JP2004124721A - Holding material for catalytic converters - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a holding material for a catalytic converter formed from an expansion mat and capable of restricting the lowering of the foaming temperature and the lowering of the surface pressure due to heating with the catalytic carrier held, and capable of stably maintaining the catalytic carrier holding performance and a sealing performance. <P>SOLUTION: This holding material to be used for the catalytic converter, which is provided with the catalytic carrier, a casing for housing the catalytic converter and the holding material wound around the catalytic converter for installation and to be interposed in a clearance between the catalytic carrier and the casing, contains the inorganic fibers, a binder and a calcined vermiculite previously shrunken by calcination. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a catalyst converter holding material (hereinafter, also referred to as a “holding material”) for holding a catalyst carrier used in an exhaust gas purifying catalytic converter of an automobile or the like in a casing.
[0002]
[Prior art]
As is well known, vehicles such as automobiles are equipped with an exhaust gas purifying catalytic converter in order to remove harmful components such as carbon monoxide, hydrocarbons and nitrogen oxides contained in the exhaust gas of the engine. I have. Such a catalytic converter is generally mounted on the catalyst carrier 1, as shown in a cross-sectional view in FIG. And a holding member 3 interposed in a gap between the catalyst carrier 1 and the casing 2.
[0003]
As the catalyst carrier 1, for example, a carrier in which a noble metal catalyst or the like is supported on a cylindrical honeycomb formed body made of cordierite or the like is generally used. The material 3 has a function of safely holding the catalyst carrier 1 so that the catalyst carrier 1 does not collide with the casing 2 due to vibration or the like while the automobile is running, and a function of unpurifying the catalyst carrier 1 from the gap between the catalyst carrier 1 and the casing 2. It is necessary to have a function of sealing so that the exhaust gas does not leak.
[0004]
Conventionally, so-called mat-type holding materials, in which inorganic fibers such as alumina fibers, mullite fibers, or other ceramic fibers are assembled to a predetermined thickness using an organic binder to have appropriate elasticity, have been widely used. Have been. Further, vermiculite, which is a foaming agent, is blended with an inorganic fiber or an organic binder, and the vermiculite is foamed by heating to increase the surface pressure of the holding material, thereby improving the holding force and sealing performance (for example, And Patent Document 1).
[0005]
In a catalytic converter equipped with a holding material containing vermiculite as described above (hereinafter, also referred to as an "expandable mat holding material"), the engine is mounted on an exhaust pipe of an engine and then operated. The exhaust gas is circulated, and the vermiculite is foamed by utilizing the heat of the exhaust gas at that time, so that a sufficient surface pressure for holding the catalyst carrier is applied to the holding material. Therefore, the exhaust gas needs to have a high temperature of 500 ° C. or higher, which is the foaming temperature of vermiculite. In particular, it takes time for the exhaust gas temperature to reach 500 ° C. or higher in a diesel vehicle. May be damaged.
[0006]
Therefore, it has been attempted to foam vermiculite at a lower temperature. For example, it is known that a foaming temperature can be lowered to about 300 ° C. by a method of performing a chemical treatment using ammonium phosphate.
[Patent Document 1]
Japanese Patent Publication No. 2-55389 (pages 3 to 5)
[0007]
[Problems to be solved by the invention]
However, it is known that when the above-mentioned inflatable mat holding material is heated under a load, the surface pressure temporarily decreases. Therefore, even after the vermiculite is foamed and the necessary surface pressure is applied to the holding material, the surface pressure is reduced by the heat of the exhaust gas every time the operation is performed, and this greatly affects the holding performance and the sealing performance of the catalyst carrier. . This also occurs when low-temperature foaming with ammonium phosphate is performed.
[0008]
In a diesel vehicle with strict exhaust gas regulations, the catalyst carrier is held at a higher surface pressure because the catalyst carrier is large and heavy. However, as the surface pressure increases, the degree of decrease in the surface pressure due to heating increases, and such a problem becomes more important.
