JP4878699B2 - Method for producing alumina fiber assembly - Google Patents

Description

【００６２】
表１に示した結果から明らかなように、実施例１に係るアルミナ短繊維の平均強度は６．３×１０^−４Ｎであり、その標準偏差は１．８８であるのに対し、比較例１に係るアルミナ短繊維の平均強度は５．０×１０^−４Ｎであり、その標準偏差は２．１６であった。即ち、実施例１に係るアルミナ短繊維の平均強度及びばらつきは、共に比較例１に係るアルミナ短繊維の平均強度及びばらつきよりも優れたものであった。
【００６３】
また、実施例１に係る面圧測定用サンプルの初期面圧は１４５ｋＰａ、耐久後面圧は１０２ｋＰａであるのに対し、比較例１に係る面圧測定用サンプルの初期面圧は１４０ｋＰａであり、耐久後面圧は９１ｋＰａであり、いずれの面圧も、実施例１に係るサンプルの方が好適な結果であった。
また、面圧測定用サンプルの経時劣化率も実施例１に係るサンプルの方が良好な結果を示した。
【００６４】
さらに、実施例１に係るアルミナ短繊維の切断面には欠け、ばり及びマイクロクラックは観察されなかったが、比較例１に係るアルミナ短繊維の切断面には多数の欠け、ばり及びマイクロクラックが観察された。
【００６５】
【発明の効果】
以上の説明した通り、本発明のアルミナ繊維集合体の製造方法によると、アルミナ繊維集合体に用いられるアルミナ短繊維の強度は優れたものとなり、そのばらつきも小さなものとなる。従って、初期面圧が高く、経時劣化を起しにくいアルミナ繊維集合体を製造することができる。
【図面の簡単な説明】
【図１】ハニカムフィルタの一例を模式的に示した斜視図である。
【図２】（ａ）は、図１に示したハニカムフィルタを構成する多孔質セラミック部材の一例を模式的に示した斜視図であり、（ｂ）は、そのＡ−Ａ線断面図である。
【図３】保持シール材の一例を模式的に示した平面図である。
【図４】（ａ）は、本発明のアルミナ繊維集合体の製造方法により製造したアルミナ繊維集合体に用いられているアルミナ短繊維の切断面のＳＥＭ写真であり、（ｂ）は、従来の方法により製造したアルミナ繊維集合体に用いられているアルミナ短繊維の切断面のＳＥＭ写真である。
【符号の説明】
１０ ハニカムフィルタ
１３ シール材層
１４ 接着層
１５ セラミックブロック
２０ 多孔質セラミック部材
２１ 充填材
２２ 貫通孔
２３ 隔壁
３０ 保持シール材
３１ 基材部
３２ 凸状合わせ部
３３ 凹状合わせ部[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing an alumina fiber aggregate in which short alumina fibers are formed into a mat shape.
[0002]
[Prior art]
Recently, it has been a problem that particulates contained in exhaust gas discharged from internal combustion engines such as vehicles such as buses and trucks and construction machinery cause harm to the environment and the human body.
Various ceramic filters that purify exhaust gas by collecting particulates in the exhaust gas by passing the exhaust gas through a porous ceramic have been proposed.
[0003]
As such a ceramic filter, for example, a plurality of porous ceramic members 20 as shown in FIG. 1 are bound together via an adhesive layer 14 to form a cylindrical ceramic block 15, and a sealing material layer 13 is formed on the outer periphery thereof. A honeycomb filter 10 in which is formed is used. Further, as shown in FIG. 2, the porous ceramic member 20 has a large number of through holes 22 arranged in parallel in the longitudinal direction, and the partition wall 23 that separates the through holes 22 functions as a filter.
[0004]
That is, as shown in FIG. 2 (b), the through-hole 22 formed in the porous ceramic member 20 is sealed by the filler 21 at either the inlet side or the outlet side end of the exhaust gas, The exhaust gas flowing into one through-hole 22 always flows through the partition wall 23 separating the through-holes 22 and then flows out from the other through-holes 22. When the exhaust gas passes through the partition wall 23, Particulates are captured by the partition wall 23 and the exhaust gas is purified.
Moreover, the sealing material layer 13 is formed in the outer peripheral portion, and is formed to prevent the exhaust gas from leaking from the through hole 22 exposed to the outside of the porous ceramic member 20 whose part is cut. .
