JP2011169325A - Holding and sealing material for catalytic converters, method for producing the same, ceramic fiber assembly and ceramic fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a holding and sealing material for a catalytic converter whose surface pressure is less likely to be deteriorated by aging. <P>SOLUTION: The holding and sealing material 4 for a catalytic converter, which is constituted of ceramic fibers 6 collected in a mat-like shape, is disposed in a gap between a catalyst support 2 and a metallic shell 3 covering the outer periphery of the catalyst support 2. The ceramic fibers are partially bound to one another with a ceramic adhesive 7. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention relates to a holding seal material for a catalytic converter, a method for producing the same, a ceramic fiber assembly, and a ceramic fiber.

Conventionally, an internal combustion engine using gasoline or light oil as a fuel has been used for more than 100 years as a power source for vehicles, particularly automobiles. However, exhaust gas is harmful to health and the environment. Therefore, recently, various exhaust gas purifying catalytic converters for removing CO, NOx, HC and the like contained in exhaust gas, and various DPFs for removing PM and the like have been proposed. A normal exhaust gas purifying catalytic converter includes a catalyst carrier, a metal shell covering the outer periphery of the catalyst carrier, and a holding sealing material disposed in a gap therebetween. As the catalyst carrier, a cordierite carrier formed in a honeycomb shape is used, and a catalyst such as platinum is supported on the carrier.

Recently, research on the next clean power source that does not use oil as a power source has been promoted, and a particularly promising example is a fuel cell. A fuel cell uses electricity obtained when hydrogen and oxygen react to form water as a power source. Oxygen is extracted directly from the air, while hydrogen is reformed from methanol, gasoline, or the like. In this case, reforming of methanol or the like is performed by a catalytic reaction. Also in such a fuel cell, a catalytic converter for a fuel cell including a catalyst carrier, a metal shell covering the outer periphery of the catalyst carrier, and a holding sealing material disposed in a gap therebetween is used. Yes. As the catalyst support, a cordierite carrier formed in a honeycomb shape is used, and a copper-based catalyst is supported on the support.

A method for manufacturing the above catalytic converter will now be briefly described. First, after a ceramic fiber is spun by a melting method or the like, a material is produced by assembling the ceramic fiber into a mat shape. By punching this material with a mold, a belt-like holding sealing material is produced. Next, after winding this holding sealing material around the outer peripheral surface of the catalyst carrier, the catalyst carrier is accommodated in a metal shell. As a result, a desired catalytic converter is completed. Since the holding sealing material is compressed in the thickness direction in such an accommodation state, a repulsive force (surface pressure) against the compressive force is generated in the holding sealing material. The repulsive force acts to hold the catalyst carrier in the metal shell.

However, since the conventional holding sealing material is exposed to high temperatures such as vibration and exhaust gas during use, the surface pressure gradually decreases with time, and the retention and sealing properties of the catalyst carrier are relatively early. There was a drawback that it became worse.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a holding seal material for a catalytic converter in which surface pressure is less likely to deteriorate with time. Another object of the present invention is to provide a production method, a ceramic fiber assembly, and a ceramic fiber suitable for the above-mentioned catalytic converter holding sealing material.

Accordingly, the inventors of the present application have conducted intensive research to solve the above problems. As a result, when an external load that compresses the fiber aggregate is applied for a long time, the ceramic fibers constituting the fiber aggregate slip and shift, which causes a reduction in the surface pressure of the fiber aggregate. Got. Therefore, the inventors of the present application have focused on a region where fibers are closely overlapped with each other, with the expectation that a good result will be obtained if the problem of slippage / deviation between fibers is solved by some means. Then, further studies were made to improve such a part, and finally the present invention was conceived.

That is, the invention according to claim 1 is a holding sealing material that is formed in a gap between a catalyst carrier and a metal shell that covers the outer periphery of the catalyst carrier with ceramic fibers assembled in a mat shape as a constituent element. The gist of the present invention is a catalytic converter holding sealing material in which the ceramic fibers are partially bonded to each other with a ceramic adhesive.

According to a second aspect of the present invention, in the first aspect, the ceramic adhesive is made of a material constituting the ceramic fiber. According to a third aspect of the present invention, in the first aspect, the ceramic fiber is an alumina-silica fiber, and the ceramic adhesive is mainly composed of alumina.

According to a fourth aspect of the present invention, in any one of the first to third aspects, the ceramic adhesive is contained in an amount of 1 to 8% by weight. The invention according to claim 5 is a method for producing the holding seal material for a catalytic converter according to any one of claims 1 to 4, wherein a spinning process for obtaining a precursor fiber using a ceramic fiber spinning solution as a material is provided. A firing step in which the precursor fibers are heated and sintered; a molding step in which the obtained ceramic fibers are three-dimensionally aggregated to form a mat-like aggregate; and the ceramic fibers constituting the aggregate The gist of the present invention is a method for producing a holding sealing material for a catalytic converter, which comprises a bonding step of bonding a ceramic converter with a ceramic adhesive.

According to a sixth aspect of the present invention, in the fifth aspect, in the bonding step, after the raw material solution of the ceramic adhesive is supplied between the ceramic fibers constituting the aggregate, the aggregate is heated to supply the raw material solution. The specific component in the raw material solution was sintered to be ceramicized.

According to a seventh aspect of the present invention, in the fifth aspect of the present invention, in the bonding step, the aggregate is impregnated with the low-viscosity water-soluble metal solution that is the raw material solution, and then the aggregate is dried. The assembly was heated to sinter the metal component in the solution to make it ceramic.

The invention described in claim 8 is that in claim 7, the water-soluble metal solution is supplied in an amount of 1 to 10% by weight of the aggregate. The invention according to claim 9 is the water-soluble metal solution according to any one of claims 6 to 8, wherein the ceramic fiber spinning dope is an alumina-silica fiber spinning dope prepared by an inorganic salt method. Was an aqueous solution containing aluminum ions.

