JP2017141778A - Inorganic particle carrying honeycomb filter and manufacturing method of inorganic particle carrying honeycomb filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inorganic particle carrying honeycomb filter which hardly raises a pressure loss even when particles such as soot are accumulated and can catch the particles such as soot high efficiently, and its manufacturing method.SOLUTION: A honeycomb filter includes: a porous honeycomb structural bodies 120 having a plurality of channels 110a, 110b; a plurality of sealing parts which close one end of a part of channels of the plurality of channels and the other end of the remaining parts of the plurality of channels; and an inorganic particle layer M3 carried by the honeycomb structural bodies 120. In the inorganic particle carrying honeycomb filter, when a total length of parts which are not brought into contact with the honeycomb structural bodies 120 within a contour line CL of the inorganic particle layer M3 is a[μm] in a cross-section photograph of the honeycomb structural body 120 and a total area of the inorganic particle layer M3 is b[μm] in the cross-section photograph, a/b is 0.15 to 0.3[1/μm].SELECTED DRAWING: Figure 5

Description

  The present invention relates to an inorganic particle-supporting honeycomb filter and a method for manufacturing an inorganic particle-supporting honeycomb filter.

  Conventionally, an inorganic particle-supporting honeycomb filter having a porous honeycomb filter and inorganic particles as a catalyst supported on the filter is known. The catalyst promotes soot combustion, NOx treatment, and the like.

JP 2007-130637 A JP 2009-273916 A JP-A-8-332329 JP 2009-663 A JP 2009-72693 A

  However, when inorganic particles are supported on the honeycomb filter, there is a problem that pressure loss tends to increase when particles such as soot accumulate on the filter. Further, based on this, it is conceivable to increase the porosity of the honeycomb filter in advance, but in that case, there arises a problem that particles such as soot cannot be sufficiently collected and are easily passed.

  The present invention has been made in view of the above problems, and an inorganic particle-supporting honeycomb filter that can hardly collect pressure particles even when particles such as soot accumulate and can collect particles such as soot with high efficiency, and production thereof. It aims to provide a method.

An inorganic particle-carrying honeycomb filter according to the present invention includes a porous honeycomb structure having a plurality of flow paths, one end of a part of the plurality of flow paths, and the inside of the plurality of flow paths. A plurality of sealing portions for closing the other end of the remaining flow path, and an inorganic particle layer supported on the honeycomb structure. Then, in the cross section of the honeycomb structure, a [μm] is the total length of the portion of the contour line of the inorganic particle layer that is not in contact with the honeycomb structure, and in the cross section is the total area of the inorganic particle layer. When b [μm ² ] is set, a / b is 0.15 to 0.3 [1 / μm].

  The inorganic particle-supporting honeycomb filter according to the present invention has a / b sufficiently higher than that of the conventional filter. A high a / b means that there are many inorganic particle layers formed in layers along the inner walls of the pores so as to leave some pore voids without blocking the pores. As a result, even after the inorganic particles are supported, even if the gas easily passes through the pores and the soot accumulates, the pressure loss does not easily increase. Even if the porosity of the honeycomb structure before supporting the inorganic particle layer is large, the pores are appropriately narrowed by the inorganic particle layer, so that the trapping efficiency of soot is increased.

Here, the porosity of the inorganic particle layer may be 47 to 65%.
According to this, since a gap is formed between the inorganic particles in the inorganic particle layer, the catalyst can be effectively used.

  The porosity of the honeycomb structure may be 40 to 75%. Such a porosity has a high effect.

The total volume of inorganic particles per apparent unit volume of the honeycomb structure may be ^{30 to} 110 cm ³ / L.

A method for manufacturing an inorganic particle-supporting honeycomb filter according to the present invention includes impregnating a honeycomb filter with a mixture containing a dispersion medium, thermoplastic resin particles, and inorganic particles;
Removing the dispersion medium from the mixture impregnated in the honeycomb filter to obtain a particle-attached honeycomb filter;
Heating the particle-adhered honeycomb filter to remove the thermoplastic resin component by thermal decomposition and / or combustion.

