JP4811662B2 - Manufacturing method of ceramic honeycomb filter - Google Patents

Description

  The present invention relates to a method for manufacturing a ceramic honeycomb filter in which predetermined cells of a ceramic honeycomb structure having a large number of cells partitioned by cell walls are plugged with a plugging material.

  Exhaust gas from diesel engines, etc. contains a large amount of particulate matter (particulate matter, hereinafter referred to as “PM”) mainly composed of black smoke, and when released into the atmosphere, the human body and environment Adversely affects. For this reason, an exhaust gas system such as a diesel engine is equipped with a filter for capturing and purifying PM. FIG. 2 shows an example of a ceramic honeycomb filter (hereinafter referred to as “honeycomb filter”) 20 that collects and purifies PM in automobile exhaust gas, (a) is a front view, and (b) is a partial cross section. It is a side view. In FIG. 2, a ceramic honeycomb structure (hereinafter referred to as “honeycomb structure”) 21 has a large number of cells 25a and 25b partitioned by cell walls 24 inside an outer peripheral wall 21a. Then, predetermined cells 25 a and 25 b on both end faces 22 a and 22 b of the honeycomb structure 21 are alternately plugged with plugging materials 23 a and 23 b to form the honeycomb filter 20. Although not shown, the honeycomb filter 20 is gripped so that the outer periphery of the outer peripheral wall 21a of the honeycomb structure 21 is not moved during use by a gripping member formed of a metal mesh or a ceramic mat or the like. Arranged in the storage container.

  In the honeycomb filter 20 as shown in FIG. 2, the exhaust gas is purified as follows. Exhaust gas (indicated by a dotted arrow) flows from the cell 25b that opens to the end face 22a. The PM contained in the exhaust gas is collected when passing through the cell wall 24, and the purified exhaust gas flows out of the cell 25a opened in the end face 22b and is released into the atmosphere.

  The honeycomb filter 20 as shown in FIG. 2 has been manufactured by the following process. First, ceramic powder and binder and other raw materials are weighed, mixed and kneaded to form a clay. Next, the clay is extruded from, for example, a honeycomb-shaped die of a screw type extruder. At the same time, it is cut into a predetermined length to obtain a formed body having a honeycomb structure. Next, the formed body is dried and fired to obtain the honeycomb structure 21. Further, in the plugging step, predetermined cells 25a and 25b on both end faces 22a and 22b of the honeycomb structure 21 are plugged with plugging materials 23a and 23b, respectively. 3A to 3C are schematic views of this plugging process. In FIG. 3A, after the masking film 31 is adhered to one end face 22a of the honeycomb structure 21, the masking film 31 is irradiated with laser light emitted from a laser oscillation unit (none of which is shown) of the laser processing apparatus. A position corresponding to the predetermined cell 25a is drilled. Next, in FIG. 3B, the plugging material 23 is filled into the cells 25 a from the holes 32 that are formed by immersing the bonding surface side of the masking film 31 of the honeycomb structure in the plugging material 23. Next, in FIG. 3C, the plugged material 23 after filling is cured and dried, and the honeycomb structure 21 in which the cells on one end face 22a side are alternately plugged with the plugged material 23a is obtained. . Similarly, the cells on the other end face 22b side are plugged alternately with the plugging material 23b, and the masking film 31 is further removed to obtain the honeycomb filter 20 shown in FIG.

  Regarding perforating the masking film with laser light, Patent Document 1 discloses that the cell position is recognized by image processing, and the masking film is perforated by laser light. The shape of the perforated hole is circular and the diameter thereof is the cell. It has been proposed to make the area 30 to 70%, preferably about 50%. According to Patent Document 1, even if there is a slight variation in cell pitch, the diameter of the hole drilled in the cell is small, so there is no fear of drilling across the cell wall or adjacent cells.

  The present applicant also disclosed in Patent Document 2 that the end face of the honeycomb structure is divided into a plurality of processing areas, and the masking film is perforated with laser light, and the dimensions of the perforated holes are made to follow the cell shape. It is proposed that the cell area be 40 to 90%. According to Patent Document 2 proposed by the present applicant, a cell that needs plugging can be reliably selected, and the masking film can be perforated without the laser beam hitting the cell wall. Since the hole from which the hole is removed has a sufficient size, the plugging material can penetrate the entire opening hole.