According to a tenth aspect of the present invention, there is provided a method for producing the catalytic converter holding sealing material according to any one of the first to fourth aspects, wherein a spinning process for obtaining a precursor fiber using a ceramic fiber spinning solution as a material, and the precursor A liquid in which a liquid substance that can later become a ceramic adhesive is attached to a molding process in which fibers are gathered three-dimensionally to form a mat-like aggregate, and the precursor fibers that constitute the aggregate are closely adjacent to each other. The gist is a method for producing a holding seal material for a catalytic converter, which includes a substance supplying step and a firing step in which the aggregate is heated to sinter the precursor fiber and the liquid substance.

The invention described in claim 11 is the liquid substance supplying step according to claim 10, wherein the liquid substance supplying step includes an inorganic element contained in the alumina-silica fiber with respect to an aggregate composed of a fiber precursor of alumina-silica fiber. The non-aqueous liquid substance was supplied by spraying.

A twelfth aspect of the present invention is the method according to the tenth or eleventh aspect, further comprising a cutting step of chopping the long fibers of the precursor fiber to a predetermined length between the spinning step and the forming step to obtain short fibers. We decided to carry out.

The gist of the invention described in claim 13 is a ceramic fiber assembly in which three-dimensionally assembled ceramic fibers are partially bonded with a ceramic adhesive.

The gist of the invention described in claim 14 is a ceramic fiber assembly characterized in that the ceramic fiber assembly includes a ceramic fiber having a branched structure. The gist of the invention of claim 15 is a ceramic fiber having a branched structure.

The “action” of the present invention will be described below. According to the first aspect of the present invention, since the bridge is provided in a portion where the ceramic fibers are adjacently overlapped with each other, it is difficult for the fibers to slip and shift. Therefore, even when an external load that compresses the holding sealing material is applied for a long time, it is difficult to cause a reduction in surface pressure. Further, in the holding sealing material of the present invention, since the fibers are partially bonded to each other, the voids in the holding sealing material are not completely filled, and physical properties (elasticity) originally required for the holding sealing material And heat insulation). And since the ceramic adhesive material excellent in heat resistance is used, even if a holding sealing material encounters high temperature at the time of use, the intensity | strength of an adhesion part cannot fall easily.

According to the second aspect of the present invention, since the ceramic adhesive is made of the material constituting the ceramic fiber, the affinity with the fiber is high and the strength of the bonded portion is high. Therefore, it is possible to reliably prevent surface pressure deterioration with time.

According to the invention described in claim 3, since the alumina-silica fiber having a small amount of the amorphous component is used, the heat resistance of the fiber itself is improved, and the deterioration with time of the surface pressure at a high temperature can be reduced. . In addition, since the ceramic adhesive mainly composed of alumina has an extremely high affinity for the alumina-silica fiber, the strength of the bonded portion can be further increased.

According to the fourth aspect of the present invention, by setting the content of the ceramic adhesive within the preferred range, it is possible to increase the strength of the bonded portion while maintaining suitable physical properties of the holding sealing material.

If the content is less than 1% by weight, the fibers may not be firmly bonded to each other. On the other hand, if the content exceeds 8% by weight, the problem relating to the adhesive strength is solved, but the voids in the holding sealing material are likely to be filled, and the suitable physical properties of the holding sealing material may be impaired.

According to the invention described in claim 5, since the firing process and the adhesion process of the precursor fiber are performed separately, it is possible to reliably obtain a ceramic fiber having a good shape as compared with the case where this is performed simultaneously, And the fibers of the said suitable shape can be adhere | attached reliably. Therefore, it is possible to easily and reliably manufacture a holding sealing material in which the surface pressure hardly deteriorates with time.

According to the sixth aspect of the present invention, since the surface tension acts on the raw material solution of the liquid ceramic adhesive, when this is supplied to the assembly, the raw material solution is surely located at the portion where the fibers are close to each other and overlap. Adhere to. By heating in this state, the specific component in the raw material solution adhering to the part is ceramicized, and a bridge is formed between the fibers.

According to the invention described in claim 7, since surface tension acts on the low-viscosity water-soluble metal solution, when the aggregate is impregnated, the solution surely adheres to the portion where the fibers are close to each other and overlap each other. To do. In addition, according to the impregnation, the solution can surely and uniformly enter the inside of the assembly. In this state, the aggregate is first dried to remove water to some extent, and then heated, whereby the metal component in the solution attached to the part is oxidized to become ceramic, and a bridge is formed between the fibers. .

According to the invention described in claim 8, by setting the supply amount of the water-soluble metal solution within the preferable range, it is possible to increase the strength of the bonded portion while maintaining the preferable physical properties of the holding sealing material. .

When the supply amount is less than 1% by weight, the amount of the solution adhering to the site where the fibers are close to each other and overlapping may be insufficient, and the fibers may not be firmly bonded. On the other hand, when the supply amount exceeds 10% by weight, voids in the holding sealing material are likely to be filled with an excessively existing solution, which may impair suitable physical properties of the holding sealing material.

According to the ninth aspect of the present invention, a bridge made of alumina having high affinity with the fibers can be formed between the alumina-silica fibers. Therefore, the strength of the bonded portion is increased and the surface pressure can be prevented from being deteriorated with time. Moreover, since the fiber obtained by the inorganic salt method is a crystalline body, there is an advantage that the strength at a high temperature is higher than that of the amorphous fiber obtained by the melting method. Therefore, it is possible to obtain a holding sealing material with little deterioration with time in surface pressure at high temperatures.

According to the invention described in claim 10, through the firing step, the precursor fiber is converted into ceramic and becomes an alumina-silica fiber. At this time, the portions where the fibers are adjacently overlapped with each other are bonded through a ceramicized liquid substance (that is, a ceramic adhesive). As described above, in the present invention, since the precursor fiber firing step and the adhesion step are performed simultaneously, the number of times of heating can be reduced as compared with the case where this is performed separately. Therefore, the manufacturing cost can be reduced. Therefore, it is possible to efficiently and inexpensively manufacture a holding sealing material in which the surface pressure does not easily deteriorate with time.