  According to the present invention, first, a porous material containing inorganic particles and thermoplastic resin particles is formed in the honeycomb structure by impregnation and solvent removal. This porous material is formed so as to close most pores of the honeycomb structure. Next, in the heating step, it is considered that the thermoplastic resin particles in the porous material are first melted and flowed by heating the honeycomb structure to which the porous material is adhered (that is, the particle-adhered honeycomb filter). A thin thermoplastic resin layer containing inorganic particles is formed along the surface of the honeycomb structure. Unlike the porous material before flow, the thermoplastic resin layer has a dense structure rather than a porous material, so the apparent volume is reduced, and the remaining space in which no thermoplastic resin layer exists in the pores of the honeycomb structure Is secured. When the temperature rises further in the heating step, the thermoplastic resin is removed from the thermoplastic resin layer containing inorganic particles by thermal decomposition and / or combustion, and the inorganic space is left along the pore walls while leaving the remaining space. A particle layer is formed. Furthermore, in this heating step, since the thermoplastic resin is removed from the thermoplastic resin layer containing inorganic particles, it is possible to provide an appropriate gap between the inorganic particles in the inorganic particle layer.

  Here, the average particle diameter D50 of the thermoplastic resin particles may be 0.1 to 10 μm.

  The resin of the thermoplastic resin particles may include an ethylene vinyl acetate resin.

  Furthermore, the average particle diameter D50 of the inorganic particles may be 0.1 to 10 μm.

  In the said method of this invention, it is preferable that ratio of the average particle diameter of the said thermoplastic resin particle and the average particle diameter of the said inorganic particle is 0.1-10. Thus, when the thermoplastic resin particles and the inorganic particles are close in particle size, when the thermoplastic resin melts and flows in the initial stage of the heating step, the thermoplastic resin is accompanied by the inorganic particles. Since it is thought that it will flow easily, it is suitable for manufacture of the inorganic particle carrying | support honeycomb filter of this invention.

  ADVANTAGE OF THE INVENTION According to this invention, even if particles, such as soot, accumulate, a pressure loss does not become high easily, and the inorganic particle carrying | support honeycomb filter which can collect particles, such as soot, with high efficiency, and its manufacturing method are provided.

FIG. 1 is a schematic cross-sectional view of an inorganic particle-supporting honeycomb filter. FIG. 2 is an enlarged view of the honeycomb filter of FIG. 3 (a) and 3 (b) are schematic cross-sectional views showing a method for manufacturing the inorganic particle-supporting honeycomb filter of FIG. FIG. 4 is an example of a cross-sectional SEM photograph of the honeycomb structure after impregnation and drying in Example 1. (Magnification: 1500 times) 5A and 5B are examples of cross-sectional SEM photographs of the honeycomb structure of the inorganic particle-supporting honeycomb filter after heating and thermal decomposition / combustion in Example 1. FIG. ((A) magnification 1500 times, (b) magnification 150 times) FIG. 6 is an example of a cross-sectional SEM photograph of a honeycomb structure of an inorganic particle-supporting honeycomb filter after heating and pyrolysis / combustion in Comparative Example 1. ((A) magnification 1500 times, (b) magnification 150 times) FIG. 7 is a cross-sectional SEM photograph used for image analysis of the honeycomb structure of the inorganic particle-supporting honeycomb filter after heating and pyrolysis / combustion in Example 1. (Magnification: 150 times) FIG. 8 is an image obtained by extracting only the honeycomb structure portion as black and obtaining the other portion as white from the cross-sectional SEM photograph of FIG. 7, and subsequently performing expansion processing of the black portion for one outer pixel. This is an example of the image A. FIG. 9 shows an image B obtained by extracting only the portion of the inorganic particle layer M3 from the cross-sectional SEM photograph of FIG. 7, extracting the contour line of the inorganic particle layer M3, and expressing the contour line in white on a black background. It is an example. FIG. 10 is an example of an image C obtained by superimposing the image A and the image B with a transmittance of 50%. FIG. 11A is an enlarged cross-sectional SEM photograph of the inorganic particle layer of Example 1, and FIG. 11B is an enlarged cross-sectional SEM photograph of the inorganic particle layer of Comparative Example 1. FIG. 12 is an example of a cross-sectional SEM photograph of a honeycomb structure of an inorganic particle-supporting honeycomb filter after heating and pyrolysis / combustion in Comparative Example 2. ((A) magnification 1500 times, (b) magnification 150 times)

  Embodiments of the present invention will be described with reference to the drawings.