Japanese Patent Laid-Open No. 2001-300922 JP 2003-200010 A Japanese Utility Model Publication No. 4-43486

  In recent years, a honeycomb filter for a diesel engine has a large outer diameter of 300 mm, and the number of cells has become as large as tens of thousands, and the size of each cell has been reduced. In such a honeycomb filter, when perforating a masking film with a laser beam, it becomes difficult to fill the plugging material from the perforated hole, and the plugging material is not sufficiently fixed to the cell wall. As the plugging material is removed during use, the PM collection rate may be reduced. Therefore, it is necessary to increase the area ratio of the perforated hole to the cell opening area so that the plugging material is easily filled. However, as described in Patent Documents 1 and 2, when the area ratio of the perforated hole to the cell opening area is increased, the position of the perforated hole is shifted from the position to be perforated, and the cell Sometimes it was too close to the wall or straddled adjacent cells. As shown in FIG. 5 (a), when the position of the hole punched in the masking film extends from the cell 25a to be punched to the adjacent cell 25b that should not be punched, as shown in FIG. 5 (b). When the sealing material (slurry) 23 is filled, the plugging material 23 enters the adjacent cell 25b 34, and the amount of plugging material slurry filled in the cell 25a where the plugging material is to be provided is small. 2 and the strength of the plugging material cannot be obtained, or a part or the whole of the adjacent cell 25b that should not be provided with the plugging material 23a is blocked with the plugging material. A honeycomb filter in which the predetermined cells shown are alternately plugged at both end faces cannot be obtained, which may lead to a problem that the pressure loss of the honeycomb filter increases. Such a phenomenon is likely to occur when the area ratio of the perforated hole to the cell opening area exceeds 45%.

As a result of earnest study on the problem that the position of the drilled hole deviates from the cell to be drilled, the present inventor has made the galvanometer in the laser head change the traveling direction of the laser light emitted from the laser oscillation unit. It has been found that the temperature of this is generated because it fluctuates due to the laser beam. In particular, when the operation is started from a state in which the laser processing apparatus is stopped, the temperature of the galvanometer in the laser head rises due to the laser light, which causes a problem that the deviation of the laser light due to temperature drift becomes larger. It was.
With respect to the temperature drift problem of the galvanometer of this laser processing apparatus, in Patent Document 3, there is no description used to make a hole in the masking film, but when the temperature of the galvanometer is measured and the temperature exceeds a certain fluctuation range An image that gives a correction to the position data of the galvano control unit by detecting the deviation from the processing target by performing the image recognition of the processing point in response to the trigger signal generated from the temperature trigger unit A laser processing apparatus with a galvano temperature drift self-correction function having a processing unit has been proposed, and laser beam displacement due to temperature drift is eliminated in real time, and laser processing can be performed at an accurate position. However, such a laser processing apparatus with a galvano temperature drift self-correction function requires an image processing unit that detects a deviation from the processing target and corrects the position data of the galvano control unit. Mechanism was necessary.

  The present invention has been made in order to solve the above-mentioned problem that the position of the perforated hole deviates from the cell to be perforated, and it is difficult for the laser beam to shift due to temperature drift in the laser processing apparatus, and the masking film is accurately positioned. It is an object of the present invention to provide a method for manufacturing a ceramic honeycomb filter, which can perforate and does not require a complicated mechanism.

  In the case where 45% or more of the cell area is perforated with a laser beam at a position corresponding to a predetermined cell of the masking film adhered to the end face of the ceramic honeycomb structure, the inventors of the present invention have a laser beam caused by temperature drift. The following findings were obtained as a result of intensive investigations on a method that hardly causes a shift, can accurately perforate a predetermined position of the masking film, and can satisfactorily fill the plugging material. That is, as the temperature of the galvanometer in the laser head rises due to the laser beam, the laser beam is shifted due to the temperature drift, so that the temperature of the laser processing apparatus (particularly, the galvanometer in the laser head) is kept within a predetermined range. As a result, the inventors have obtained knowledge that the above problems can be solved, and have arrived at the present invention.