According to the invention described in claim 11, by spraying and supplying the non-aqueous liquid material, the liquid material surely enters the inside of the aggregate, and the surface tension acts on the proximity polymerization site between the fibers. Selectively adheres. That is, according to the present invention, a liquid substance that can later become a ceramic adhesive can be reliably attached to the proximity polymerization site. Further, since the liquid substance is non-aqueous, even if it adheres to the precursor fiber of the alumina-silica fiber showing water solubility, the fiber will not be dissolved. Therefore, there is no concern that the precursor fiber is excessively dissolved and the strength of the fiber itself is reduced, and it is not particularly necessary to set precise conditions for preventing overdissolution. Therefore, the holding sealing material can be manufactured relatively easily. And since the said liquid substance contains the inorganic element contained in an alumina- silica type fiber, it has high affinity with a precursor fiber and can adhere | attach fibers reliably with high intensity | strength. Therefore, it is possible to reliably prevent surface pressure deterioration with time.

According to invention of Claim 12, there exists the following effect | action. That is, since the precursor fiber is unsintered and relatively soft, even if it receives an impact during cutting, cracks and the like are unlikely to enter the cutting site. Therefore, the alumina-silica fiber obtained by firing this has a stable end shape and excellent mechanical strength. Therefore, the initial surface pressure can be improved. On the other hand, when the cutting process is carried out after sintering the precursor fiber, cracks are likely to enter the cut portion of the alumina-silica fiber due to impact during cutting. This is because, in general, when a precursor fiber is sintered to become ceramic, it becomes hard, but becomes brittle. Therefore, not only the end shape of the alumina-silica fiber becomes unstable, but also the mechanical strength of the fiber itself is lowered.

According to the invention described in claim 13, since the three-dimensionally assembled ceramic fibers are partially bonded with the ceramic adhesive, the fibers are less likely to slip and shift, and the surface pressure is unlikely to decrease. . Further, in the fiber assembly of the present invention, the fibers are partially bonded to each other, so that all the internal voids are not filled, and elasticity and heat insulation are maintained. And since the ceramic adhesive material excellent in heat resistance is used, even if it encounters high temperature, the intensity | strength of an adhesion part cannot fall easily.

According to the invention described in claim 14, since it is configured to include the ceramic fiber having a branched structure, the fibers are less likely to slip and shift than those not including the ceramic fiber having the branched structure. Less likely to cause pressure drop.

According to the invention described in claim 15, when the ceramic fiber having a branched structure is compared with the one not containing the ceramic fiber having a branched structure, when the three-dimensional assembly is performed, the former is compared with the latter. This makes it difficult for the fibers to slip or shift. For this reason, it is possible to obtain a fiber assembly that is unlikely to cause a decrease in surface pressure.

According to the first to fourth aspects of the present invention, it is possible to provide a holding seal material for a catalytic converter in which surface pressure deterioration is unlikely to occur.

According to invention of Claims 5-12, the manufacturing method suitable for manufacturing said outstanding holding | maintenance sealing material can be provided. According to invention of Claim 13, 14, the ceramic fiber aggregate suitable for said outstanding holding | maintenance sealing material etc. can be provided.

According to the fifteenth aspect of the present invention, it is possible to provide a ceramic fiber suitable for the excellent holding sealing material and the like.

The perspective view of the holding sealing material for catalytic converters of the first embodiment embodying the present invention. The perspective view for demonstrating the manufacturing process of the catalytic converter of the said embodiment. The fragmentary sectional view of the catalytic converter of the embodiment. The principal part expanded sectional view of the ceramic fiber of the said embodiment. The graph which shows the result of the comparative test about an Example and a comparative example. The SEM photograph of the ceramic fiber which comprises a holding sealing material.

[First Embodiment]
Hereinafter, a catalytic converter for an automobile exhaust gas purifying apparatus according to a first embodiment embodying the present invention will be described in detail with reference to FIGS.

The catalytic converter 1 of the present embodiment shown in FIG. 3 is provided in the middle of an exhaust pipe of an engine in an automobile body. Since the distance from the engine to the catalytic converter 1 is relatively short, the exhaust gas having a high temperature of about 700 ° C. to 900 ° C. is supplied to the catalytic converter 1. When the engine is a lean burn engine, the catalytic converter 1 is supplied with exhaust gas having a higher temperature of about 900 ° C. to 1000 ° C.

As shown in FIG. 3, the catalytic converter 1 according to the present embodiment basically includes a catalyst carrier 2, a metal shell 3 that covers the outer periphery of the catalyst carrier 2, and a gap between the two. The holding sealing material 4 is configured.

The catalyst carrier 2 is manufactured using a ceramic material typified by cordierite or the like. The catalyst carrier 2 is a columnar member having a circular cross section. The catalyst carrier 2 is preferably a honeycomb structure having a large number of cells 5 extending along the axial direction. A noble metal catalyst such as platinum or rhodium capable of purifying exhaust gas components is supported on the cell wall. In addition to the cordierite carrier, for example, a honeycomb porous sintered body such as silicon carbide or silicon nitride may be used as the catalyst carrier 2.

As the metal shell 3, for example, when a press-fitting method is employed for assembly, a metal cylindrical member having an O-shaped cross section is used. In addition, as a metal material for forming the cylindrical member, a metal excellent in heat resistance and impact resistance (for example, a steel material such as stainless steel) is preferably selected. When a so-called canning method is employed instead of the press-fitting method, a metal cylindrical member having an O-shaped cross section divided into a plurality of pieces along the axial direction (that is, a clam shell) is used.

In addition, when a winding method is adopted at the time of assembly, for example, a metal cylindrical member having a C-shaped or U-shaped cross section, in other words, a metal having a slit (opening) extending along the axial direction only at one place. A cylindrical member is used. In this case, when the catalyst carrier 2 is assembled, the catalyst carrier 2 fixed with the holding sealing material 4 is placed in the metal shell 3 and the metal shell 3 is wound in this state, and the opening end is joined ( Welding, bonding, bolting, etc.). Joining operations such as welding, bonding, and bolting are similarly performed when the canning method is adopted.

As shown in FIG. 1, the holding sealing material 4 is a long mat-like material, and has a concave mating portion 11 at one end and a convex mating portion 12 at the other end. Yes. As shown in FIG. 2, at the time of winding around the catalyst carrier 2, the convex matching portion 12 is just engaged with the concave matching portion 11.

