started. The pressing speed is 1 mm / min. When the load reached 7 kN corresponding to the actual molding pressure of 15 MPa, pressurization was stopped by limit control. By this pressing, a columnar pellet made of the mixed powder is obtained. The weight and height of the pellet were measured.

  The height of the pellet can be measured by a caliper, a micrometer, a three-dimensional measuring device, or the like. Here, the measurement was performed using a micrometer. Since the diameter of the pellet was 25 mm, the volume of the pellet was calculated from the product of the diameter and the height.

  The density was calculated from the volume and weight of the pellet. Density is calculated by dividing weight by volume. This density was defined as the bulk density under pressure. It should be noted that methyl cellulose “65MP-4000” manufactured by Matsumoto Yushi Seiyaku Co., Ltd. was added as a binder to the mixed powder. The binder is for facilitating the handling of the pellet-shaped mixed powder, and other binders can be used. Specifically, a total of 2 g of 1.5 g of the mixed powder and 0.5 g of the binder is used.

  In general, there is a correlation between the particle diameter and the bulk density, and the smaller the particle diameter, the more space is formed between the particles, and thus the smaller the bulk density. As for the number of particles arranged in a certain volume, the smaller the particle diameter, the larger the number of particles. Therefore, the number of particles increases as the bulk density decreases. That is, the bulk density and the number of particles are in inverse proportion.

Particle number ratio R of the pore-forming material in the mixed powder, the porous silica and talc particle number N _ST, the particle number N _M of all the ingredients mixed powder used for manufacturing the exhaust gas purification filter 1, the following formula It is calculated by (i). Here, the pore-forming materials are porous silica and talc.
R = N _ST / N _M (i)

When the relationship between the bulk density and the number of particles described above is applied to the formula (i), the particle number ratio R of the pore-forming material is determined by all the raw materials, that is, the raw material mixed powder of porous silica, talc, and aluminum hydroxide. a bulk density D _M of the a bulk density D _ST porous silica and talc mixed powder is expressed by the following equation (ii).
R = D _M / D _ST (ii)

In other words, from the formula (ii), it can be said that by increasing the bulk density of aluminum hydroxide and decreasing the bulk density of porous silica or talc, the number ratio of particles is increased. In this example, the bulk density D _S of the porous silica, with a tapped bulk density TD _S of the porous silica, as the bulk density D _ST porous silica and talc mixed powder, mixing of porous silica and talc using the tap bulk density TD _ST powder, the bulk density D _M of cordierite forming raw material, using a pressurized圧嵩density PD _M cordierite forming raw material.

For each clay shown in Table 2, were tapped bulk density TD _S of porous silica, tapped bulk density TD _ST porous silica and talc mixed powder, the pressurized圧嵩density PD _M cordierite forming raw material was measured. Tapped bulk density TD _S, pressurized圧嵩density PD _M is measured by the method described above. Table 3 shows the results.

Extrusion molding, sintering, and formation of a sealing portion were performed using each of the clays shown in Table 2 in the same manner as in Experimental Example 1 to obtain an exhaust gas purification filter 1 of each test body. The bending degree L / T, average neck diameter Φ ₁ / average pore diameter Φ ₂ , collection rate, and pressure loss of each specimen were measured in the same manner as in Experimental Example 1. Table 3 shows the results. Note that the test pieces B1, B5, B14, and B15 are the same exhaust gas purification filters 1 as the test pieces A1, A5, A14, and A15 of Experimental Example 1. The test body B13 is the exhaust gas purification filter 1 manufactured in the present example and having a degree of curvature of 1.12.

As known from Table 3, small porous silica B with tapped bulk density TD _S, by using a porous silica C, a pressure圧嵩density PD _M cordierite forming raw material, porous silica and mixed powder of talc The ratio of the number of particles of porous silica and talc, which is represented by the ratio PD _M / TD _ST to the tap bulk density TD _ST , becomes large. In addition, by using a mixture of aluminum hydroxide particles having a relatively large average particle diameter and aluminum hydroxide having a relatively small average particle diameter, the bulk density of aluminum hydroxide is increased and the filling property is improved. Can be.

  In general, by setting the ratio of small particle size aluminum hydroxide having a small average particle size to the total amount of aluminum hydroxide to 25 to 30 wt%, the filling property is further improved. However, the optimum compounding ratio for improving the filling property varies depending on the combination of the particle diameters, the particle shape, the distribution, and the like.

  In the present experimental example, as shown in Tables 2 and 3, in specimens B5 and B13, aluminum hydroxide having an average particle diameter of 5 μm was used alone as aluminum hydroxide, and in specimens B1 and B14, small particle diameter was used. And aluminum hydroxide having a large particle diameter of 3: 7 (small particle diameter: large particle diameter) was used. In the test body B15, aluminum hydroxide having a small particle diameter and a large particle diameter of 5: 5 was used. As a result, as shown in Table 3, when the compounding ratio of the small particle diameter is 30 to 50 wt%, the bulk density of the cordierite forming raw material is substantially the same.