That is, in the present invention, a masking film is attached to an end face of a ceramic honeycomb structure having a large number of cells partitioned by cell walls, and then a predetermined amount of the masking film is applied by laser light emitted from a laser head of a laser processing apparatus. A position corresponding to the cell is perforated, and then, the bonding surface of the masking film is dipped in a plugging material, and the plugging material is filled into the predetermined cell from the perforated hole and plugged. A method for manufacturing a ceramic honeycomb filter, wherein when the laser beam punctures 45% or more of a cell area at a predetermined position of the masking film, a temperature of a galvanometer in the laser head is set to 36 ± 5 ° C. The masking film adhered to the honeycomb structure is perforated with the laser beam.
In the present invention, it is preferable that the laser beam is perforated with the laser beam at an ambient temperature of 23 ° C. ± 5 ° C.
Further, in the present invention, the laser beam is irradiated in the air, and the temperature of the galvanometer in the laser head is set to 36 ± 5 ° C., and the masking film attached to the ceramic honeycomb structure is punched with the laser beam. Is preferred.
Further, in the present invention, the laser beam is irradiated to the dummy body, the temperature of the galvanometer in the laser head is set to 36 ± 5 ° C., and the masking film attached to the ceramic honeycomb structure is perforated with the laser beam. It is preferable to do.

Next, the function and effect of the present invention will be described.
In the present invention, after a masking film is attached to an end face of a ceramic honeycomb structure having a large number of cells partitioned by cell walls, predetermined cells of the masking film are formed by laser light emitted from a laser head of a laser processing apparatus. And then plugging the surface of the masking film in a plugging material, filling the predetermined cells with the plugging material through the holes, and plugging the plugging material. A method for manufacturing a honeycomb filter, wherein when the laser beam punctures 45% or more of a cell area at a predetermined position of the masking film, the temperature of a galvanometer in the laser head is set to 36 ± 5 ° C. By punching the masking film attached to the structure with the laser beam, the following effects are obtained. A. That is, when the temperature of the galvanometer in the laser head fluctuates due to the laser light emitted from the laser oscillation unit, the deviation of the laser light increases due to the temperature drift, and the masking film is placed at an accurate position as shown in FIG. Cannot drill. However, when perforating 45% or more of the cell area, the temperature of the galvanometer in the laser head is set to 36 ° C. ± 5 ° C., so that the plugging material can be satisfactorily filled, and the temperature of the galvanometer is Since the laser beam is stable and hardly displaced, the masking film is punched at an accurate position so that the distance (d) from the cell wall 24 is within a predetermined range as shown in FIG. be able to. And, as shown in FIG. 5 (b), the position of the drilled hole is too close to the cell wall or straddles adjacent cells as shown in FIG. 5 (a). The material 23 permeates into the adjacent cell 25b (34), and the adjacent cell 25b that should not be provided with the plugging material suppresses occurrence of a defect that becomes a honeycomb filter partially or entirely blocked. be able to. Here, if the temperature of the galvanometer in the laser head is less than 31 ° C. or exceeds 41 ° C., the temperature drift of the laser beam is likely to occur, and the masking film cannot be stably punched at an accurate position.
In order to stably maintain the temperature of the galvanometer in the laser head as 36 ° C. ± 5 ° C., a heater may be installed in the vicinity of the galvanometer of the laser head.

In the present invention, it is preferable that the laser beam is perforated with the laser beam at an ambient temperature of 23 ° C. ± 5 ° C. for the following reason. By setting the ambient temperature of the laser processing device to 23 ° C. ± 5 ° C., the temperature difference between the temperature of the galvanometer in the laser head and the ambient temperature of the laser processing device is reduced, so that the temperature of the galvanometer in the laser head is further stabilized. This is because it is easy to perform, and it is possible to perforate with high positional accuracy in the masking film adhered to the honeycomb structure. In order to set the ambient temperature of the laser processing apparatus to 23 ° C. ± 5 ° C., for example, the laser processing apparatus can be installed in a temperature-controlled room set to 23 ° C. When the ambient temperature of the laser processing device is less than 20 ° C, the temperature difference between the temperature of the galvanometer in the laser head and the ambient temperature of the laser processing device becomes large, and the temperature of the galvanometer in the laser head is difficult to stabilize, so that the accurate position The masking film cannot be perforated. On the other hand, when the ambient temperature of the laser processing apparatus exceeds 26 ° C., the masking film is easily peeled off from the end face of the honeycomb structure, and it is not preferable because the handling of the honeycomb structure requires attention.
In the present invention, as shown in FIG. 4 (a), the plugging material is filled by perforating the masking film at a position where the distance (d) from the cell wall 24 is 0.01 to 0.2 mm. In this case, the plugging material can penetrate the entire cell opening hole, which is preferable.