The holding sealing material 4 of the present embodiment is configured with ceramic fibers (that is, fiber aggregates) gathered in a mat shape as main elements. In the present embodiment, alumina-silica fiber 6 is used as the ceramic fiber. In this case, it is more preferable to use alumina-silica fiber 6 having a mullite crystal content of 0 wt% or more and 10 wt% or less. This is because 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, even when a high temperature is encountered in the state of being arranged in the gap, the generated surface pressure is relatively less likely to decrease.

The chemical composition of the alumina-silica fiber 6 may be 68 wt% to 83 wt% alumina and 32 wt% to 17 wt% silica, specifically, Al ₂ O ₃ : SiO ₂ = 72: 28. Even better.

When alumina is less than 68% by weight or silica exceeds 32% by weight, the heat resistance and the resilience when applying a compression load may not be sufficiently achieved. Similarly, when alumina exceeds 83% by weight or when silica is less than 17% by weight, there is a possibility that improvement in heat resistance and improvement in repulsive force when a compression load is applied cannot be sufficiently achieved.

As schematically shown in FIG. 4, in the case of alumina-silica fibers 6 constituting the holding sealing material 4, the fibers are partially bonded with a ceramic adhesive 7. It can also be understood that a bridge is provided at a site where the fibers are adjacently overlapped. From another viewpoint, it can be understood that the holding sealing material 4 includes the alumina-silica fiber 6 having a branched structure. There is a gap in the holding sealing material 4.

The ceramic adhesive 7 is preferably made of a material constituting a ceramic fiber. This is because the ceramic adhesive 7 has a high affinity with the fiber and the strength of the bonded portion is high, so that it is possible to reliably prevent deterioration of the surface pressure over time. Under such circumstances, in this embodiment, the ceramic adhesive 7 mainly composed of alumina is selected.

The ceramic adhesive 7 is preferably contained in an amount of 1 to 8% by weight, particularly 3 to 7% by weight. If the content is less than 1% by weight, the fibers may not be firmly bonded to each other. On the other hand, when the content exceeds 8% by weight, the problem relating to the adhesive strength is solved, but the voids in the holding sealing material 4 are easily filled, and suitable physical properties of the holding sealing material 4, that is, elasticity and heat insulation. There is a risk that the properties and the like may be impaired.

The average fiber diameter of the alumina-silica fiber 6 is preferably about 3 to 25 μm, and more preferably about 5 to 15 μm. This is because if the average fiber diameter is too small, there is an inconvenience that it is easily sucked into the respiratory system. The average fiber length of the alumina-silica fiber 6 is preferably about 0.1 mm to 100 mm, and more preferably about 2 mm to 50 mm. Further, the tensile strength (relative strength) of the alumina-silica fiber 6 itself is preferably 0.1 GPa or more, particularly 0.5 GPa or more. The cross-sectional shape of the alumina-silica-based fiber 6 may be a perfect circle shape as shown in FIG.

The thickness of the holding sealing material 4 before assembly is about 1.1 to 4.0 times, more preferably 1.5 to 3.0 times the gap between the catalyst carrier 2 and the metal shell 3. It is desirable that the degree. If the thickness is less than 1.1 times, high carrier holding ability cannot be obtained, and the catalyst carrier 2 may be displaced or loose with respect to the metal shell 3. Of course, in this case, since high sealing performance cannot be obtained, the exhaust gas leaks easily from the gap portion, and it becomes impossible to realize high low pollution. If the thickness exceeds 4.0 times, particularly when the press-fitting method is adopted, it becomes difficult to dispose the catalyst carrier 2 on the metal shell 3. Therefore, there is a possibility that the improvement in assemblability cannot be achieved.

Further, GBD (bulk density) of the holding seal material 4 after the ^{assembling, 0.10g / cm 3 ~0.30g / cm} 3, as further will be 0.10g ^/ cm ³ ~0.25g ^/ cm 3 Preferably it is set. If the GBD value is extremely small, it may be difficult to achieve a sufficiently high initial surface pressure. On the other hand, if the GBD is too large, the amount of the alumina-silica fiber 6 to be used as a material increases, which tends to increase the cost.

The initial surface pressure of the holding sealing material 4 in the assembled state is preferably 50 kPa or more, and more preferably 70 kPa or more. This is because if the value of the initial surface pressure is high, it is possible to maintain a suitable holding property of the catalyst carrier 2 even if the surface pressure is deteriorated with time.

The holding sealing material 4 may be subjected to needle punching treatment, resin impregnation treatment, or the like as necessary. This is because the holding sealing material 4 can be compressed in the thickness direction and thinned by performing these treatments.

Next, a procedure for manufacturing the catalytic converter 1 will be described. First, an aluminum salt aqueous solution, silica sol and an organic polymer are mixed to prepare a spinning dope. In other words, a spinning dope is prepared by the inorganic salt method. The aluminum salt aqueous solution as an alumina source is also a component for imparting viscosity to the spinning dope. Note that an aqueous solution of a basic aluminum salt is preferably selected as such an aqueous solution. Silica sol as a silica source is also a component for imparting high strength to the fiber. The organic polymer is a component for imparting spinnability to the spinning dope.

An antifoaming agent or the like may be added to the spinning dope. The chemical composition of the alumina-silica fiber 6 can be controlled to some extent by changing the ratio of the aluminum salt and silica sol.

Subsequently, the obtained spinning dope is concentrated under reduced pressure to obtain a spinning dope prepared to a concentration, temperature, viscosity and the like suitable for spinning. Here, it is preferable to concentrate the spinning stock solution which was about 20% by weight to about 30% to 40% by weight. Moreover, it is good to set a viscosity to 10 poise-2000 poise.

Further, the prepared spinning solution is continuously ejected from the nozzle of the spinning device into the air, and the formed precursor fiber is wound up while being drawn. In this case, for example, a dry pressure spinning method is preferably employed.

Next, the first firing step is performed to ceramicize (crystallize) the precursor fiber, thereby curing the precursor fiber and obtaining the alumina-silica fiber 6. In the firing step, it is desirable to set firing conditions such that the mullite crystal content in the resulting alumina-silica fiber 6 is 10% by weight or less. For example, the firing temperature in the firing step is preferably set to 1000 ° C to 1300 ° C. When the firing temperature is less than 1000 ° C., the precursor fiber cannot be completely dried and sintered, and excellent heat resistance and repulsive force when a high compressive load is applied cannot be reliably imparted to the holding sealing material 4. There is a fear. On the other hand, when the firing temperature exceeds 1300 ° C., mullite crystallization in the alumina-silica fiber 6 tends to proceed. For this reason, it becomes difficult to suppress the mullite crystal content to 10% by weight or less, and it may not be possible to reliably impart excellent heat resistance and repulsive force when a high compressive load is applied to the holding sealing material 4.