[0009]
Accordingly, an object of the present invention is to provide a foamable mat that suppresses a decrease in surface pressure due to heating in a state in which the catalyst carrier is held, and can stably maintain the catalyst carrier holding performance and sealing performance. To provide a catalyst converter holding material.
[0010]
[Means for Solving the Problems]
As a result of repeated studies by the present inventors to achieve the above object, untreated vermiculite is gradually dehydrated by heating, for example, shrinks by about 3% by volume at 350 ° C. Of the holding material manufactured using vermiculite that has been somewhat shrunk by baking, has found that the shrinkage during heating is small, and it is possible to suppress a decrease in the surface pressure, and thus complete the present invention. Reached.
[0011]
That is, in order to achieve the above object, the present invention includes a catalyst carrier, a casing containing the catalyst carrier, and a holding material wound around the catalyst carrier and interposed in a gap between the catalyst carrier and the casing. The holding material used for a catalytic converter, wherein the holding material contains inorganic fibers, a binder, and calcined vermiculite which has been shrunk in advance by calcining.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail.
[0013]
The holding material of the present invention has inorganic fibers, a binder, and vermiculite as a foaming agent as main components similarly to the conventional expansion type mat holding material. However, vermiculite used is contracted as described later.
[0014]
As the inorganic fibers, various inorganic fibers conventionally used for a holding material can be used. For example, alumina fibers, mullite fibers, or other ceramic fibers can be used as appropriate. The fiber diameter of the inorganic fiber is suitably 0.1 to 200 μm, and the fiber length is suitably 10 μm to 5 mm.
[0015]
Examples of other ceramic fibers include silica alumina fibers and silica fibers, and any of them may be those conventionally used as a holding material. Moreover, you may mix | blend a glass fiber, rock wool, and a biosoluble fiber.
[0016]
As the binder, an organic binder is generally used, and rubbers, a water-soluble organic polymer compound, a thermoplastic resin, a thermosetting resin, and the like can be used. Specifically, examples of the rubbers include a copolymer of n-butyl acrylate and acrylonitrile, a copolymer of ethyl acrylate and acrylonitrile, a copolymer of butadiene and acrylonitrile, and butadiene rubber. Examples of the water-soluble organic polymer compound include carboxymethyl cellulose and polyvinyl alcohol. Examples of the thermoplastic resin include acrylic acid, acrylic acid ester, acrylamide, acrylonitrile, methacrylic acid, homopolymers and copolymers such as methacrylic acid ester, acrylonitrile-styrene copolymer, acrylonitrile-butadiene-styrene copolymer Etc. Examples of the thermosetting resin include a bisphenol epoxy resin and a novolak epoxy resin.
[0017]
The vermiculite used in the present invention is, for example, a commercially available, untreated vermiculite that has been calcined to shrink by 1 to 4% by volume, preferably 3 to 4% by volume. The firing temperature is not limited as long as the temperature is 500 ° C. or lower, which is a foaming temperature. However, if the temperature is too high, the dehydration proceeds rapidly, which is not preferable. is there.
[0018]
More preferably, the calcined vermiculite is chemically treated with ammonium phosphate so that it can be foamed at a low temperature. As a treatment method, for example, calcined vermiculite may be charged into an aluminum phosphate solution, stirred for a predetermined time while heating, and then taken out and dried.
[0019]
The compounding ratio of the inorganic fiber, the binder and the calcined vermiculite in the holding material may be the same as that of the conventional intumescent mat holding material, and the inorganic fiber is 20 to 70% by mass, preferably 30 to 50% by mass, and the binder is 5 to 20% by mass. %, Preferably 8 to 15% by mass, and calcined vermiculite to 20 to 50% by mass, preferably 30 to 45% by mass.
[0020]
In order to obtain the holding material of the present invention, it may be the same as the conventional expansion type mat holding material, for example, an aqueous slurry in which inorganic fibers, a binder, and calcined vermiculite are mixed in the above ratio, and dewatered by a papermaking machine. After drying, it may be dried.