[0005]
As a non-oxide ceramic material that constitutes such a porous ceramic member 20, silicon carbide is extremely excellent in heat resistance and easy to recycle, so it is used in various large vehicles, vehicles equipped with diesel engines, etc. Has been.
[0006]
The exhaust gas contains CO, NOx, HC and the like in addition to the particulates, and has the same shape as the honeycomb filter 10 described above in order to remove these substances from the exhaust gas. Therefore, an exhaust gas purifying catalytic converter in which a catalyst such as platinum is supported has been proposed.
[0007]
Furthermore, recently, research on the next clean power source that does not use oil as a power source is underway, and a particularly promising one is, for example, a fuel cell.
A fuel cell uses electricity obtained when hydrogen and oxygen react to produce water as a power source, but oxygen is taken out directly from the air, but hydrogen is methanol, gasoline, etc. When reforming methanol, gasoline, etc., a fuel cell catalytic converter having the same shape as the honeycomb filter 10 and carrying a copper catalyst is used. ing.
[0008]
Such a honeycomb filter 10, an exhaust gas purification catalytic converter, a fuel cell catalytic converter, and the like are usually disposed and used in a cylindrical metal shell. A gap exists between the catalytic converter and the catalytic converter for the fuel cell and the metal shell, and a holding sealing material 30 as shown in FIG. 3 is interposed to fill the gap.
[0009]
As shown in FIG. 3, the holding sealing material 30 is provided with a convex matching portion 32 on one short side of a substantially rectangular base material portion 31 and a concave matching portion 33 on the other short side. .
When the holding sealing material 30 is wound around the outer periphery of the honeycomb filter 10 or the like, the convex matching portion 32 and the concave matching portion 33 are just fitted to each other. As a result, the holding sealing material 30 is displaced. It is supposed not to.
[0010]
In order to manufacture the holding sealing material 30, first, an alumina fiber stock solution (alumina-silica fiber stock solution) is spun by a melting method to produce a continuous long fiber precursor, and this continuous long fiber precursor is fired. Alumina long fiber is produced.
Next, the alumina long fibers are cut into alumina short fibers, and then the alumina short fibers are collected, opened and laminated, and then pressed to produce a mat-like alumina fiber aggregate.
And the holding sealing material 30 was manufactured by punching this mat-like fiber assembly into a predetermined shape.
[0011]
The holding sealing material 30 manufactured in this way is wound around the outer peripheral surfaces of the honeycomb filter 10, the exhaust gas purification catalytic converter, the fuel cell catalytic converter, etc., and then accommodated in a metal shell. In such an accommodation state, since the holding sealing material 30 is compressed in the thickness direction, a repulsive force (surface pressure) against the compressive force is generated in the holding sealing material 30. The repulsive force acts to hold the honeycomb filter 10, the exhaust gas purifying catalytic converter, the fuel cell catalytic converter, and the like in the metal shell.
[0012]
When the honeycomb shell 10, the exhaust gas purifying catalytic converter, the fuel cell catalytic converter, and the like are housed in the metal shell by a press-fitting method, a metal cylindrical member having an O-shaped cross section is used. When accommodated in the inside, a clamshell obtained by dividing a metal cylindrical member having an O-shaped cross section into a plurality of pieces along the axial direction is used. In addition, a metal shell that uses a metal cylindrical member having a C-shaped or U-shaped cross section and is fastened by welding, bonding, bolts, or the like is also used.
[0013]
[Problems to be solved by the invention]
However, the alumina fiber aggregate produced by the conventional production method is not sufficiently high in mechanical strength of the alumina short fibers used in the alumina fiber aggregate, and the variation was relatively large. The initial surface pressure of the alumina fiber aggregate cannot be said to be sufficient, and the surface pressure degradation of the alumina fiber aggregate may be relatively large with time, and there is still room for improvement.
Here, the “initial surface pressure” means the surface pressure of the alumina fiber aggregate that has just been manufactured and is not subjected to load or heat.
[0014]
The present invention has been made in order to solve the above-mentioned problems. Since the strength of the short alumina fibers is high and the variation thereof is small, the alumina fiber assembly is sufficiently high in initial surface pressure and hardly deteriorates with time. It aims at providing the manufacturing method of a body.