Subsequently, the long fibers of the alumina-silica-based fibers 6 obtained through each of the above steps are chopped to a predetermined length using, for example, a guillotine cutter, and shortened to some extent. Thereafter, by collecting, defibrating and laminating short fibers, or by pouring a fiber dispersion obtained by dispersing short fibers into water into a mold and drying them, the mat-like A fiber assembly is obtained. Further, this fiber assembly is punched into a predetermined shape to form a holding sealing material 4.

After the molding step, an adhesive step is performed to bond the short fibers constituting the fiber assembly with the ceramic adhesive 7. Specifically, it is performed as follows. First, a raw material solution of the ceramic adhesive material 7 is prepared and supplied between the short fibers constituting the aggregate. That is, in the first step in the bonding process, a liquid substance supplying process is performed in which a liquid substance that can later become the ceramic adhesive 7 is attached to a portion where the short fibers constituting the aggregate are closely overlapped with each other. In this case, a water-soluble metal solution such as an aluminum chloride aqueous solution is preferably used as the raw material solution. It is also possible to use an aqueous solution of an aluminum salt other than chloride, in other words, an aqueous solution other than an aluminum chloride aqueous solution containing aluminum ions. An aqueous solution containing a metal cation other than aluminum ions, such as a zirconium chloride aqueous solution, a titanium chloride aqueous solution, or a chromium chloride aqueous solution, may be selected.

The water-soluble metal solution is preferably low-viscosity, specifically about 0.1 centipoise to 10 centipoise. This is because the surface tension of the low-viscosity water-soluble metal solution is easy to work, and the adhesion to the site where the short fibers are close to each other and overlap is improved. In addition, if the viscosity is too high, it is difficult to reliably and uniformly enter the solution into the fiber assembly.

The water-soluble metal solution may be supplied in an amount of about 1% to 10% by weight, preferably about 2% to 8% by weight of the fiber assembly. This is because if the supply amount is less than 1% by weight, the amount of the solution adhering to the site where the short fibers are close to each other and overlapping is insufficient, and the short fibers may not be firmly bonded to each other. On the contrary, if the supply amount exceeds 10% by weight, voids in the holding sealing material 4 are likely to be filled with an excessively existing solution, and the suitable physical properties of the holding sealing material 4 may be impaired.

As a method of supplying the raw material solution to the fiber assembly, for example, a method of immersing the fiber assembly in the solution and impregnating the inside, a method of supplying a mist-like solution into the fiber assembly by spraying, or dropping the solution There is a method of supplying the fiber assembly. Of these, the impregnation method is preferred. This is because, according to the impregnation method, the raw material solution can be surely and evenly introduced into the fiber assembly.

After impregnation, the fiber assembly is preferably heated and dried. This is because, by performing heating and drying, excess moisture in the raw material solution is removed to some extent, so that firing in the next step can be performed stably.

Next, the dried fiber assembly is fired again at a high temperature to sinter the metal component in the raw material solution adhering to the adjacent portion between the short fibers to be ceramicized. As a result, a bridge made of the ceramic adhesive 7 is formed at the site, and the short fibers are bonded to each other.

Thereafter, the holding sealing material 4 may be further compression-molded in the thickness direction after impregnating the holding sealing material 4 with an organic binder as necessary. Examples of the organic binder in this case include latex such as acrylic rubber and nitrile rubber, polyvinyl alcohol, acrylic resin, and the like.

Then, the holding sealing material 4 obtained by punching the fiber assembly into a predetermined shape is wound around the outer peripheral surface of the catalyst carrier 2 to fix the organic tape 13. Thereafter, press-fit, canning or winding is performed to complete the desired catalytic converter 1.

Hereinafter, examples and comparative examples of the above embodiment will be described.

(Example)
In the example, a sample for evaluating the surface pressure of the holding sealing material 4 was produced as follows.

First, a basic aluminum chloride aqueous solution (23.5% by weight), silica sol (20% by weight, silica particle size 15 nm), polyvinyl alcohol (10% by weight) and an antifoaming agent (n-octanol) are mixed, and a spinning dope is prepared. Produced. Next, the obtained spinning dope was concentrated under reduced pressure at 50 ° C. using an evaporator to prepare a spinning dope having a concentration of 38% by weight and a viscosity of 1000 poise.

The prepared spinning solution was continuously ejected from the nozzle of the spinning device into the air, and the formed precursor fiber was wound up while being drawn. Further, after heating (pretreatment) the precursor fiber at 250 ° C. for 30 minutes in an electric furnace maintained in an air atmosphere, firing was performed at 1250 ° C. for 10 minutes in the same electric furnace.

As a result, a perfect circular alumina-silica fiber 6 having a mullite crystal content of about 8% by weight, an alumina / silica weight ratio of 72:28, and an average fiber diameter of 9 μm was obtained. Subsequently, the long fibers of the alumina-silica fiber 6 were chopped to a length of 5 mm to make short fibers. Thereafter, the short fibers (about 1.0 g) are dispersed in water, and the obtained fiber dispersion is poured into a molding mold and pressed and dried to obtain a mat-like fiber aggregate having 25 mm squares. It was.

The fiber assembly was impregnated with a 5% by weight low-viscosity aluminum chloride aqueous solution (1 centipoise) for about 1 second to 60 seconds, and then the fiber assembly was heated and dried at 100 ° C. for 10 minutes or more. Furthermore, the dried fiber assembly was fired at a temperature of 1200 ° C. or more for 10 minutes, and a bridge made of the ceramic adhesive 7 mainly composed of alumina was formed in the vicinity of the short fibers. The SEM photograph of FIG. 6 shows the alumina-silica fiber 6 of the present example bonded with the ceramic adhesive 7.