[0021]
The thickness of the holding material can be appropriately set according to the size of the applied catalytic converter, the operating temperature, and the like.
[0022]
As shown in FIG. 1, the holding material formed as described above is wound around the catalyst carrier 1 and interposed in the gap with the casing 2 in the same manner as in the related art. Then, after coming into contact with the exhaust pipe of the engine, the engine is operated to flow the exhaust gas, so that the calcined vermiculite foams due to the heat of the exhaust gas, a predetermined surface pressure is applied to the holding material, and the catalyst carrier Hold 1 In the holding material of the present invention, since the fired vermiculite is contracted in advance, the amount of contraction is small even when newly heated by the exhaust gas, and the decrease in surface pressure is also suppressed, so that the above holding state is favorably maintained. You. In addition, foaming at a lower temperature becomes possible by performing the ammonium phosphate treatment on the fired vermiculite.
[0023]
【Example】
Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited thereto.
[0024]
(Example 1)
[Firing vermiculite]
Vermiculite No. 1 was heated from room temperature at a temperature increasing rate of 100 ° C./hour, and when the temperature reached 360 ° C., the temperature was maintained at that temperature for 28 hours for dehydration and shrinkage. Next, the temperature was returned to room temperature at a temperature decreasing speed of 50 ° C./hour. By this baking treatment, the mass of vermiculite shrunk by 3.5% by volume as compared to before the treatment.
[0025]
[Chemical treatment of calcined vermiculite]
The vermiculite obtained by the above calcination treatment was put into a 30% by weight aqueous solution of ammonium phosphate, stirred sufficiently at 25 ° C., taken out and dried.
[0026]
(Preparation and evaluation of holding material)
45% by weight of silica-alumina fiber having a silica component and an alumina component of 50% by weight respectively, 13% by weight of an organic binder (acrylic emulsion: manufactured by Zeon Corporation), 42% by weight of the calcined and chemically treated vermiculite % Of the resulting mixture was dispersed in water to prepare an aqueous slurry. Then, this aqueous slurry was subjected to dehydration molding by a papermaking machine to form a mat-like holding material having a thickness of 5 mm.
[0027]
After the obtained holding material was held at a thickness of 4.5 mm for 30 minutes using a universal testing machine, the surface pressure was measured at room temperature and 350 ° C., respectively. % Had dropped.
[0028]
(Comparative Example 1)
A holding material was produced in the same manner as in Example 1 except that vermiculite No. 1 was not subjected to a baking treatment and was not subjected to a chemical treatment with ammonium phosphate. Then, the measurement of the rate of decrease in surface pressure was attempted in the same manner, but at 350 ° C., the vermiculite did not foam, and the measurement could not be performed.
[0029]
(Comparative Example 2)
A holding material was produced in the same manner as in Example 1, except that vermiculite No. 1 was not subjected to the baking treatment but was subjected to a chemical treatment with ammonium phosphate. Then, when the surface pressure was measured at normal temperature and 350 ° C., the surface pressure at 350 ° C. was greatly reduced by 60% as compared with the normal temperature.
[0030]
【The invention's effect】
As described above, the holding material of the present invention can reduce the foaming temperature, suppress the decrease in surface pressure due to heating while holding the catalyst carrier, and stably maintain the holding performance and the sealing performance of the catalyst carrier. .
[Brief description of the drawings]
FIG. 1 is a perspective view showing a holding material of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Catalyst support 2 Casing 3 Holding material

Claims (3)

A catalyst carrier, a casing containing the catalyst carrier, and a holding material used for a catalytic converter including a holding material wound around the catalyst carrier and interposed in a gap between the catalyst carrier and the casing, the inorganic material comprising: A holding material for a catalytic converter, comprising a fiber, a binder, and calcined vermiculite which has been shrunk in advance by calcining. The holding material for a catalytic converter according to claim 1, wherein the shrinkage ratio of the calcined vermiculite is 1 to 4% by volume. The holding material for a catalytic converter according to claim 1 or 2, wherein the calcined permiculite is further treated with ammonium phosphate.

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