[0015]
[Means for Solving the Problems]
The method for producing an alumina fiber assembly of the present invention includes a spinning step of obtaining a continuous long fiber precursor using an alumina fiber stock solution used in an inorganic salt method as a material,
A chop process for cutting the continuous long fiber precursor to become a short fiber precursor,
A mat production step of producing a mat-like short fiber precursor using the obtained short fiber precursor,
And firing the mat-like short fiber precursor to produce an alumina fiber aggregate.
Hereinafter, the present invention will be specifically described by way of embodiments.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
The method for producing an alumina fiber assembly of the present invention includes a spinning step of obtaining a continuous long fiber precursor using an alumina fiber stock solution used in an inorganic salt method as a material,
A chop process for cutting the continuous long fiber precursor to become a short fiber precursor,
A mat production step of producing a mat-like short fiber precursor using the obtained short fiber precursor,
And firing the mat-like short fiber precursor to produce an alumina fiber aggregate.
[0017]
The method for producing an alumina fiber aggregate of the present invention has sufficient mechanical strength of the alumina short fibers used in the alumina fiber aggregate to be produced by performing the firing process after the spinning process, the chop process and the mat manufacturing process. Along with the increase, the dispersion is reduced, an alumina fiber assembly having a high initial surface pressure and a small deterioration of the surface pressure with time is produced.
This is considered to be due to the following reasons.
[0018]
That is, the alumina short fiber used in the alumina fiber aggregate produced by the conventional method is obtained by calcining the continuous long fiber precursor obtained by spinning the alumina fiber stock solution to produce the alumina long fiber, and then the alumina long fiber. The fiber is produced by cutting by a mechanical means such as a cutter. However, some of the alumina short fibers produced in this manner had a flash on the cut surface ( (Refer FIG.4 (b)).
FIG. 4A is an SEM photograph of the cut surface of the alumina short fiber used in the alumina fiber aggregate produced by the method for producing an alumina fiber aggregate of the present invention, and FIG. It is a SEM photograph of the cut surface of the alumina short fiber used for the alumina fiber aggregate manufactured by the method.
[0019]
When cutting the alumina long fiber, before the cutter or the like completely cut the alumina long fiber, a part of the alumina long fiber in the vicinity of the cut surface may be chipped. By adhering to, it becomes a flash on the cut surface of the alumina short fiber as shown in FIG.
[0020]
When the alumina long fiber is cut by a mechanical means such as a cutter, a large shear stress acts on the cut surface. However, since the alumina long fiber is made of a hard and brittle ceramic having a certain strength, a part of the alumina long fiber is chipped due to the shear stress acting on the cut surface, and the chip of the chip It is considered that the state where the sticking to the cut surface is the flash as shown in FIG.
[0021]
In addition, many alumina short fibers used in the alumina fiber aggregate are in an intricately intertwined state, but when the flash is generated on the cut surface of the alumina short fibers, the alumina short fibers are Intricately intertwining each other damages other alumina short fibers.
[0022]
Further, when the alumina short fibers are observed in detail, there are portions where microcracks are generated due to the chipping and flashing, and microcracks are also generated in other portions due to the force applied to the fibers during cutting. There is a part.
Therefore, it is considered that the mechanical strength of the short alumina fibers does not become sufficiently high due to such chips, flashes, microcracks, and the like, and the variation becomes large.
[0023]
In addition, the initial surface pressure and temporal deterioration of the surface pressure of the alumina fiber aggregate depend on the mechanical strength of the alumina short fiber used in the alumina fiber aggregate, and the mechanical strength of the alumina short fiber is excellent. Then, the initial surface pressure of the alumina fiber aggregate is sufficiently high, and the surface pressure deterioration with time is small.
However, as described above, in the conventional alumina fiber aggregate, the mechanical strength of the alumina short fibers used in the alumina fiber aggregate is not sufficiently high, and variation thereof is large. It is considered that the initial surface pressure of the fiber assembly was not sufficiently high, and the surface pressure was deteriorated with time.
[0024]
In the method for producing an alumina fiber aggregate of the present invention, the continuous fiber precursor obtained in the spinning process is cut with a cutter or the like without subjecting it to a firing treatment, thereby producing a short fiber precursor. That is, since the continuous long fiber precursor is only subjected to a drawing process after spinning, it is soft, and even if the continuous long fiber precursor is cut with a cutter or the like, it is caused by shear stress acting on the cut surface. Thus, no chipping occurs in the vicinity of the cut surface (see FIG. 4A). Further, microcracks are hardly generated on the cut surface.