This fiber assembly was used as a surface pressure evaluation sample, and the sample was accommodated in an autograph compression jig. And the surface pressure (MPa) after 1, 10, 100 hours when pressing force was applied to the same sample from the thickness direction to make it 3 mm thick was measured. The results are shown in the graph of FIG.
(Comparative Example) In the comparative example, a surface pressure evaluation sample was basically produced according to the example except that the bonding step was not performed. And the surface pressure measurement test was done like the Example using the autograph. The results are shown in the graph of FIG.
(Test result) According to the graph of FIG. 5, the initial surface pressure value of the example was higher than that of the comparative example. Moreover, the degree of decrease in surface pressure after 100 hours was clearly smaller in the example than in the comparative example.

And about the said Example, after manufacturing the holding | maintenance sealing material 4 by punching out the said fiber assembly further to the predetermined shape, this was wound around the catalyst support body 2, and was press-fit in the metal shell 3. FIG. As the catalyst carrier 2, a cordierite monolith having an outer diameter of 130 mmφ and a length of 100 mm was used. As the metal shell 3, a cylindrical member made of SUS304 having a wall thickness of 1.5 mm, an inner diameter of 140 mmφ, and an O-shaped cross section was used. A test was conducted in which the catalytic converter 1 thus assembled was actually mounted on a 3-liter gasoline engine and operated continuously. As a result, generation of abnormal noise during running and rattling of the catalyst carrier 2 were not recognized.

Therefore, according to the present embodiment, the following effects can be obtained.
(1) In the holding sealing material 4 of the present embodiment, a bridge is provided by a ceramic adhesive 7 at a portion where the short fibers of the alumina-silica fibers 6 are close to each other and overlap. For this reason, it becomes difficult to cause slippage and deviation between short fibers. Therefore, even when an external load that compresses the holding sealing material 4 is applied for a long time, it is difficult to cause a reduction in surface pressure. Further, in this holding sealing material 4, the short fibers are partially bonded to each other, so that all the gaps in the holding sealing material 4 are not filled. Therefore, the physical properties (elasticity, heat insulation, etc.) originally required for the holding sealing material 4 are maintained. Moreover, the ceramic adhesive 7 used as a bridge is excellent in heat resistance. Therefore, even if the holding sealing material 4 encounters a high temperature of about 1000 ° C. during use, the strength of the bonded portion is unlikely to decrease, and from this point, it is difficult to cause a decrease in surface pressure.

(2) In the present embodiment, the alumina-silica fiber 6 is selected, and the ceramic adhesive 7 mainly composed of alumina is selected. That is, the ceramic adhesive 7 is made of a material constituting the alumina-silica fiber 6. For this reason, the affinity with the said fiber is very high, and the intensity | strength of an adhesion part is high. Therefore, according to this combination, it is possible to reliably prevent surface pressure deterioration with time. In addition, since the alumina-silica fiber 6 having excellent heat resistance is used, deterioration of the surface pressure with time at high temperatures can be reduced.

(3) In the present embodiment, the content of the ceramic adhesive 7 is set within the preferred range. Therefore, it is possible to increase the strength of the bonded portion while maintaining suitable physical properties of the holding sealing material 4.

(4) In the present embodiment, when the holding sealing material 4 is manufactured, the precursor fiber firing step and the bonding step are performed separately. More specifically, the bonding step is performed after the precursor fiber firing step. For this reason, compared with the case where both processes are performed simultaneously, the alumina-silica-type fiber 6 with a favorable shape can be obtained reliably, and the alumina-silica-type fiber 6 of the said suitable shape can be adhere | attached reliably. . Therefore, it is possible to easily and reliably manufacture the holding sealing material 4 in which the surface pressure hardly deteriorates with time.
[Second Embodiment]
Next, a second embodiment embodying the present invention will be described. Here, the points different from the first embodiment will be mainly described, and common points will be simply denoted by the same member numbers, and description thereof will be omitted.

Here, the holding sealing material 4 having the above-described configuration is manufactured through the following procedure. First, by performing a spinning process according to the above-described embodiment, a long fiber of a precursor fiber is obtained using a spinning stock solution of alumina-silica fiber 6 as a material. Next, a cutting process is performed, and the long fibers are chopped with a guillotine cutter to shorten the fibers to some extent. Next, the forming process is performed to collect, defibrate, and laminate the short fibers, or the fiber dispersion obtained by dispersing the short fibers in water is poured into the mold and pressed and dried. Thus, a mat-like fiber aggregate is obtained. Next, by performing a liquid substance supply step, a liquid substance that can later become the ceramic adhesive 7 is attached to a portion where the precursor fibers constituting the fiber assembly are closely adjacent to each other. Next, a firing step is performed to heat the fiber assembly to simultaneously sinter the precursor fiber and the liquid material. Finally, the fiber assembly is punched and the holding sealing material 4 is obtained.

That is, in the above embodiment, the liquid substance supplying step is performed at a stage after firing (after the fiber is ceramicized), whereas in this embodiment, this is performed at a stage before firing (of the unsintered precursor fibers). Point) is greatly different.

And the following two methods are mentioned as a specific example of a liquid substance supply process. The first method is characterized in that a liquid substance is supplied by placing a fiber assembly made of a fiber precursor of alumina-silica fiber 6 in a high-humidity environment with a lot of moisture. In this case, the water vapor present in the high-humidity environment surely enters the inside of the fiber assembly and then condenses to become moisture. The moisture selectively adheres to the proximity polymerization site between the fibers by the action of surface tension. Here, the precursor fiber of the alumina-silica fiber 6 is water-soluble. Therefore, due to the adhesion of moisture, the surface of the precursor fiber at the proximity polymerization site is somewhat dissolved. The liquid material generated by such dissolution has substantially the same composition as that of the alumina-silica fiber 6, so that it can substantially become the ceramic adhesive 7 later. Therefore, when firing at 1000 ° C. to 1300 ° C., the precursor fiber and the liquid substance are simultaneously sintered and ceramicized, and a bridge made of the ceramic adhesive 7 is formed between the alumina-silica fibers 6. It becomes a state. In this method, it is necessary to set conditions (for example, the amount of water vapor, processing temperature, processing time, etc.) that do not cause excessive dissolution of the precursor fibers. Therefore, it is necessary to pay attention to over-dissolution when water is directly supplied by spraying or the like.

