Patent Publication Number: US-2020298155-A1

Title: Method for producing honeycomb structure

Description:
FIELD OF THE INVENTION 
     The present invention relates to a method for producing a honeycomb structure. More particularly, it relates to a method for producing a honeycomb structure, which can improve a production efficiency of the honeycomb structure by suppressing application unevenness generated when applying a joining material to surfaces of honeycomb segments and preventing the joining material from dripping from a joining material discharging port of a nozzle portion of a joining material applicator. 
     BACKGROUND OF THE INVENTION 
     Conventionally, an internal combustion engine incorporates a diesel particulate filter (DPF) to collect fine particles contained in an exhaust gas from a diesel engine. Further, the internal combustion engine may incorporate a gasoline particulate filter (GPF) to collect fine particles contained in an exhaust gas from a gasoline engine. The DPF and GPF are formed by joining a plurality of porous honeycomb segments such as silicon carbide (SiC) through a joining material, and have a structure obtained by grinding an outer periphery of a segment joined body having the joined honeycomb segments to form a honeycomb structure having an appropriate shape such as a circle and an ellipse, and then coating the outer peripheral surface with a coating material. 
     Patent Document 1 discloses a method for producing a honeycomb structure by joining a plurality of porous honeycomb segments through a joining material to produce a segment joined body. In the method for producing the honeycomb structure as described in Patent Literature 1, as shown in  FIG. 1 , a plurality of porous honeycomb segments  10  are stacked along an L-shaped receiving plate  30  via adhesive layers  20  to obtain a desirable stacked structure, and then applying a pressure onto the entire structure. This leads to production of a segment joined body (honeycomb structure  40 ) in which the porous honeycomb segments  10  are vertically and horizontally stacked. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: Japanese Patent Application Publication No. 2004-262670 A 
     SUMMARY OF THE INVENTION 
     In the production of the joined body of the porous honeycomb segments  10  as shown in  FIG. 1 , the joining material is generally applied between adjacent porous honeycomb segments  10  from the nozzle portion of the joining material applicator to form the adhesive layers  20 . However, due to recent regulations, replacement of a refractory ceramic fiber (RCF)-free joining material changes properties of the conventional joining material, which cases a problem that the joining material cannot be uniformly applied. In particular, when a joining material having a higher thixotropic property is applied, responsiveness of the joining material is poor, for example, the joining material does not immediately respond to stress, so that application unevenness of the joining material will tend to occur. 
     Specifically, when the joining material is applied to the surfaces of the porous honeycomb segments through the nozzle portion of the joining material applicator, the application unevenness may occur at an application starting point and an application end point for the joining material as shown in  FIG. 1 . Further, the application unevenness may occur between the application starting point and the application end point due to pulsation of the joining material. 
     Further, as shown in  FIG. 3 , an application width of the joining material may be non-uniform. If an application amount is increased in order to solve the non-uniformity, it will cause a problem that when the honeycomb segments are joined as shown in  FIG. 4 , an excessive amount of the joining material protrudes to decrease an efficiency for using the joining material. 
     Further, when the joining material is applied through the nozzle portion of the joining material applicator, the joining material is not smoothly applied through the nozzle portion, and an increased amount of the joining material may be dripped from the joining material discharging port of the nozzle portion as shown in  FIG. 5 . An increased amount of the joining material dripped causes a problem of frequent cleaning of the nozzle portion. 
     All of the problems as described above cause deterioration of production efficiency of the honeycomb structure. In view of such circumstances, an object of the present invention is to suppresses application unevenness when applying the joining material onto the surfaces of the honeycomb segments and prevent the joining material from dripping from the joining material discharge port of the nozzle portion of the joining material applicator, thereby improving the production efficiency of the honeycomb structure. 