Therefore, the alumina short fiber used for the alumina fiber aggregate to be manufactured thereafter has sufficiently high mechanical strength as compared with the alumina short fiber used for the alumina fiber aggregate manufactured by the conventional method. The variation is small. Therefore, it is considered that the alumina fiber aggregate produced by the method for producing an alumina fiber aggregate of the present invention has a high initial surface pressure and is unlikely to deteriorate with time.
[0025]
Hereinafter, the manufacturing method of the alumina fiber aggregate of the present invention will be described in more detail.
In the method for producing an alumina fiber aggregate of the present invention, first, a spinning process is performed to obtain a continuous long fiber precursor using an alumina fiber stock solution used in the inorganic salt method as a material.
[0026]
In this spinning step, first, an alumina fiber stock solution used in the inorganic salt method is prepared.
The alumina fiber stock solution is prepared by an inorganic salt method. Specifically, it is desirable to prepare by mixing silica sol with an aluminum salt aqueous solution. This is because an alumina fiber having high strength can be obtained.
[0027]
As the aluminum salt aqueous solution, for example, an aqueous solution of a basic aluminum salt can be selected. Moreover, the aluminum salt aqueous solution which is an alumina source is also a component for giving viscosity to the said alumina fiber undiluted | stock solution.
[0028]
The mixing ratio of the aluminum salt aqueous solution and the silica sol in the alumina fiber stock solution is desirably 40 to 100% by weight of alumina and 0 to 60% by weight of silica in terms of alumina and silica.
[0029]
Moreover, you may add an organic polymer to such an alumina fiber stock solution as needed. This is because spinnability can be imparted to the alumina fiber stock solution.
[0030]
Examples of the organic polymer include chain polymers containing carbon such as PVA (polyvinyl alcohol), but other low molecular weight compounds that do not have a chain structure as long as they contain carbon. (Not a polymer).
[0031]
Next, the obtained spinning stock solution is concentrated under reduced pressure to obtain an alumina fiber stock solution adjusted to a concentration, temperature, viscosity and the like suitable for spinning. The alumina fiber stock solution prepared by the method as described above usually has a concentration of about 20% by weight, but it is desirable to concentrate it to about 30 to 40% by weight. Further, the viscosity of the alumina fiber stock solution after concentration under reduced pressure is preferably 1 to 200 Pa · s (10 to 2000 P).
[0032]
And the raw material fiber which has a cross-sectional shape similar to the opening shape of a nozzle is continuously obtained by discharging the prepared alumina fiber undiluted solution from the nozzle of a spinning device in a high-speed air current by a dry pressure spinning method or the like. A continuous long fiber precursor is obtained by winding the raw material fibers thus spun in order while being drawn.
[0033]
The opening shape of the nozzle is not particularly limited, and for example, an arbitrary shape such as a perfect circle, a triangle, a Y shape, or a star shape can be selected.
In addition, it is desirable that the raw material fiber in the spun state is drawn about 100 to 200 times to obtain a continuous long fiber precursor. This is because alumina fibers having suitable strength can be produced. In this case, when the cross-sectional shape of the continuous long fiber precursor is a perfect circle, the average fiber diameter is desirably 3 to 25 μm, and more desirably 5 to 15 μm.
[0034]
Moreover, it is desirable to perform a crimping process that imparts crimps to the continuous long fiber precursor. This is because when the short alumina fibers are formed into a mat shape in the subsequent mat manufacturing process, the short alumina fibers can be suitably entangled with each other.
[0035]
Next, the chop process which cut | disconnects the said continuous long fiber precursor so that it may become a short fiber precursor is performed.
In this chopping process, the continuous long fiber precursor is cut to become a short fiber precursor having a length of 0.1 to 100 mm, desirably 2 to 50 mm.
Specifically, a plurality of the continuous long fiber precursors are aligned and cut by a rectangular cutter or the like, and it is desirable to cut the cut surface so that it is flat. If the cut surface of the short fiber precursor has a pointed shape, the cut surface of the alumina short fiber to be manufactured thereafter also has a pointed shape. If such a short fiber precursor or alumina short fiber is sucked, it will have a serious adverse effect on the human body. May be affected.
[0036]
Next, a mat manufacturing step of manufacturing a mat-like short fiber precursor using the obtained short fiber precursor is performed.