In the present invention, it is preferable that the laser beam is irradiated and the temperature of the galvanometer in the laser head is set to 36 ± 5 ° C., and the masking film attached to the ceramic honeycomb structure is punched with the laser light. The reason is as follows. When operating from a state where the laser processing device is stopped, the galvanometer temperature in the laser head is greatly increased by the laser light emitted from the laser oscillator, and in the state where the galvanometer temperature is rising, the laser beam shifts due to temperature drift. Becomes larger. Further, since the output of the laser beam is not stable, the deviation of the laser beam becomes large. Therefore, until the temperature of the galvanometer in the laser head reaches 36 ± 5 ° C., the temperature of the galvanometer in the laser head is increased by irradiating the laser beam, and the output of the laser beam is stabilized, whereby FIG. As shown in a), the masking film can be punched at an accurate position so that the distance (d) from the cell wall 24 falls within a predetermined range.
In the present invention, the dummy body may be irradiated with the laser beam when the laser beam is irradiated in the sky. Any dummy body may be used as long as it can be irradiated with laser light. However, it is preferable to use a non-defective or defective ceramic honeycomb structure to which a masking film is attached. When a good or defective ceramic honeycomb structure with a masking film attached is used as a dummy body, the ceramic honeycomb structure actually used after the temperature of the galvanometer in the laser head laser head becomes 36 ° C. ± 5 ° C. Even if the body is set, it is preferable because the setting of the laser beam (for example, output, moving method, etc.) is not particularly changed, and the production can be promptly moved to production.

  According to the method for manufacturing a honeycomb filter of the present invention, the laser beam is not easily displaced due to temperature drift, the masking film can be perforated at an accurate position, and a complicated mechanism is not required. A method for manufacturing a honeycomb filter can be provided.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
(Embodiment 1 )
FIG. 1 is a schematic diagram of a laser processing apparatus 11 according to the present invention. In FIG. 1, a honeycomb structure 21 having masking films 31 attached to both end faces is set on an XY stage 12. Above the XY stage 12, a CCD camera 13 that images the end face of the honeycomb structure 21; A laser head 15 is provided, and a galvanometer for controlling the laser light emitted from the laser oscillation unit is accommodated in the laser head 15. In addition, a heater 17 is provided around the laser head 15 in order to stably maintain the temperature of the galvanometer 18 in the laser head at 36 ° C. ± 5 ° C. after the laser beam is radiated. Furthermore, the laser processing apparatus 11 is installed in the temperature-controlled room 16 set to air conditioning at 23 ° C., and the ambient temperature of the laser processing apparatus is set to 23 ° C. ± 5 ° C. The XY stage 12 has a stroke that can move between a position where the honeycomb structure 21 is set and taken out, a position where the image is captured by the CCD camera 13, and a position where the laser beam is irradiated. The control device 14 controls the position of the XY stage 12 and takes in the image information from the CCD camera 13 and the movement information of the XY stage 12 at the time of imaging, and the position of the predetermined cell to be plugged and the perforation shape. The laser beam irradiation control and the XY stage 12 position control are performed. The CCD camera 13 has an image resolution sufficient to define the cell shape. Further, the laser light is deflected mechanically or electrically using a galvanometer in the laser head 15 and shaken in the traveling direction. Since the CCD camera 13 images the cell through the masking film 31, the masking film 31 is made to be light transmissive and uses a material and thickness that match the laser light and the plugging material (slurry).