     As a result of intensive studies, the present inventors have presumed that the application unevenness when applying the joining material and the dripping of the joining material from the joining material discharge port of the nozzle portion of the joining material applicator are caused by a pressure of the joining material, generated inside the nozzle portion of the joining material applicator. Then, the present inventors have found that these problems can be solved by having a certain structure of the nozzle portion of the joining material applicator. Thus, the present invention is specified as follows: 
     A method for producing a honeycomb structure for fine particle collection filters, the honeycomb structure comprising a plurality of porous honeycomb structure segments joined together via joining material layers, each of the porous honeycomb structure segment comprising: partition walls made of a SiC material, the partition walls defining a plurality of cells to form flow paths for a fluid, each of the cells extending from an inflow end face that is an end face on a fluid inflow side to a fluid outflow end face that is an end face on a fluid inflow side; and an outer peripheral wall located at the outermost periphery, the method comprising: 
     joining each of the porous honeycomb segments via the joining material layers by applying a joining material between joining surfaces of each of the porous honeycomb structure segments, through a nozzle portion of a joining material applicator, 
     wherein the nozzle portion of the joining material applicator comprises: 
     a joining material introduction port; 
     a joining material discharge space having a slit-shaped joining material discharge port for discharging an introduced joining material; and 
     a joining material flow path having a bent portion, through which the joining material passes from the joining material introduction port to the joining material discharge space; and 
     wherein the joining material flow path of the nozzle portion comprises a buffer space configured such that a flow path cross section gradually expands toward the joining material discharge space on a downstream side of the bent portion. 
     According to the present invention, it is possible to suppresses application unevenness when applying the joining material onto the surfaces of the honeycomb segments and prevent the joining material from dripping from the joining material discharge port of the nozzle portion of the joining material applicator, thereby improving the production efficiency of the honeycomb structure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view showing a conventional honeycomb segment and a manner of producing a segment joined body by joining the honeycomb segments. 
         FIG. 2  is an appearance observation photograph showing application unevenness and pulsation of a joining material in the conventional honeycomb segment. 
         FIG. 3  is an appearance observation photograph showing a variation in an application width of a joining material in the conventional honeycomb segment. 
         FIG. 4  is an appearance observation photograph showing extrusions of a joining material in the conventional segment joined body. 
         FIG. 5  is an appearance observation photograph showing dripping of a joining material from a joining material discharge port of a nozzle portion of a conventional joining material applicator. 
         FIG. 6  is a schematic external view of a honeycomb structure according to an embodiment of the present invention. 
         FIG. 7  is a schematic external view of a porous honeycomb segment according to an embodiment of the present invention. 
         FIG. 8  is an appearance observation photograph of a nozzle portion  60  of a joining material applicator according to an embodiment of the present invention. 
         FIG. 9  is an appearance observation photograph schematically showing an internal structure of the nozzle portion  60  of the joining material applicator according to an embodiment of the present invention. 
         FIG. 10  is an appearance observation photograph of a flat-shaped spacer that partitions a joining material discharge space of a nozzle portion main body according to an embodiment of the present invention. 
         FIGS. 11A,11B and 11C  are each an appearance observation photograph of a flat-shaped spacer that partitions a buffer space according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, embodiments of a honeycomb structure according to the present invention will be specifically described with reference to the drawings. It is to understand that the present invention is not limited to the following embodiments, and various design modifications and improvements may be made based on ordinary knowledge of a person skilled in the art, without departing from the scope of the present invention. 
     (Method for Producing Honeycomb Structure) 
       FIG. 6  is a schematic external view of a honeycomb structure  100  produced by a method for producing a honeycomb structure according to an embodiment of the present invention. The honeycomb structure  100  is formed by binding a plurality of porous honeycomb structure segments  50  together via joining material layers  54 , in which each porous honeycomb structure segment  50  includes: partition walls  52  made of a SiC material, which define a plurality of cells  51  to form flow paths for a fluid, and which extend from an inflow end face that is an end face on a fluid inflow side to an outflow end face that is an end face on a fluid outflow side; and an outer peripheral wall  53  located at the outermost periphery. Here, the SiC material means a material mainly based on SiC (silicon carbide), including, for example, a material consisting only of SiC such as recrystallized SiC, Si—SiC based composite materials, cordierite-SiC based composite materials, metal silicon-impregnated SiC, and the like. 