(Inorganic particle supporting honeycomb filter)
As shown in FIG. 1, the inorganic particle-supporting honeycomb filter 200 includes a porous honeycomb structure 120, a plurality of sealing portions 130, and an inorganic particle layer (not shown in FIG. 1) supported on the honeycomb structure 120. Have. Here, the porous honeycomb structure 120 and the plurality of sealing portions 130 are referred to as a honeycomb filter 100.

  The honeycomb structure 120 has a column shape, and has an inlet end face (one end face) 100a and an outlet end face (the other end face) 100b. The outer shape of the honeycomb structure 120 can be, for example, a cylinder, a prism, or an elliptic cylinder.

  The honeycomb structure 120 has a plurality of inlet channels 110a and a plurality of outlet channels 110b. The cross-sectional shapes of the inlet channel 110a and the outlet channel 110b can be, for example, a circle, an ellipse, a quadrangle, a hexagon, and an octagon. The honeycomb structure 120 functions as a partition that separates the inlet channel 110a and the outlet channel 110b adjacent to each other.

  Each inlet channel 110a is opened at the inlet end surface 100a and sealed by the sealing portion 130 at the outlet end surface 100b. Each outlet channel 110b is opened at the outlet end surface 100b and sealed by the sealing portion 130 at the inlet end surface 100a. In FIG. 1, the sealing portion 130 has a plug shape, but the sealing portion 130 may be formed by deforming a part of the honeycomb structure 120 (for example, a conical shape portion). The sealing part 130 may be porous, but may be non-porous.

  The material of the honeycomb structure 120 and the sealing portion 130 is ceramic. Examples of the ceramic are an aluminum titanate ceramic, a silicon carbide ceramic, and a cordierite ceramic. The aluminum titanate-based ceramic can contain magnesium, silicon, and the like. The ceramic may contain trace components derived from raw materials or trace components inevitably contained in the production process.

  The porosity of the honeycomb structure 120 (calculated on the assumption that an inorganic particle layer described later is also part of the void) can be 40 to 75%. The porosity is preferably 55 to 70% and more preferably 55 to 65% in maintaining the pressure loss performance and improving the catalyst activity. If the porosity exceeds 75%, the strength of the honeycomb structure 120 may decrease. The porosity can be obtained by image analysis of the cross-sectional SEM image. Specifically, a cross-sectional SEM image of the partition wall is acquired (magnification 150 times), and the pore portion (void) of the cross-sectional SEM image and the base material portion are separated using image analysis software (for example, ImageJ). A binarization process is performed to extract only the pores. For this extracted image, an analysis region is set so that one side substantially includes the thickness direction of the partition and the other side is about twice the thickness direction, and the porosity is measured from the area ratio of the pores in this analysis region. be able to.

  The average pore diameter (the inorganic particle layer is also considered to be part of the pores) in the honeycomb structure 120 can be 10 to 30 μm. The average pore diameter can be calculated by image analysis using a cross-sectional SEM image. Specifically, a cross-sectional SEM image of the partition wall is acquired (magnification 150 times), and the pore portion (void) of the cross-sectional SEM image and the base material portion are separated using image analysis software (for example, ImageJ). A binarization process is performed to extract only the pores. An average pore diameter can be measured by performing a Watershed (region division) process on the extracted image and obtaining a median value in the major axis distribution of the ellipse when the divided pores are approximated to an ellipse. The median means a numerical value at the center when the major axis is arranged in order from the smallest.

The density of the flow path in the honeycomb structure 120, that is, the cell density can be set to 35 to 80 cells / cm ² , for example.

  In such a honeycomb filter, a green honeycomb structure is formed from a raw material including a ceramic source and a pore former, and then one end or the other end of each flow path is sealed to form a sealed portion, and then fired. Is obtained.

(Inorganic particle layer)
FIG. 2 is an enlarged schematic view of the cross section of the honeycomb structure 120, showing the pores P and the surfaces of the inlet channel 110a / outlet channel 110b. An inorganic particle layer M <b> 3 is provided on the surface of the honeycomb structure 120. Examples of the surface of the honeycomb structure 120 include the inner surfaces of the pores P of the honeycomb structure 120 and the inner surfaces of the inlet channel 110a and the outlet channel 110b of the honeycomb structure 120.

  The inorganic particle layer M3 is composed of a large number of inorganic particles.