Moreover, as known from Table 3, the pressurized圧嵩density PD _M cordierite forming raw material, the ratio PD _M / TD _ST of the tap bulk density TD _ST porous silica and talc mixed powder is pore-forming material Of the specimens B5 and B13, specimens B1 and B15, and specimen B14 in this order. The order of the PD _M / TD _ST is substantially correlated with the order of the degree of curvature L / T and the order of the collection rate. Therefore, it can be seen that the tapping density of the porous silica should be reduced and the ratio PD _M / TD _ST should be increased in order to increase the degree of bending and the collection rate.

Figure 19 shows the relationship between the tap bulk density TD _S and the collection rate of the porous silica. FIG. 20 shows the relationship between the PD _M / TD _ST and the collection rate. Further, in FIG. 21 shows the relationship between the ratio A ₁ / A ₂ and the collection rate of the average particle diameter A ₁ of the porous silica with an average particle diameter A ₂ of the aluminum hydroxide.

As is known from FIG. 19, it is understood that the trapping rate can be increased to 70% or more by using porous silica having a tap bulk density of 0.38 g / cm ³ or less. Further, as is known from FIG. 20, it is understood that the trapping rate can be increased to 70% or more by setting the ratio of PD _M / TD _ST to 1.7 or more. Further, as is known from FIG. 21, it is understood that the trapping rate can be increased to 70% or more by setting A ₁ / A ₂ to 3.58 or less.

  In this example, silica, talc, and alumina hydroxide were used as cordierite forming raw materials, but cordierite forming raw materials can include raw materials such as kaolin and alumina. When the porosity may be reduced, alumina can be used as the Al source. As the Al source, at least one of aluminum hydroxide and alumina can be used. Aluminum hydroxide and alumina may have the same average particle diameter or different average particle diameters. These combinations can be appropriately adjusted from the viewpoints of moldability, shrinkage, cost, and the like.

  The present invention is not limited to the above embodiments and experimental examples, and various changes can be made without departing from the gist of the invention. In addition, each configuration shown in each embodiment and each experimental example can be arbitrarily combined.

DESCRIPTION OF SYMBOLS 1 Exhaust gas purification filter 11 Outer skin 12 Partition wall 13 Cell 122 Continuous vent

Claims (9)

Outer skin (11),
A porous partition (12) that partitions the inside of the outer skin into a plurality of cells (13);
The partition has a plurality of communicating holes (122) for communicating between the cells adjacent to the partition,
An exhaust gas purifying filter (1), wherein a degree of flexure L / T defined by a ratio of an average flow path length Lμm of the communicating holes to a thickness Tμm of the partition wall satisfies the relationship of the following formula 1.
L / T ≧ 1.1 Expression 1 The exhaust gas purification filter according to claim 1, wherein the degree of bending L / T further satisfies a relationship represented by the following expression 2.
L / T ≦ 1.6 Expression 2 The average value Φ ₁ μm of the neck diameter defined by the equivalent circle diameter of the neck portion where the flow passage area of the continuous ventilation hole is minimized, and the average pore diameter Φ ₂ μm of the partition wall satisfy the following formula 3. The exhaust gas purifying filter according to claim 1 or 2.
Φ ₁ / Φ ₂ ≧ 0.2 Equation 3   The exhaust gas purification filter according to any one of claims 1 to 3, wherein the partition walls have a porosity of 55 to 75% and an average pore diameter of 12 to 30 m.   The exhaust gas purification filter according to any one of claims 1 to 4, wherein the particulate matter collection rate of the exhaust gas purification filter is 70% or more. The catalyst is supported by 50 g / L or more,
The exhaust gas purification filter according to any one of claims 1 to 5, wherein the degree of curvature L / T in a state where the catalyst is supported is 1.6 or more and 2.5 or less. A method for producing an exhaust gas purification filter (1),
A mixing step of preparing a cordierite forming raw material by mixing porous silica having a tap bulk density of 0.38 g / cm ³ or less, talc, and an Al source;
Forming a kneaded clay containing the cordierite forming raw material, a forming step of forming a molded body by forming the kneaded clay,
A method for producing an exhaust gas purifying filter, comprising: a firing step of firing the molded body. In the mixing step, the pressure圧嵩density PD _M g / cm ³ of the cordierite forming raw material, a tapped bulk density TD _ST g / cm ³ in the mixed powder of the porous silica and the talc, PD _M / The method for producing an exhaust gas purifying filter according to claim 7, wherein a cordierite-forming raw material that satisfies the relationship of TD _ST ≧ 1.7 is produced. The porous average particle diameter A ₁ [mu] m silica and an average particle diameter A ₂ [mu] m of the Al source is satisfy the relation of A ₁ / A ₂ ≦ 3.58, purification of exhaust gas according to claim 7 or 8 Manufacturing method of filter.