[0037]
In this mat manufacturing step, the obtained short fiber precursor is collected, opened and laminated, and then pressed to prepare a mat-like short fiber precursor.
In this mat-like short fiber precursor, the short fiber precursor is in an intertwined state to some extent.
[0038]
The shape of the mat-like short fiber precursor is not particularly limited, but is usually rectangular.
Moreover, the magnitude | size is suitably determined according to the intended purpose of an alumina fiber aggregate.
[0039]
Next, it is desirable to perform needle punching on the mat-like short fiber precursor. This needle punching process allows the upper and lower short fiber precursors to be appropriately entangled by piercing the mat-like short fiber precursor with a needle, and the mat-like short fibers rich in bulkiness and elasticity. It can be a precursor.
[0040]
And the alumina fiber aggregate is manufactured by performing the baking process which bakes the said mat-like short fiber precursor, and manufactures an alumina fiber aggregate, and the manufacturing method of the alumina fiber aggregate of this invention is complete | finished.
[0041]
In this firing step, first, the mat-like short fiber precursor is desirably heated (pretreated) in an oxygen-containing atmosphere at 400 to 600 ° C. for 10 to 60 minutes. This is because the organic components contained in the short fiber precursor used in the mat-like short fiber precursor are removed by combustion.
[0042]
Next, the mat-like short fiber precursor subjected to the above pretreatment is heated to 1000 to 1300 ° C., preferably 1050 to 1250 ° C., for example, in an air atmosphere to sinter the short fiber precursor. When the heating temperature is less than 1000 ° C., the short fiber precursor is likely to be insufficiently sintered, and it becomes difficult to obtain a high strength alumina fiber aggregate. On the other hand, if the heating temperature exceeds 1300 ° C., the alumina fiber aggregate will not be remarkably increased in strength, and productivity and economy will be disadvantageous.
[0043]
In this firing step, the short fiber precursor used for the mat-like short fiber precursor is fired to become an alumina short fiber. However, the short fiber precursor is complicated by the needle punching process described above. These entangled short fiber precursors are bonded to each other by firing. Therefore, the alumina fiber aggregate to be produced has a very excellent mechanical strength.
In addition, the mat-like short fiber precursor fired under such conditions shrinks its volume because the organic component is burned away.
[0044]
Usually, the alumina short fibers are mainly composed of alumina and silica, but the alumina short fibers preferably have a mullite crystal content of 0 to 10% by weight or less. The short alumina fiber having such a chemical composition has excellent heat resistance due to a small amount of amorphous components, and has a high repulsive force when a compressive load is applied. Therefore, when the alumina fiber aggregate according to the present invention is used as a holding sealing material for the honeycomb filter 10 or the like as described in the prior art, it is disposed in the gap between the metal shell and the honeycomb filter 10 or the like. Even when a high temperature is encountered in a state, the generated surface pressure is relatively less likely to decrease.
[0045]
The fiber tensile strength of the alumina short fiber is desirably 1.2 GPa or more, particularly 1.5 GPa or more. The fiber bending strength of the short alumina fibers is preferably 1.0 GPa or more, particularly 1.5 GPa or more. Furthermore, the fracture toughness value of short alumina fibers is 0.8 MN / m ^3/2 Above, especially 1.3MN / m ^3/2 The above is desirable. This is because when the fiber tensile strength, fiber bending strength, and fracture toughness value are increased, the alumina short fiber is extremely strong against tension and bending, and is flexible and difficult to break.
[0046]
Thereafter, the alumina fiber aggregate is processed into a holding sealing material having substantially the same shape as the holding sealing material 30 shown in FIG.
[0047]
The size of the holding sealing material is appropriately determined according to the purpose of use, but the thickness of the holding sealing material is, for example, when used as a holding sealing material wound around the outer periphery of the honeycomb filter 10 shown in FIG. The gap formed by the outer diameter of the honeycomb filter 10 and the inner diameter of the metal shell housing the honeycomb filter 10 is preferably about 1.1 to 4 times, more preferably about 1.5 to 3 times.
When the thickness of the holding sealing material is less than 1.1 times the gap, when the honeycomb filter 10 is accommodated in the metal shell, the holding property of the honeycomb filter 10 cannot be increased, and the honeycomb filter 10 The metal shell may be misaligned or loose. Further, in this case, since a high sealing performance cannot be obtained, the exhaust gas leaks easily from the gap portion, and the exhaust gas purification becomes incomplete. On the other hand, when the thickness of the holding sealing material exceeds 4 times the gap, when the honeycomb filter 10 is accommodated in the metal shell, particularly when the press-fitting method is adopted, It becomes difficult to place in.