The inorganic particles are not particularly limited as long as they are inorganic particles that can function as a catalyst or a catalyst carrier. Examples of inorganic particles include alumina particles, silica particles, magnesia particles, titania particles, zirconia particles, ceria particles, La ₂ O ₃ particles, BaO particles, zeolite particles and other inorganic oxides, or one or more of these It is a complex oxide containing.

  These inorganic particles may carry fine particles of at least one metal element selected from the group consisting of Pt, Pd, Rh, silver, vanadium, chromium, manganese, iron, cobalt, nickel, and copper. In the pores P of the honeycomb structure 120, there is a remaining space P2, which is a space where no inorganic particles exist.

  The average particle diameter D50 of the inorganic particles can be 0.1 to 10 μm. The average particle diameter D50 can be 1 μm or more, and can also be 3 μm or less. The average particle diameter D50 can be the median value of the constant direction diameter (Feret tangential diameter) distribution of the cross-sectional SEM photograph. The median means a numerical value at the center when the major axis is arranged in order from the smallest. Specifically, a cross-sectional SEM image of the inorganic particle layer in the partition wall is acquired (magnification 2000 times), and an image obtained by extracting the inorganic particles by binarization processing is acquired using image analysis software (for example, ImageJ). For the extracted inorganic particles, the average particle diameter D50 of the inorganic particles can be measured by obtaining the Feret tangent diameter and obtaining the median thereof. The median means a numerical value at the center when the Feret tangent diameters are arranged in order from the smallest.

In the present embodiment, the inorganic particle layer M3 is formed along the inner surfaces of the pores P of the honeycomb structure 120 and the inner surfaces of the flow paths 110a and 110b. The thickness of the inorganic particle layer M3 can be set to 2 μm to 30 μm, for example.
In the pores P of the honeycomb structure 120, a remaining space P2 is left in addition to the inorganic particle layer M3. In the cross section, the proportion of the remaining space in the pores P can be 10 to 45%.

In the cross section of the honeycomb structure 120, a portion of the contour line CL of the inorganic particle layer M3 that is not in contact with the honeycomb structure 120, that is, a portion that is in contact with the remaining space P2 or the inlet channel 110a and the outlet channel 110b. When the total length is a [μm] and the total area of the inorganic particle layer M3 is b [μm ² ] in the cross section, a / b is 0.15 to 0.3 [1 / μm].
Measurement of a and b can be performed based on a cross-sectional SEM image of the inorganic particle-supporting honeycomb filter 200 with a magnification of about 150 times. Usually, since the contrast is different between the honeycomb structure 120 and the inorganic particle layer M3, the outline CL of the inorganic particle layer M3 and a portion of the outline CL that is not in contact with the honeycomb structure 120 can be easily formed. Can be extracted. The range in which a and b are measured can be, for example, a quadrangle with sides of about 200 to 700 μm. The range may not include the inlet channel 110a and the outlet channel 110b, but may include them.

  The porosity of the inorganic particle layer M3 may be 47 to 65%.

Further, the total volume of inorganic particles per apparent unit volume of the honeycomb structure 120 may be ³⁰ to 110 cm ³ / L.

According to the inorganic particle-supporting honeycomb filter according to the present embodiment, a / b is sufficiently large, that is, the honeycomb structure 120 is formed in layers so as to form the remaining space P2 without closing the pores P of the honeycomb structure 120. There are many inorganic particle layers M3. Thereby, even after the inorganic particles are supported, the gas easily flows through the pores P, and even if soot is accumulated, the pressure loss is not easily increased. Even if the porosity of the honeycomb structure 120 before supporting the inorganic particles is large, the pores P of the honeycomb structure are appropriately narrowed by the inorganic particle layer M3, so that the collection efficiency of particles such as soot is high. Become.
Moreover, when the porosity in the inorganic particle layer M3 is high, the utilization efficiency of the catalyst increases.

  On the other hand, in the conventional inorganic particle-carrying honeycomb filter, a / b is less than 0.15, that is, the inorganic particles are partially and uniformly supported so as to fill the pores P, so that gas can flow. When the pores are reduced and particles such as soot accumulate, the pressure loss tends to increase. Moreover, since many pores whose channels are not narrowed by the inorganic particles remain, the collection efficiency of particles such as soot is not increased.