In the second method, a non-aqueous liquid substance containing an inorganic element contained in the alumina-silica fiber 6 is sprayed on a fiber assembly composed of precursor fibers of the alumina-silica fiber 6 to thereby obtain the substance. It is characterized by supplying. In this case, the sprayed non-aqueous liquid substance surely enters the inside of the fiber assembly, and selectively adheres to the proximity polymerization site between the fibers by the action of the surface tension. Examples of non-aqueous liquid substances include commercially available non-aqueous silicone oils. This is because the silicone oil contains silicon (Si), which is an inorganic element contained in the alumina-silica-based fiber 6, and can substantially become the ceramic adhesive 7 later. Therefore, when firing at 1000 ° C. to 1300 ° C., the precursor fiber and the non-aqueous liquid material are simultaneously sintered and ceramicized, and a bridge made of the ceramic adhesive 7 is formed between the alumina-silica fibers 6. It will be in the state. The ceramic adhesive 7 in this case is silicon oxide (silica: SiO ₂ ). In addition to non-aqueous silicone oil, for example, TEOS (ethyl silicate) dissolved in oil can be used.

Therefore, according to the present embodiment, the following effects can be obtained.
(5) In the manufacturing method of this embodiment, since the precursor fiber firing step and the bonding step are performed at the same time, the number of times of heating is small compared to the manufacturing method of the first embodiment in which this is performed separately. That's it. Therefore, less heat energy is required and the manufacturing cost can be reduced. Therefore, the holding sealing material 4 in which the surface pressure hardly deteriorates with time can be manufactured efficiently and at low cost.

(6) When the first method is employed, a liquid substance that can later become the ceramic adhesive 7 can be reliably attached to the proximity polymerization site. In addition, the liquid substance that is a fiber melt basically has the same composition as the alumina-silica fiber 6. For this reason, the said liquid substance has high affinity with a precursor fiber, and can adhere | attach a fiber reliably with high intensity | strength. Therefore, it is possible to reliably prevent surface pressure deterioration with time.

(7) Even when the second method is employed, a liquid substance that can later become the ceramic adhesive 7 can be reliably attached to the proximity polymerization site. Moreover, a non-aqueous liquid material is used here. For this reason, even if it adheres to the precursor fiber of the alumina-silica fiber 6 exhibiting water solubility, the precursor fiber is not dissolved. Therefore, there is no concern that the strength of the alumina-silica fiber 6 itself is reduced due to excessive dissolution of the precursor fiber, and it is not particularly necessary to set precise conditions for preventing over-dissolution. Therefore, the holding sealing material 4 can be manufactured relatively easily. And since the said liquid substance contains the inorganic element contained in the alumina-silica-type fiber 6, it has high affinity with a precursor fiber and can adhere | attach fibers reliably with high intensity | strength. Therefore, it is possible to reliably prevent surface pressure deterioration with time.

(8) In the manufacturing method of the present embodiment, a cutting step is performed between the spinning step and the molding step, and the long fibers of the precursor fiber are mechanically cut to a predetermined length to obtain short fibers. Yes. In other words, the manufacturing method of the present embodiment is different from the manufacturing method of the first embodiment in which the cutting step is performed after the firing step in that the cutting step is performed before the firing step.

When the cutting process is performed after the precursor fiber is sintered as in the manufacturing method of the first embodiment, the cut portion of the alumina-silica fiber 6 is cracked due to the impact at the time of cutting. Is likely to occur. The reason is that, generally, when precursor fibers are sintered to become ceramic, the precursor fibers become hard, but become brittle. Therefore, not only the end shape of the alumina-silica fiber 6 becomes unstable, but also the mechanical strength of the fiber itself is lowered.

On the other hand, since the precursor fiber is unsintered and relatively soft, even if it receives a mechanical impact during cutting, cracks and the like are unlikely to enter the cutting site. Therefore, the alumina-silica fiber 6 obtained by firing this has a stable end shape and excellent mechanical strength. Therefore, according to this embodiment, the initial surface pressure can be improved. It is considered that the prevention of cracks and the like has also contributed to some extent to the prevention of surface pressure deterioration over time.

Incidentally, the fiber diameter and mechanical strength of the alumina-silica fiber 6 obtained through the production method of the present embodiment and the alumina-silica fiber 6 obtained through the production method of the example in the first embodiment. The test which compares was conducted. The specific test method is as follows.

About the former, ten pieces were arbitrarily sampled from the short fibers cut into a predetermined length and fired to obtain alumina-silica fibers 6. Then, the average value and standard deviation of the fiber diameters of the ten alumina-silica fibers 6 were obtained. As a result, the average value was 7.1 μm, and the standard deviation was 0.74 μm. Further, a conventionally known tensile strength test was performed on the ten alumina-silica fibers 6, and an average value and a standard deviation of absolute strength were obtained. As a result, the average value was 6.19 gf and the standard deviation was 1.88 gf. Moreover, the average value and standard deviation of relative strength were calculated | required from the data of the said tensile strength test. As a result, the average value was 1.40 GPa and the standard deviation was 0.45 GPa.

About the latter, ten pieces were arbitrarily extracted from the short fibers obtained by cutting the long fibers of the baked alumina-silica fibers 6 into a predetermined length. Then, the average value and standard deviation of the fiber diameters of the ten alumina-silica fibers 6 were obtained. As a result, the average value was 7.2 μm, and the standard deviation was 0.52 μm. Further, a conventionally known tensile strength test was performed on the ten alumina-silica fibers 6, and an average value and a standard deviation of absolute strength were obtained. As a result, the average value was 4.86 gf and the standard deviation was 2.16 gf. Moreover, the average value and standard deviation of relative strength were calculated | required from the data of the said tensile strength test. As a result, the average value was 1.22 GPa and the standard deviation was 0.61 GPa.

When the above results are summarized, it can be seen that the alumina-silica-based fiber 6 of the present embodiment is not only excellent in mechanical strength but also its variation is small as compared with the example of the first embodiment. Therefore, if the alumina-silica-based fiber 6 obtained in this way is used, the holding sealing material 4 with uniform quality can be obtained.