     The honeycomb structure  100  is formed by grinding the outer periphery into an appropriate shape such as a circular shape and an elliptical shape, and then coating the outer peripheral surface with a coating material, and is used as a fine particle collection filter such as a diesel engine particulate filter (DPF) and a gasoline particulate filter (GPF). The inflow end face or the outflow end face of the cells  51  serving as the flow paths for the fluid in the honeycomb structure  100  are provided with plugged portions, whereby fine particles (such as carbon fine particles) in an exhaust gas can be collected. Although the plugged portions may be provided at any time, but it is more preferable to provide the plugged portions before firing the porous honeycomb segments  50 , because the plugged portions and the partition walls  52  are sintered by the firing. 
     For the honeycomb structure  100 , a catalyst may be further provided on surfaces or inner side of the partition walls  52  made of a SiC material that define the plurality of cells  51 . A type of the catalyst is not particularly limited, and it can be appropriately selected according to the use purpose and application of the honeycomb structure  100 . Examples of the catalyst include noble metal catalysts or catalysts other than them. Illustrative examples of the noble metal catalysts include a three-way catalyst and an oxidation catalyst obtained by supporting a noble metal such as platinum (Pt), palladium (Pd) and rhodium (Rh) on surfaces of pores of alumina and containing a co-catalyst such as ceria and zirconia, or a lean nitrogen oxides trap catalyst (LNT catalyst) containing an alkaline earth metal and platinum as storage components for nitrogen oxides (NO x ). Illustrative examples of a catalyst that does not use the noble metal include a NOx selective catalytic reduction catalyst (SCR catalyst) containing a copper-substituted or iron-substituted zeolite, and the like. Further, two or more catalysts selected from the group consisting of those catalysts may be used. A method for supporting the catalyst is not particularly limited, and it can be carried out according to a conventional method for supporting the catalyst on the honeycomb structure  100 . 
     In the method for producing the honeycomb structure according to an embodiment of the present invention, first, porous honeycomb segments  50  as illustrated in  FIG. 7  are produced. As the production step of the porous honeycomb segments  50 , first, a binder, a dispersant (surfactant), a pore former, water, and the like are added to a ceramic raw material made of a SiC material, and these are mixed and kneaded to prepare a green body. The prepared green body is then formed into a honeycomb shape by an extrusion molding method to obtain a raw (unfired) pillar shaped honeycomb formed body. The pillar shaped honeycomb formed body extruded from an extruder is cut into an appropriate length. The extrusion molding method can be carried out using an apparatus such as a ram type extruder, a bi-axial screw type continuous extruder or the like. For forming the honeycomb shape, a method using a die having a desired cell shape, partition wall thickness, and cell density is preferable. Thus, an unfired honeycomb formed body is produced. 
     An outer shape of the unfired pillar shaped honeycomb structure is not particularly limited, and it may be a pillar shape with rectangular end faces as in the present embodiment, or a pillar shape with circular end faces (circular pillar shape), or a pillar shape with polygonal (triangular, pentagonal, hexagonal, heptagonal, octagonal, etc.) end faces, except for rectangular end faces. 
     The unfired honeycomb formed body is then dried to produce a honeycomb dried body. The drying may be carried out by dielectric drying using high-frequency energy generated by passing a current through the porous honeycomb segments  50 , or may be carried out by hot air drying which introduces hot air into the porous honeycomb segments  50 . Further, natural drying left at room temperature, microwave drying using a microwave, freeze drying, or the like may be carried out, or a combination of a plurality of drying methods may be carried out. Subsequently, the honeycomb dried body is fired. In this case, the plugged portions are provided by sintering a plugging material on both end faces of the honeycomb dried body so as to form segments, in order to purify fine particles (carbon fine particles and the like) in an exhaust gas. The plugged portions are formed in each cell on both end faces. When a cell is plugged on one end face, its opposite end face is not plugged. Such plugging can provide a filter function. Thus, the porous honeycomb segments  50  are produced. 