[0048]
The bulk density of the holding sealing material after being accommodated in the metal shell is 0.1 to 0.3 g / cm. ³ Desirably, 0.1 to 0.25 g / cm ³ Is more desirable. Bulk density is 0.1g / cm ³ If it is less than 1, the initial surface pressure of the holding sealing material cannot be made sufficiently high, while the bulk density is 0.3 g / cm. ³ Exceeding this increases the amount of short alumina fibers to be used as a material, leading to an increase in manufacturing costs.
[0049]
If necessary, the holding sealing material may be subjected to needle punching, and after impregnating the holding sealing material with an organic binder, the holding sealing material is further compressed in the thickness direction of the holding sealing material. May be. This is because the holding sealing material can be compressed in the thickness direction to be thinned.
As said organic binder, latex, such as acrylic rubber and nitrile rubber, PVA, an acrylic resin, etc. can be mentioned.
[0050]
As described above, the method for producing an alumina fiber assembly according to the present invention is a method for producing a short fiber precursor by cutting a continuous long fiber precursor produced by spinning and stretching an alumina fiber stock solution, and then a mat precursor. And firing the mat precursor to produce an alumina fiber assembly.
According to the method for producing an alumina fiber aggregate of the present invention, the cut surface of the short fiber precursor is not chipped, flashed, or microcracked. After that, through the firing step, the mechanical strength is excellent. Alumina short fibers can be produced.
In other words, since the mechanical strength of the alumina short fibers used in the alumina fiber assembly can be made excellent, an alumina fiber assembly having a sufficiently high initial surface pressure and a small deterioration in surface pressure over time is produced. can do.
【Example】
EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited to these Examples.
[0051]
Example 1
First, a basic aluminum chloride aqueous solution (23.5% by weight), silica sol (20% by weight, silica particle size 15 nm), and polyvinyl alcohol (10% by weight) as a spinnability imparting agent are mixed to prepare a spinning dope. The obtained spinning dope was concentrated under reduced pressure at 50 ° C. using an evaporator to prepare an alumina fiber stock solution having a concentration of 38% by weight and a viscosity of 150 Pa · s (1500 P).
[0052]
The above-mentioned alumina fiber stock solution was continuously ejected into the air from a spinning device nozzle (circular cross section) and wound while being stretched to form a continuous fiber precursor.
[0053]
Next, the short fiber precursor produced by cutting the continuous long fiber precursor into a length of 7.5 mm using a rectangular cutter is spread, collected and laminated, and then pressed to form a mat. A short fiber precursor was prepared.
[0054]
Next, in an electric furnace maintained in air at normal pressure, the mat-like short fiber precursor is heated at 500 ° C. for 30 minutes (pretreatment) to burn off organic components, and then in an atmospheric atmosphere. In addition, an alumina fiber assembly was manufactured by firing at 1250 ° C. for 10 minutes in an electric furnace maintained at normal pressure.
[0055]
The alumina fiber aggregate had an alumina / silica weight ratio of 72:28, the average fiber diameter of the alumina short fibers was 7.3 μm, and the cross-sectional shape was a perfect circle.
[0056]
Comparative Example 1
After producing a continuous long fiber precursor in the same manner as in Example 1, the continuous long fiber precursor was calcined under the same conditions as the firing conditions of Example 1 to produce alumina long fibers. The average fiber diameter of the alumina long fibers was 7.2 μm.
Then, the alumina short fibers produced by cutting the produced alumina long fibers into a length of 5 mm using a rectangular cutter are spread, collected and laminated, and then pressed to form a mat-like alumina fiber aggregate. Was made.
[0057]
Each physical property of the alumina fiber assembly according to Example 1 and Comparative Example 1 was evaluated by the following method, and the results are shown in Table 1 below.
[0058]
(1) Strength of short alumina fiber
The tensile strength of the alumina short fiber used for the alumina fiber assembly according to Example 1 and Comparative Example 1 was measured with a tensile tester. The measurement was carried out on 10 arbitrarily selected alumina short fibers, and the average value was taken as the strength of the alumina short fibers according to Example 1 and Comparative Example 1, and the variation was evaluated by standard deviation.