(Inorganic particle-supporting honeycomb filter manufacturing method)
Then, an example of a suitable manufacturing method of such an inorganic particle carrying | support honeycomb filter is demonstrated.
First, a honeycomb filter 100 before supporting inorganic particles is prepared. The honeycomb filter 100 can be obtained by a known method.

  Subsequently, a mixture for coating inorganic particles is prepared. The mixture for coating inorganic particles is a liquid containing a dispersion medium, thermoplastic resin particles, and inorganic particles.

  The dispersion medium disperses the thermoplastic resin particles and the inorganic particles. Examples of the dispersion medium are water and organic solvents such as ethanol and methanol.

  Examples of the thermoplastic resin constituting the thermoplastic resin particles are ethylene vinyl acetate copolymer; vinyl acetate resin; acrylic resin such as polymethyl methacrylate; and polyester resin such as polyethylene terephthalate.

  In order to improve the dispersibility in a dispersion medium such as water, a so-called thermoplastic resin emulsion can be used. A thermoplastic resin emulsion is obtained by polymerizing a monomer by emulsion polymerization in the presence of an emulsifier in a dispersant, and thermoplastic resin particles covered with the emulsifier are dispersed in a dispersion medium such as water. That is, a thermoplastic resin emulsion containing inorganic particles can be suitably used as a mixture for coating inorganic particles.

  From the viewpoint of suitably fluidizing the thermoplastic resin in the pores of the honeycomb filter, the average particle diameter D50 of the thermoplastic resin particles can be 0.1 to 10 μm. This average particle diameter D50 can be 0.5 μm or more, and can also be 5 μm or less. In this specification, the average particle diameter D50 is a median diameter in a volume-based particle size distribution obtained by measurement by a laser diffraction particle size distribution measurement method.

The inorganic particles are not particularly limited as long as they are inorganic particles that can function as a catalyst or a catalyst carrier. Examples of inorganic particles include alumina particles, silica particles, magnesia particles, titania particles, zirconia particles, ceria particles, La ₂ O ₃ particles, BaO particles, zeolite particles and other inorganic oxides, or one or more of these It is a complex oxide containing.

From the viewpoint of forming a layered inorganic particle layer in the pores, the average particle diameter D50 of the inorganic particles can be 0.1 to 10 μm. The average particle diameter D50 can be 1 μm or more, and can also be 3 μm or less.
The ratio between the average particle diameter of the thermoplastic resin particles and the average particle diameter of the inorganic particles, that is, (average particle diameter D50 of thermoplastic resin particles) / (average particle diameter D50 of inorganic particles) is 0.1-10. It is preferable that it is, and it is more preferable that it is 0.2-5.

  These inorganic particles may carry fine particles of at least one metal element selected from the group consisting of Pt, Pd, Rh, silver, vanadium, chromium, manganese, iron, cobalt, nickel, and copper. The mixture for coating inorganic particles may contain a precursor of these metal elements.

  In order to suitably disperse the thermoplastic resin particles and the inorganic particles in the dispersion medium, the mixture may contain a dispersion / emulsifier such as a known surfactant.

  Furthermore, the mixture for coating inorganic particles can contain additives such as a viscosity modifier.

  The amount of the thermoplastic resin particles in the mixture can be 3 to 30% by mass. The amount of inorganic particles in the mixture can be 15 to 30% by mass. The ratio of the mass of the thermoplastic resin particles to the mass of the inorganic particles can be 0.1 to 2.0. The solid content ratio in the mixture, that is, the ratio of the total mass of the thermoplastic resin particles and the inorganic particles can be 17 to 33% by mass.

(Impregnation process)
Subsequently, the honeycomb filter 100 is impregnated with the mixture for coating inorganic particles. As the impregnation method, a known method such as a dipping method or a coating method can be employed. As a result, the mixture is supplied to the surface of the flow path of the honeycomb filter 100 and the pores.

(Dispersion medium removal process)
Subsequently, the dispersion medium is removed from the inorganic particle coating mixture impregnated in the honeycomb filter 100 to obtain a particle-attached honeycomb filter. Examples of the method for removing the dispersion medium include natural drying, heat drying, ventilation drying, microwave drying, and vacuum drying. As a result, as shown in FIG. 3A, a porous material M1 containing inorganic particles and thermoplastic resin particles in the pores of the honeycomb filter and having many voids is formed. Here, (a) of FIG. 3 is a schematic diagram of the pores P, the inlet channel 110a, and the outlet channel 110b of the honeycomb structure 120. The porous material M1 is distributed so as to block most of the pores.