     The joining material is applied to each of the plurality of porous honeycomb segments  50  between the joining surfaces using the joining material applicator to join them via the joining material layers  54 . In the joining step, a plurality of porous honeycomb segments  50  may be stacked along an L-shaped receiving plate via the joining material layers  54  using the method shown in  FIG. 1  to form a desired stacked structure, and then applying a pressure to the entire structure to join them. Thus, the honeycomb structure  100  as shown in  FIG. 6  is produced. 
     The joining material forming the joining material layers  54  is not particularly limited as long as it can join the surfaces of the outer peripheral walls  53  made of the SiC material to each other with good adhesive strength. The joining material forming the joining material layers  54  may contain, for example, inorganic particles, and inorganic fibers and colloidal oxides as other components. Further, during the joining of the porous honeycomb segments  50 , in addition to those components, an organic binder such as methylcellulose and carboxymethylcellulose, a dispersant, water and the like may be optionally added, and mixed and kneaded using a kneader such as a mixer to form a paste, which may be used as a joining material. 
     Examples of materials for forming the inorganic particles contained in the joining material forming the joining material layers  54  includes ceramics selected from the group consisting of silicon carbide, silicon nitride, cordierite, alumina, mullite, zirconia, zirconium phosphate, aluminum titanate, titania, and combinations thereof; Fe—Cr—Al-based metals; nickel-based metals; silicon-silicon carbide-based composite materials; and the like. 
     Examples of the inorganic fibers contained in the joining material forming the joining material layers  54  include ceramic fibers such as aluminosilicate and silicon carbide, and metal fibers such as copper and iron. Suitable colloidal oxides include silica sol, alumina sol and the like. The colloidal oxides are suitable for providing a suitable adhesive force to the joining material, and can also be bonded to the inorganic fibers and the inorganic particles by drying and degreasing them to provide a strong joining material having improved heat resistance after drying. 
     In the method for producing the honeycomb structure according to an embodiment of the present invention, when the joining material is applied to each of the plurality of porous honeycomb segments  50  between the joining surfaces, a nozzle portion of the joining material applicator, which has the following structure, is used. This can suppress application unevenness during application of the joining material to the surfaces of the honeycomb segments and prevent the joining material from dripping from a joining material discharge port of the nozzle portion of the joining material applicator. As a result, a production efficiency of the honeycomb structure can be improved. 
     (Structure of Nozzle Portion of Joining Material Applicator) 
       FIG. 8  is an appearance observation photograph of a nozzle portion  60  of the joining material applicator according to an embodiment of the present invention.  FIG. 9  is an appearance observation photograph schematically showing an internal structure of the nozzle portion  60  of the joining material applicator according to an embodiment of the present invention. 
     The nozzle portion  60  of the joining material applicator includes a nozzle portion main body  66  and a spacer  67 . The nozzle portion main body  66  includes: joining material introduction port  61  into which the joining material prepared in the joining material applicator is introduced; a joining material discharge space  63  having a slit-shaped joining material discharge port  64  for discharging the introduced joining material; and a joining material flow path  62  having a bent portion  65 , through which the joining material passes from the joining material introduction port  61  to the joining material discharge space  63 . The spacer  67  is inserted into the joining material discharge space  63  of the nozzle portion main body  66 . 
     The nozzle portion main body  66  may be formed of any material known for a joining material applying nozzle. The nozzle portion main body  66  can be formed of, for example, aluminum, iron, copper, or an alloy such as SUS, or a resin such as polyethylene, vinyl chloride, fluororesin and polycarbonate. 
     A cross section of the flow path for the joining material in the joining material introduction port  61  and the joining material flow path  62  may have any shape, including, for example, a circular shape, an elliptical shape, or a polygonal shape. A size of the cross section of the flow path for the joining material can be appropriately designed according to the size of the nozzle portion  60  and the like, and for example, the cross section can be formed in a circular shape having a diameter of from 5.0 to 20.0 mm. 