First, the honeycomb structure 21 is prepared. As shown in FIG. 2, the honeycomb structure 21 has an outer diameter of 300 mm and an overall length of 300 mm, the cells 25a and 25b are substantially square, and have an opening dimension (A) of 0.7 to 1.3 mm, and the cells 25a and 25b. Using about 15000 pieces.
Next, the honeycomb structure 21 is set on the XY stage 12, the operation is started from the state where the laser processing apparatus is stopped, and the position of the XY stage is shifted so as not to hit the honeycomb structure, and the laser beam is irradiated with the laser beam. To do. Then, when the temperature of the galvanometer 18 in the laser head 15 of the laser processing apparatus 11 reaches 36 ° C. ± 5 ° C., the irradiation of the laser beam is once terminated, and the XY stage is irradiated so that the laser beam strikes the masking film 31. The position is reset and the masking film is perforated with laser light. As shown in FIG. 4A, the masking film 31 is perforated with laser light so that the area of the perforated hole is 45% or more with respect to the cell opening area. d) is performed at a position of 0.01 to 0.2 mm. When the perforation to the masking film 31 attached to one end face of the honeycomb structure 21 is completed, the top and bottom of the honeycomb structure 21 are reversed and the perforation is similarly performed to the masking film 31 attached to the other end face.
Next, as shown in FIG. 3B, the sticking surface of the masking film 31 is immersed in the plugging material (slurry) 23, and the plugging material (slurry) 23 is filled into the cells 25a from the perforations 32. . Then, as shown in FIG. 3 (c), the plugged material (slurry) 23 after filling is cured and dried, and one end face 22a side is alternately plugged with the plugging material 23a. 21. Similarly, the other end face 22b side is plugged alternately with a plugging material (slurry) 23, and the masking film 31 is further removed to obtain the honeycomb filter 20 shown in FIG.

(Embodiment 2 )
In the laser processing apparatus shown in the second embodiment, the honeycomb structure 21 and the dummy body 40 are prepared. As shown in FIG. 2, the honeycomb structure 21 has an outer diameter of 300 mm and an overall length of 300 mm, the cells 25a and 25b are substantially square, and have an opening dimension (A) of 0.7 to 1.3 mm, and the cells 25a and 25b. Using about 15000 pieces. Further, as the dummy body 40, a defective product of the above-described honeycomb structure 21 with a masking film 31 attached is used.
Next, the dummy body 40 is set on the XY stage 12, and the masking film 31 attached to the dummy body 40 is irradiated with laser light to perforate the masking film. When the temperature of the galvanometer 18 in the laser head 15 of the laser processing apparatus 11 reaches 36 ° C. ± 5 ° C., the irradiation of the laser beam to the dummy body is finished, and the dummy body 40 is taken out from the XY stage 12. Then, the honeycomb structure 21 to which the masking film 31 is adhered is set on the XY stage 12, and the masking film 31 is punched with a laser beam. As shown in FIG. 4A, the masking film 31 is perforated with laser light so that the area of the perforated hole is 45% or more with respect to the cell opening area. d) is performed at a position of 0.01 to 0.2 mm. When the perforation to the masking film 31 attached to one end face of the honeycomb structure 21 is completed, the top and bottom of the honeycomb structure 21 are reversed and the perforation is similarly performed to the masking film 31 attached to the other end face.
Next, as shown in FIG. 3B, the sticking surface of the masking film 31 is immersed in the plugging material (slurry) 23, and the plugging material (slurry) 23 is filled into the cells 25a from the perforations 32. . Then, as shown in FIG. 3 (c), the plugged material (slurry) 23 after filling is cured and dried, and one end face 22a side is alternately plugged with the plugging material 23a. 21. Similarly, the other end face 22b side is plugged alternately with a plugging material (slurry) 23, and the masking film 31 is further removed to obtain the honeycomb filter 20 shown in FIG.

  When the masking film 31 is adhered to the end face of the honeycomb structure 21 and then the laser processing apparatus 11 is operated from a state where the laser processing apparatus is stopped when the laser processing apparatus 11 drills a position corresponding to a predetermined cell of the masking film. The test was carried out under the following conditions. That is, the area ratio of the hole perforated with respect to the cell opening area, the presence or absence of empty irradiation, and the temperature of the galvanometer 18 in the laser head when starting to perforate the masking film 31 attached to the honeycomb structure 21; The ambient temperature of the laser processing apparatus was performed under the conditions shown in Table 1. And after piercing | boring to the masking film 31 stuck to the end surface of the honeycomb structure 21 is complete | finished, the sticking surface of the masking film 31 is immersed in the plugging material (slurry) 23, and plugging material (slurry) After filling the cells, the plugging material 23a is formed by drying. Then, as an evaluation, among the cells that should not be provided with the plugging material, the number of cells in which the plugging material has infiltrated into the adjacent cells and was blocked by the plugging material is counted, The ratio of the total number of cells that should not be provided with a stopper is 0.5% or less (◎), the ratio exceeding 0.5% and 1% or less (○), exceeding 1% Table 1 also shows (Δ) that was 5% or less and (x) that exceeded 5%. Further, the filling property of the plugging material was evaluated by measuring the strength of the plugging material and the cell wall. The bonding strength between the plugging material and the cell wall was measured by pressing a round bar-shaped indenter having a diameter of 1 mm into the plugging material and the indenter was pushed through. And, the one with sufficient bonding strength between the plugging material and the cell wall (◎), the one with sufficient bonding strength between the plugging material and the cell wall and having no problem in practical use (○) The case where the bonding strength between the plugging material and the cell wall was not ensured and could not be used was evaluated as (x).