(Heating process)
Subsequently, the particle-attached honeycomb filter is heated. Thus, first, as shown in FIG. 3B, when the temperature exceeds the melting point of the thermoplastic resin, the thermoplastic resin particles in the porous material M1 melt and flow, and the surface of the honeycomb structure 120 It is considered that a thin thermoplastic resin layer M2 containing inorganic particles is formed along the line. Unlike the porous material M1 before flowing, the thermoplastic resin layer M2 has a dense structure rather than a porous structure, and the apparent volume is reduced. Therefore, there is a remaining space P2 in the pores P of the honeycomb structure 120. Secured.

  Subsequently, when the temperature rises further, thermal decomposition and / or combustion occurs, and the thermoplastic resin in the thermoplastic resin layer M2 disappears. Normally, if there is no oxygen in the atmosphere, only thermal decomposition occurs, and if there is oxygen in the atmosphere, thermal decomposition and combustion occur. If the resin is highly thermally decomposable, it can be thermally decomposed even in a non-oxygen atmosphere, but if it is performed in an oxygen atmosphere such as an air atmosphere, the resin can be easily removed.

  By this step, the resin portion is removed from the thermoplastic resin layer M2, and the inorganic particle layer M3 composed of inorganic particles is formed on the inner wall surfaces of the pores P of the honeycomb structure 120 and the inner surfaces of the flow paths 110a and 110b. Formed (see FIG. 2). At this time, the remaining space P2 is maintained without being closed.

  In the inorganic particle layer M3, a gap is formed between the inorganic particles by removing the resin.

  The maximum heating temperature can be set to 400 ° C. to 600 ° C., for example. Moreover, the temperature increase rate to the maximum heating temperature can be set to 100 ° C./hour to 500 ° C./hour. The maintenance time of the maximum heating temperature can be 30 minutes to 2 hours.

  According to the present embodiment, by impregnating a mixture containing inorganic particles and thermoplastic resin particles, the inorganic particles have the above-described structure by suitably moving the inorganic particles in accordance with the flow of the thermoplastic resin particles in the heating process. A supported honeycomb filter is obtained. In addition, when impregnating not the particulate inorganic substance but the aqueous solution in which the inorganic substance is dissolved and the solution containing the thermoplastic resin particles, the above structure tends not to be obtained because the inorganic substance does not move in the heating process.

  Further, when non-thermoplastic resin particles are used instead of thermoplastic resin particles, the resin does not flow. Furthermore, when a thermoplastic resin that dissolves in water instead of particles is used, it is difficult to sufficiently impregnate the coating liquid in the pores because the viscosity of the coating liquid increases.

Next, examples of the present invention will be described.
Example 1
A honeycomb filter 100 made of aluminum titanate was prepared. The outer diameter was 25.4 mm, the length was 50 mm, the cell density was 300 cpsi, and the honeycomb structure 120 had a porosity of 58%.

(1) Slurry (mixture for coating inorganic particles) A water slurry containing inorganic particles (zeolite particles) having an average particle diameter of 1.0 μm and a thermoplastic resin emulsion were prepared. Subsequently, these mixtures are prepared so that it becomes inorganic particle: thermoplastic resin particle: water | moisture content = 25: 13: 92 (mass ratio), and it spreads for 10 minutes with a propeller stirrer, The slurry of solid content 29 mass% is obtained. Obtained. As the thermoplastic resin emulsion, an emulsion of ethylene-vinyl acetate resin particles having an average particle size of 0.9 μm was used.

(2) Impregnation and drying step After the above honeycomb filter was submerged in the obtained slurry, the honeycomb filter was pulled up from the slurry, and excess slurry was sucked and removed from the honeycomb filter to dry the honeycomb filter. This process was repeated three times. FIG. 4 shows a cross-sectional SEM photograph of the honeycomb structure after impregnation and drying. The E portion is the honeycomb structure 120, the F portion (light gray) present in the pores of E is inorganic particles, and the G portion (dark gray) present in the pores of E is thermoplastic resin particles. , F and G form the porous material M1. The porous material M1 is formed so as to substantially block some of the pores.