     The joining material flow path  62  has the bent portion  65 .  FIG. 9  illustrates a structure in which the joining material flow path  62  connected to the joining material introduction port  61  straightly extends as it is, bends at approximately 90° at the bent portion  65 , and extends to the joining material discharge space  63  on the downstream side of the bent portion  65 . The joining material flow path  62  is not limited to that is bent at approximately 90° at the bent portion  65  as described above, and it may be bent at any angle. The joining material introduced from the joining material introduction port  61  into the joining material flow path  62  is thinly stretched in the joining material discharge space  63  by passing through the bent portion  65 , and is discharged through the joining material discharge port  64 . The bent portion  65  can prevent a difference in flow velocity between both ends and the center of the slit-shaped joining material discharge port  64  when the joining material is thinly stretched by the joining material discharge space  63 . 
     A size of the slit-shaped joining material discharge port  64  of the joining material discharge space  63  can be appropriately designed according to the size of the nozzle portion  60 , an application width and an application amount of the joining material. For example, the slit-shaped joining material discharge port  64  can be formed into a rectangular shape having a length of 60 mm and a width of from 25 to 45 mm. The joining material discharge space  63  can be formed by inserting a flat-shaped spacer as shown in  FIG. 10  into the joining material discharge space  63  of the nozzle portion main body  66  to partition it. In the joining material discharge space  63  partitioned by the flat-shaped spacer shown in  FIG. 10 , a space width  70  is increased toward the joining material discharge port  64 . Accordingly, the joining material discharge space  63  can be formed so as to expand the flow path cross section of the joining material from introduction of the joining material from the joining material flow path  62  to discharge through the joining material discharge port  64 . This structure can prevent a difference in flow velocity between both ends and the center of the slit-shaped joining material discharge port  64 . 
     The joining material flow path  62  includes a buffer space  68  which is adjacent to the joining material discharge space  63  on the downstream side of the bent portion  65  and which is configured such that the flow path cross section gradually expands toward the joining material discharge space  63 . The joining material that has passed through the joining material flow path  62  is introduced into the joining material discharge space  63  as described above, and then discharged through the slit-shaped joining material discharge port  64  of the joining material discharge space  63 . In this case, a constant size of the flow path cross section of the joining material flow path  6  increases a pressure inside the nozzle portion  60 , for example when the joining material has high thixotropy and poor response. In contrast, according to the embodiment of the present invention, the buffer space  68  of the joining material flow path  62  is provided, thereby expanding the flow path cross section of the joining material prior to introduction into the joining material discharge space  63 , so that an increase in a pressure inside the nozzle portion  60  can be suppressed. Therefore, the application unevenness can be satisfactorily suppressed for example when applying the joining material to the surfaces of the porous honeycomb segments through the nozzle portion  60  of the joining material applicator. Further, since the joining material can be smoothly discharged through the slit-shaped joining material discharge port  64  of the joining material discharge space  63 , the application width of the joining material becomes uniform, so that the dripping of the joining material from the joining material discharge port  64  of the nozzle portion  60  can also be satisfactorily suppressed. 
     The buffer space  68  can be formed by partitioning with the flat-shaped spacer. The flat-shaped spacer may be an integral spacer formed so that the cross section of the flow path gradually expands. 
     The nozzle portion  60  of the joining material applicator according to an embodiment of the present invention further includes, as the buffer space, a buffer space  69  configured to extend from the buffer space  68  into the joining material discharge space  63 , in addition to the buffer space  68 . The buffer spaces  68  and  69  can be formed such that a plurality of flat-shaped spacers as shown in  FIGS. 11A, 11B and 11C  are stacked in order from the joining material flow path  62  side, and finally inserting the flat-shaped spacer as shown in  FIG. 10 . In the spacers of  FIGS. 11A, 11B and 11C , an area of an opening  71  corresponding to the flow path cross section gradually increases in that order. Therefore, the spacer of  FIG. 11A  which is adjacent to the joining material discharge space  63  and has the smallest area of the opening  71  is provided, the spacer of  FIG. 11B  is then provided and the spacer of  FIG. 11C  having the largest area of the opening  71  is further provided in the joining material discharge spaced, thereby forming a buffer structure in which the flow path of the joining material is gradually expanded. According to such a structure, the flow path of the joining material can be expanded until it is narrowed by the joining material discharge port  64 , so that retention of the joining material in the nozzle portion  60  can be satisfactorily suppressed. Further, by such a structure, the buffer space  69  of the joining material discharge space  63  can be expanded by 200 to 550%. 