As shown in Table 1, the ceramic honeycomb filters of Examples 1 to 17 manufactured by the method for manufacturing a ceramic honeycomb filter of the present invention can perforate a masking film at an accurate position, and are provided with a plugging material. It can be seen that the number of cells into which the plugging material penetrates into the cells that should not be present is small. On the other hand, in Comparative Example 1, the area of the hole to be perforated with respect to the cell opening area was less than 45%, and the hole was drilled with the laser beam. The plugging material may come off during use as a honeycomb filter without being fixed, and the PM collection rate may decrease. In Comparative Examples 2 and 3, since the temperature of the galvanometer in the laser head was less than 31 ° C., it can be seen that the number of cells in which the plugging material penetrates into cells that should not be provided with the plugging material is large.

It is a schematic diagram of the laser processing apparatus 11 used by embodiment. An example of a honeycomb filter made of a ceramic base material (hereinafter referred to as “honeycomb filter”) 20 that collects and purifies PM in automobile exhaust gas is shown, (a) is a front view, and (b) is a partial cross section. It is a side view. (A)-(c) is a schematic diagram of a plugging process. (A) is a plan view of a part of the honeycomb structure 21 and masking film 31 of the example after being perforated 32 with a laser LRZ, and (b) is a plugging material (slurry) in the honeycomb structure 21 of the example. ) 33 is a schematic cross-sectional view of a state in which 33 is filled. (A) is a plan view of a part of the honeycomb structure 21 and the masking film 31 of the comparative example after being perforated 32 by the laser LRZ, and (b) is a plugging material ( FIG. 3 is a schematic cross-sectional view of a state in which (slurry) 33 is filled.

Explanation of symbols

11: Laser processing device 12: XY stage 13: CCD camera 14: Control device 15: Laser head 16: Constant temperature chamber 17: Heater 18: Galvanometer 20: Ceramic honeycomb filter (honeycomb filter)
21: Ceramic honeycomb structure (honeycomb structure)
21a: outer peripheral wall 22a, 22b: end face 23: plugging material (slurry)
23a, 23b: plugging material 24: cell wall 25a, 25b: cell 31: masking film 32: perforation 34: plugging material (slurry) that has entered into adjacent cells
40: Dummy body A: Width across flats b: Clearance

Claims (3)

A position corresponding to a predetermined cell of the masking film by laser light emitted from a laser head of a laser processing apparatus after a masking film is attached to an end face of a ceramic honeycomb structure having a large number of cells partitioned by cell walls Manufacturing of a ceramic honeycomb filter in which the bonding surface of the masking film is immersed in a plugging material, the plugging material is filled into the predetermined cells from the holes, and plugged. In the method, when 45% or more of the cell area is perforated at a predetermined position of the masking film by the laser beam, the laser beam is irradiated with the laser beam, and the temperature of the galvanometer in the laser head is set to 36 ± 5. The masking film adhered to the ceramic honeycomb structure is perforated with the laser beam at a temperature of ° C. Method for producing a ceramic honeycomb filter. 2. The method for manufacturing a ceramic honeycomb filter according to claim 1, wherein the laser beam is perforated with the laser beam at an ambient temperature of 23 ° C. ± 5 ° C. 3. The dummy body is irradiated with the laser beam, the temperature of the galvanometer in the laser head is set to 36 ± 5 ° C., and the masking film bonded to the ceramic honeycomb structure is punched with the laser beam. The manufacturing method of the ceramic honeycomb filter of Claim 1 or Claim 2 .

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