(9) Moreover, according to the manufacturing method of the present embodiment, since the object to be cut is a precursor fiber that is not so hard, damage and wear of the blade of the guillotine cutter that is a mechanical cutting device are reduced. Therefore, it is not necessary to frequently replace the deteriorated blade, and an increase in running cost can be prevented. In addition, since it is not necessary to make the blade so hard, a general-purpose blade can be used, and an increase in equipment cost can be prevented.

In addition, you may change embodiment of this invention as follows.
Instead of the alumina-silica fiber 6 exemplified in the above embodiment, the holding sealing material 4 may be produced using other ceramic fibers such as crystalline alumina fiber, silica fiber and the like.

The ceramic adhesive 7 may be made of a material that does not constitute a ceramic fiber. For example, when the alumina-silica fiber 6 is selected, the ceramic adhesive 7 made of zirconia, titania, yttria, ceria, calcia, magnesia or the like may be used.

Instead of the basic aluminum chloride aqueous solution used in the above-described example of the first embodiment, for example, the bonding step can be performed by diverting the alumina-silica fiber spinning stock solution itself used in this example. Even in this case, the ceramic adhesive 7 made of a fiber constituent material can be obtained.

As the catalyst carrier 2, a cordierite carrier formed into a honeycomb shape as in the embodiment may be used, and for example, a honeycomb porous sintered body such as silicon carbide or silicon nitride may be used.

When the second method is adopted in the second embodiment, a method instead of spraying when supplying the non-aqueous liquid material, for example, dipping may be adopted. Of course, it is allowed to vaporize and supply the non-aqueous liquid material.

In the embodiment, an example in which the holding sealing material 4 of the present invention is used for the catalytic converter 1 for an exhaust gas purifying apparatus has been shown. Of course, the holding sealing material 4 of the present invention is allowed to be used in other than the exhaust gas purifying device catalytic converter 1, such as a diesel particulate filter (DPF), a fuel cell reformer catalytic converter, and the like.

Next, in addition to the technical ideas described in the claims, the technical ideas grasped by the embodiment described above are listed below.
(1) In Claim 9, the aqueous solution containing the aluminum ions is a basic aluminum chloride aqueous solution or the alumina-silica fiber spinning dope.

(2) In Claim 7 or 8, the water-soluble metal solution is an aqueous solution containing at least one selected from aluminum chloride, zirconium chloride, titanium chloride and chromium chloride.

DESCRIPTION OF SYMBOLS 1 ... Catalytic converter, 2 ... Catalyst support body, 3 ... Metal shell, 4 ... Holding sealing material for catalytic converters, 6 ... Alumina-silica type fiber as ceramic fiber, 7 ... Ceramic adhesive material.

Claims (15)

A holding sealing material having ceramic fibers assembled in a mat shape as a constituent element and disposed in a gap between a catalyst carrier and a metal shell covering the outer periphery of the catalyst carrier, wherein the ceramic fibers are ceramic adhesives. A holding sealing material for a catalytic converter, which is partially bonded. The said ceramic adhesive material consists of the substance which comprises the said ceramic fiber, The holding sealing material for catalytic converters of Claim 1 characterized by the above-mentioned. The said ceramic fiber is an alumina-silica type fiber, The said ceramic adhesive material has an alumina as a main component, The holding sealing material for catalytic converters of Claim 1 characterized by the above-mentioned. 4. The holding sealing material for a catalytic converter according to claim 1, wherein the ceramic adhesive is contained in an amount of 1 to 8% by weight. 5. A method for producing a holding seal material for a catalytic converter according to any one of claims 1 to 4, wherein a spinning process for obtaining a precursor fiber from a ceramic fiber spinning stock solution is heated, and the precursor fiber is heated. A sintering step, a molding step of three-dimensionally gathering the obtained ceramic fibers to form a mat-like aggregate, and an adhesion step of bonding the ceramic fibers constituting the aggregate with a ceramic adhesive The manufacturing method of the holding | maintenance sealing material for catalytic converters characterized by including these. In the bonding step, after the raw material solution of the ceramic adhesive is supplied between the ceramic fibers constituting the aggregate, the specific component in the raw material solution is sintered and ceramicized by heating the aggregate. The method for producing a holding seal material for a catalytic converter according to claim 5, wherein: In the bonding step, the assembly is impregnated with a low-viscosity water-soluble metal solution that is the raw material solution, and then the assembly is dried, and the assembly is further heated to remove the metal component in the solution. 6. The method for producing a holding seal material for a catalytic converter according to claim 5, wherein the ceramic is sintered to be ceramicized. The method for producing a holding seal material for a catalytic converter according to claim 7, wherein the water-soluble metal solution is supplied in an amount of 1 to 10% by weight of the aggregate. 9. The ceramic fiber spinning dope is an alumina-silica fiber spinning dope prepared by an inorganic salt method, and the water-soluble metal solution is an aqueous solution containing aluminum ions. A method for producing a holding seal material for a catalytic converter according to claim 1. A method for producing a holding seal material for a catalytic converter according to claim 1, wherein a spinning process for obtaining a precursor fiber using a ceramic fiber spinning stock solution as a material, and the precursor fiber are assembled three-dimensionally. A molding step for forming a mat-like aggregate, a liquid substance supplying step for adhering a liquid substance that can later become a ceramic adhesive to a portion where the precursor fibers constituting the aggregate are closely overlapped with each other, and the aggregate A method for producing a holding seal material for a catalytic converter, comprising a firing step of heating and sintering the precursor fiber and the liquid substance. In the liquid substance supplying step, a non-aqueous liquid substance containing an inorganic element contained in the alumina-silica fiber is sprayed and supplied to an aggregate composed of a fiber precursor of alumina-silica fiber. The manufacturing method of the holding | maintenance sealing material for catalytic converters of Claim 10 to do. The catalyst according to claim 10 or 11, wherein a cutting step of chopping the long fibers of the precursor fibers to a predetermined length to obtain short fibers is performed between the spinning step and the forming step. Manufacturing method of holding sealing material for converter. A ceramic fiber assembly characterized in that three-dimensionally assembled ceramic fibers are partially bonded with a ceramic adhesive. A ceramic fiber assembly comprising a ceramic fiber having a branched structure. Ceramic fiber having a branched structure.

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