(3) Heating process The honeycomb filter was heat-treated at 650 ° C. for 3 hours in an air atmosphere, whereby the resin flowed and pyrolyzed / burned to obtain a honeycomb filter having an inorganic particle layer. The temperature was increased to 650 ° C. at a speed of 300 ° C./h. FIG. 5 shows a cross-sectional SEM photograph of the honeycomb structure of the obtained inorganic particle-supporting honeycomb filter. The white portion is the honeycomb structure 120, the gray portion is the inorganic particle layer M3, and the black portion is the portion where the inorganic particle layer M3 in the pores P of the honeycomb structure does not exist. The amount of inorganic particles supported as a catalyst was 62 cm ³ / L per unit volume of the honeycomb structure.

(Example 2)
In the slurry adjustment step, inorganic particles: thermoplastic resin particles: water = 25: 38: 140 (weight ratio), a slurry having a solid content of 31% was adjusted, and the impregnation and drying steps were repeated twice. Except for this, the procedure was the same as in Example 1. The amount of inorganic particles supported on the obtained honeycomb filter was 43 cm ³ / L per unit volume of the honeycomb structure.

(Example 3)
Example 1 was repeated except that the impregnation and drying steps were repeated four times. The amount of inorganic particles supported on the obtained honeycomb filter was 70 cm ³ / L per unit volume of the honeycomb structure.

(Comparative Example 1)
In the slurry adjustment step, except that the thermoplastic resin particles were not added, and correspondingly the water content was reduced to 60 parts by mass to a solid content ratio of 29.4%, and the impregnation and drying steps were performed once. The same as in Example 1. FIG. 6 shows a cross-sectional SEM photograph of the honeycomb structure of the obtained inorganic particle-supporting honeycomb filter.

(Comparative Example 2)
Example except that, in the slurry preparation step, crosslinked polymethyl methacrylate particles (average particle size 0.9 μm) as non-thermoplastic resin particles were added instead of ethylene vinyl acetate resin as thermoplastic resin particles. Same as 1. FIG. 12 shows a cross-sectional SEM photograph of the honeycomb structure of the obtained inorganic particle-supporting honeycomb filter.

(Analysis of inorganic particle layer)
For the analysis of the inorganic particle layer M3 of the obtained honeycomb structure, a cross-sectional SEM image of the honeycomb structure as shown in FIG. 7 (for example, magnification 150, specifically, 1280 pixels with a width of about 850 μm and a width of 600 μm) 960 pixels) and image analysis software (ImageJ (free software)).

In the calculation of the area a [μm ² ] of the inorganic particle layer M3, a rectangular shape having substantially the entire thickness direction of the partition walls of the honeycomb structure in the longitudinal direction and having a lateral direction approximately twice as long as the thickness direction of the partition walls. The analysis region F was set (specifically, 265 × 530 μm), and the area of the gray portion in this analysis region was determined to determine the area a of the inorganic particle layer.

Next, in the analysis region F described above, a method for obtaining a portion of the contour line of the inorganic particle layer M3 that is not in contact with the honeycomb filter 100 will be described by taking the case of FIG. 7 as an example. From the cross-sectional SEM photograph of FIG. 7, an image in which only the portion of the honeycomb structure 120 (the white portion in FIG. 7) is extracted as black and the other portions are white is obtained. The expansion process is performed outward for one pixel (0.66 μm), and an image A (FIG. 8) of the honeycomb structure 120 is acquired. Next, an image obtained by extracting only the portion of the inorganic particle layer M3 (gray portion of FIG. 7) is obtained from the cross-sectional SEM photograph of FIG. An image B (FIG. 9) in which only white is expressed is acquired. Subsequently, the image A and the image B are overlapped with a transmittance of 50% to obtain an image C (FIG. 10). In the image C, a line represented by a white dot in a gray region is a portion not in contact with the honeycomb structure 120 in the outline of the inorganic particle layer M3 in FIG. Therefore, the above b [μm] can be obtained by measuring the length of the line represented by the white dot in the same analysis region F as described above in FIG.

  Subsequently, a / b was determined based on the obtained value. The results are shown in Table 1.

(Measurement of pressure loss due to accumulated soot)
The soot generation rate is 10 g / h, the gas flow rate is 6 m ³ / h, the gas temperature is gradually deposited on each filter, the change in pressure loss is measured, and the soot per apparent volume of the honeycomb filter is 4.5 g / h The pressure loss when L was deposited was determined. The results are shown in Table 1.