     Thicknesses of the flat-shaped spacers as shown in  FIGS. 11A, 11B and 11C  are not particularly limited, and they may be, for example, from 1.0 to 10 mm, respectively. Further, the thicknesses of the plurality of spacers may be the same or different. 
     At least one of the plurality of flat-shaped spacers may also serve as a strainer by having a structure including partition walls  72  that partition the opening  71  in the form of parallel slits as shown in  FIG. 11B . Such a structure can allow foreign substances contained in the joining material to be collected, so that clogging of the nozzle portion  60  can be suppressed. 
     The material of the spacer that partitions the buffer space  68  is not particularly limited. For example, the spacer can be formed of aluminum, iron, copper, or an alloy such as SUS, or a resin such as polyethylene, vinyl chloride, fluororesin, or polycarbonate. 
     EXAMPLES 
     Hereinafter, examples will be provided for better understanding of the present invention and its advantages, but the present invention is not limited to these examples. 
     Test Example 1 
     As Test Example 1, porous honeycomb segments made of a SiC material were prepared. The length of each porous honeycomb segment in the cell extending direction was 141 mm. 
     Separately, a joining material applicator having a nozzle portion made of a SUS material and a fluororesin plate having the structure as shown in  FIGS. 8 and 9  was prepared. The buffer space of the joining material flow path of the nozzle portion was formed by stacking and partitioning the flat-shaped spacers shown in  FIGS. 11A, 11B and 11C . That is, in the joining material discharge space  63 , from the joining material flow path side, the spacer of  FIG. 11A  having the smallest area of the opening  71 , the spacer of  FIG. 11  B, and the spacer of  FIG. 11C  having the largest area of the opening  71  were arranged in this order, and the flat-shaped spacer as shown in  FIG. 10  was finally inserted. The thicknesses of the flat-shaped spacers shown in  FIGS. 11  A,  11  B and  11 C were 5 mm, 0.5 mm and 3 mm, respectively. The spacers of  FIGS. 11  A and  11 C were made of fluororesin, and the spacer of  FIG. 11B  was made of SUS304. The thickness of the flat-shaped spacer shown in  FIG. 10  was 1 mm, and the material was fluororesin. 
     The joining material contained inorganic fibers, and used a slurry mainly based on silicon carbide as ceramic powder, water as a dispersion medium, and colloidal silica as a binder. A shear stress value indicating viscosity of the joining material was 240 Pa. 
     The joining material was applied at a constant rate (100 mm/s) from one end of the joining surface to the other end of each porous honeycomb segment along the extending direction of the cells of the porous honeycomb segment through the nozzle portion. The application width was 37.0 cm. 
     After the application, the applied surfaces of the joining material in the porous honeycomb segments were observed, indicating that no application unevenness was found. Further, the dripping of the joining material from the joining material discharge port of the nozzle portion of the joining material applicator was also satisfactorily suppressed. 
     DESCRIPTION OF REFERENCE NUMERALS 
     
         
           10 , 50  porous honeycomb segment 
           20  adhesive layer 
           30  receiving plate 
           40 ,  100  honeycomb structure 
           51  cell 
           52  partition wall 
           53  outer peripheral wall 
           54  joining material layer 
           60  nozzle portion 
           61  joining material introduction port 
           62  joining material flow path 
           63  joining material discharge space 
           64  joining material discharge port 
           65  bend portion 
           66  nozzle portion main body 
           67  spacer 
           68 ,  69  buffer space 
           70  space width 
           71  opening 
           72  partition wall