[0059]
(2) Measurement of surface pressure
The alumina fiber assembly according to Example 1 and Comparative Example 1 is punched into a 25 mm square to obtain a surface pressure measurement sample, and the surface pressure of the surface pressure measurement sample without being sandwiched and heated is referred to as “initial surface pressure”. The surface pressure measurement sample is sandwiched with a dedicated jig, and the bulk density is 0.3 g / cm. ³ Then, it was kept in the atmosphere at 1000 ° C., and the surface pressure after 100 hours was measured as “surface pressure after endurance”.
Further, [100− (post-endurance surface pressure / initial surface pressure) × 100] (%) was calculated, and the surface pressure deterioration rate with time was calculated.
[0060]
(3) Observation of cut surface
The state of the cut surface of the short alumina fibers according to Example 1 and Comparative Example 1 was observed with a scanning electron microscope (SEM), and the presence or absence of chips, flashes, microcracks, and the like were examined.
[0061]
[Table 1]

[0062]
As is clear from the results shown in Table 1, the average strength of the alumina short fibers according to Example 1 is 6.3 × 10. ^-4 N, the standard deviation of which is 1.88, whereas the average strength of the alumina short fibers according to Comparative Example 1 is 5.0 × 10 ^-4 N, and its standard deviation was 2.16. That is, the average strength and variation of the alumina short fibers according to Example 1 were both superior to the average strength and variation of the alumina short fibers according to Comparative Example 1.
[0063]
The initial surface pressure of the surface pressure measurement sample according to Example 1 is 145 kPa and the post-endurance surface pressure is 102 kPa, while the initial surface pressure of the surface pressure measurement sample according to Comparative Example 1 is 140 kPa, which is durable. The rear surface pressure was 91 kPa, and any surface pressure was more favorable for the sample according to Example 1.
Moreover, the sample with respect to the surface pressure measurement showed a better result for the sample according to Example 1 with respect to the deterioration rate with time.
[0064]
Furthermore, no cracks, burrs and microcracks were observed on the cut surfaces of the alumina short fibers according to Example 1, but there were many chips, burrs and microcracks on the cut surfaces of the alumina short fibers according to Comparative Example 1. Observed.
[0065]
【Effect of the invention】
As described above, according to the method for producing an alumina fiber aggregate of the present invention, the strength of the short alumina fibers used in the alumina fiber aggregate is excellent, and the variation is small. Therefore, it is possible to produce an alumina fiber aggregate that has a high initial surface pressure and is unlikely to deteriorate with time.
[Brief description of the drawings]
FIG. 1 is a perspective view schematically showing an example of a honeycomb filter.
2A is a perspective view schematically showing an example of a porous ceramic member constituting the honeycomb filter shown in FIG. 1, and FIG. 2B is a sectional view taken along line AA in FIG. .
FIG. 3 is a plan view schematically showing an example of a holding sealing material.
FIG. 4A is a SEM photograph of a cut surface of an alumina short fiber used in an alumina fiber assembly produced by the method for producing an alumina fiber assembly of the present invention, and FIG. It is a SEM photograph of the cut surface of the alumina short fiber used for the alumina fiber aggregate manufactured by the method.
[Explanation of symbols]
10 Honeycomb filter
13 Sealing material layer
14 Adhesive layer
15 Ceramic block
20 Porous ceramic members
21 Filler
22 Through hole
23 Bulkhead
30 Holding sealing material
31 Substrate part
32 Convex part
33 Concave part

Claims (2)

A spinning step for obtaining a continuous long fiber precursor using an alumina fiber stock solution used in the inorganic salt method as a material;
Chop step of cutting the continuous long fiber precursor to become a short fiber precursor,
A mat production step of producing a mat-like short fiber precursor using the obtained short fiber precursor,
A firing step of firing the mat-like short fiber precursor to produce an alumina fiber aggregate,
In the chopping process, a plurality of the continuous long fiber precursors are aligned, and the cutting surface is flattened by a cutter, and is cut so that there is no chipping, flashing, or microcracking near the cutting surface. A method for producing an alumina fiber assembly. A metal shell comprising: an alumina fiber aggregate produced by the method for producing an alumina fiber aggregate according to claim 1; and a holding sealing material comprising the alumina fiber aggregate is wound around the outer periphery of the honeycomb filter. Manufacturing method.

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