(Measurement of trap collection efficiency)
The soot collection efficiency was measured by supplying a gas containing soot from the inlet side of the filter, guiding the gas discharged from the outlet side to a particle counter, and measuring the number of leaking particles. The soot collection efficiency of soot is expressed by the following equation from the concentration of soot in the gas discharged from the filter outlet side at t = 360 s, where t = 0s is the timing when the gas containing soot starts to flow through the filter. Asked.

Trap collection efficiency (%) = 100 (1-N360s / N0)
N0: number concentration of soot in supplied gas (pieces / cm ³ )
N360s: number concentration of soot (gas / cm ³ ) in the gas discharged from the filter outlet at t = 360s
The results are shown in Table 1. Here, the case where the trapping efficiency of the soot was 80% or more was marked with ◯, and the case where it was less than 80% was marked with ×.

(Amount of inorganic particles supported)
The amount of inorganic particles supported per cubic volume of the honeycomb structure (cm ³ / L) is calculated from the weight difference before and after the inorganic particle supporting step, and the amount of inorganic particles (g) per 1 L of apparent volume of the honeycomb structure is calculated. Then, this value can be obtained by dividing by the true density (g / cm ³ ) of the inorganic particles. The results are shown in Table 1.

(Porosity of inorganic particle layer)
A photograph of about 5000 times the cross section of the inorganic particle layer was taken, and the porosity of the inorganic particle layer was determined by image processing. (A) and (b) of FIG. 11 show magnified photographs at a magnification of 5000 times of the inorganic particle layers of Example 1 and Comparative Example 1, respectively. White parts are inorganic particles.

In Examples 1 to 3, the soot storage pressure loss was less likely to increase than Comparative Examples 1 and 2, and soot collection efficiency was high. In Comparative Example 2, pores derived from the crosslinked PMMA particles were observed in the inorganic particle layer because the particles did not flow (FIG. 12).

  DESCRIPTION OF SYMBOLS 100 ... Honeycomb filter, 110a ... Inlet flow path, 110b ... Outlet flow path, 120 ... Honeycomb structure, 130 ... Sealing part, M1 ... Porous material, M2 ... Thermoplastic resin layer, M3 ... Inorganic particle layer, 200 ... Inorganic Particle-supporting honeycomb filter.

Claims (9)

A porous honeycomb structure having a plurality of flow paths;
One end of a part of the plurality of channels, and a plurality of sealing portions for closing the other end of the remaining channel among the plurality of channels;
An inorganic particle layer supported on the honeycomb structure,
In the cross section of the honeycomb structure, a [μm] is the total length of the portion of the contour line of the inorganic particle layer that is not in contact with the honeycomb structure.
In the cross section, when the total area of the inorganic particle layer is b [μm ² ],
An inorganic particle-supporting honeycomb filter having a / b of 0.15 to 0.3 [1 / μm].   The inorganic particle-supporting honeycomb filter according to claim 1, wherein the porosity of the inorganic particle layer is 47 to 65%.   The inorganic particle-supporting honeycomb filter according to claim 1 or 2, wherein a porosity of the honeycomb structure is 40 to 75%. The inorganic particle-carrying honeycomb filter according to any one of claims 1 to ³ , wherein a total volume of inorganic particles per apparent unit volume of the honeycomb structure is 30 to 110 cm3 / L. Impregnating a honeycomb filter with a mixture containing a dispersion medium, thermoplastic resin particles, and inorganic particles;
Removing the dispersion medium from the mixture impregnated in the honeycomb filter to obtain a particle-attached honeycomb filter;
Heating the particle-attached honeycomb filter, and removing the thermoplastic resin by thermal decomposition and / or combustion.   The method according to claim 5, wherein an average particle diameter D50 of the thermoplastic resin particles is 0.1 to 10 μm.   The method according to claim 5 or 6, wherein the resin of the thermoplastic resin particles includes an ethylene vinyl acetate resin.   The method according to any one of claims 5 to 7, wherein an average particle diameter D50 of the inorganic particles is 0.1 to 10 µm.   The method of any one of Claims 5-8 whose ratio of the average particle diameter of the said thermoplastic resin particle and the average particle diameter of the said inorganic particle is 0.1-10.