JP2007218221A - Monolith holding material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a monolith holding material suitable for a large catalytic converter requiring stronger holding power, in the monolith holding material interposed between a monolith of the catalytic converter and a metallic casing. <P>SOLUTION: This monolith holding material 1 is constituted by laminating a plurality of heat resistant mats 2 and 3 formed in a belt shape and arranging fitting parts 25 and 35 mutually fitted to both end parts in the longitudinal direction. The respective mats 2 and 3 are set in the length respectively windable without looseness and fitted with the fitting parts 25 and 35 when wound on a monolith in a laminated state. Thus, adhesion to a monolith outer peripheral surface is enhanced by preventing generation of wrinkles on the inner peripheral side, and separation of a raw material is prevented by reducing tensile stress to the mat on the outer peripheral side. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a monolith holding material, and in particular, is a monolith holding material interposed between a monolith of a catalytic converter and a metal casing, and has a large size that requires a stronger holding force. The present invention relates to a monolith holding material suitable for a catalytic converter.

As is well known, a catalytic converter is a device that removes harmful components such as carbon monoxide, hydrocarbons, and nitrogen oxides contained in exhaust gas of an internal combustion engine with a noble metal catalyst, and is a monolith that is a catalyst carrier for exhaust gas purification. In order to protect the monolith from vibration, a monolith holding material made of a heat-resistant mat is interposed in the gap between the monolith and the metal casing. Such a monolith holding material is composed of, for example, a band-like alumina fiber mat that is compressed in the thickness direction and contains an organic binder. And it is wound around the outer peripheral surface of the monolith and accommodated in the casing together with the monolith, whereby the restoring force is developed after the organic binder disappears by thermal decomposition, and the monolith is elastically supported in the casing.
JP-A-8-61054 Japanese Patent Laid-Open No. 10-288032

  By the way, the catalytic converter used in a large internal combustion engine with a large displacement is larger in monolith itself and larger in mass than the one used in a small internal combustion engine. And durability is required. Therefore, the monolith holding material is designed to be thicker in order to increase the surface specific gravity. For example, in a catalytic converter mounted on a gasoline engine vehicle having a small displacement, the thickness of the monolith holding material is about 5 to 10 mm, whereas a catalytic converter mounted on a diesel engine vehicle having a large displacement and / or Alternatively, in the diesel particle filter (DPE), the thickness of the monolith holding material is about 10 to 30 mm.

  However, when the monolith holding material as described above is wound around the monolith, the difference in length between the inner periphery and the outer periphery increases depending on the thickness, so that wrinkles occur on the inner periphery side, and the outer periphery side is Pulled strongly in the circumferential direction. As a result, a gap is formed between the monolith and the monolith holding material, the inner portion and the outer portion are separated at the middle portion of the thickness of the monolith holding material, or a large gap is formed at the abutting portions at both ends in the length direction. It occurs. Due to these problems, there are concerns about a decrease in holding power and durability, and leakage of exhaust gas.

  The present invention has been made in view of the above circumstances, and an object thereof is a monolith holding material interposed between a monolith of a catalytic converter and a metal casing, and has a stronger holding force and durability. An object of the present invention is to provide a monolith holding material suitable for a large-sized catalytic converter that requires high performance.

  In order to solve the above problems, the monolith holding material of the present invention employs a structure in which a plurality of belt-shaped heat-resistant mats are laminated, and the length of each mat is the winding length of each of the monolith outer peripheral portions. Thus, the thickness of each mat is reduced, and the difference in length between the inner and outer circumferences of each mat when wound around a monolith is reduced.

  That is, the gist of the present invention is a monolith holding material interposed between a monolith that is an exhaust gas purifying catalyst carrier and a metal casing in a catalytic converter, and is formed in a belt shape and in the length direction thereof. It is constructed by stacking multiple heat-resistant mats with mating parts fitted to each other at both ends, and each mat can be wound without slack when wound around a monolith in a laminated state, and the mating parts are It exists in the monolith holding material characterized by being set to the length to fit.

  According to the monolith holding material of the present invention, a plurality of heat-resistant mats are laminated and each mat is set to a specific length, and the thickness of each mat can be designed to be thin and wound around the monolith. Since the difference in length between the inner and outer circumferences of each mat can be reduced, the wrinkle on the inner circumference side can be prevented and the adhesion to the outer surface of the monolith can be improved. The stress can be reduced to prevent the material from being peeled off, and both ends of each mat can be closely abutted with each other at the fitting portion. Therefore, even in a large-sized catalytic converter, sufficient holding power and durability can be exhibited, and leakage of exhaust gas can be prevented.

  An embodiment of a monolith holding material according to the present invention will be described with reference to the drawings. FIG. 1 is a perspective view showing a partially broken example of the outer shape and structure of a monolith holding material according to the present invention. FIG. 2 is a perspective view showing the structure of a catalytic converter to which the monolith holding material of the present invention is applied. In addition, the following description is a typical example of embodiment of this invention, and this invention is not limited to these content.

  The monolith holding material of the present invention (hereinafter abbreviated as “holding material”) vibrates the monolith (7), which is an exhaust gas purification catalyst carrier, in a catalytic converter, as indicated by reference numeral (1) in FIG. In order to protect it from, it is interposed between the monolith (7) and the metal casing (8).

  An example of the structure of the catalytic converter will be described. As shown in FIG. 2, the catalytic converter includes a monolith (7) that is formed in a cylindrical shape and carries an exhaust gas purifying catalyst, and a monolith (7). And a metal casing (8) connected to the exhaust pipe, and the holding material (1) wound around the monolith (7) and interposed in the gap between the monolith and the casing (8). Configured.

  As the monolith (7), a monolith made of a metal foil material can be used in addition to a monolith made of a ceramic mainly composed of cordierite or the like. In particular, ferritic stainless steel foils containing Fe, Cr, Al or Si as basic components are well-familiar with the coating material and catalyst when supporting the catalyst, and the thermal change after supporting the catalyst is relatively small. It is a material suitable for constituting a metal monolith. The monolith (7) usually has a function as a catalyst by supporting a noble metal layer such as Pt or Ph.

  The casing (8) has, for example, a two-part clamshell structure, and this structure is composed of a casing member (8a) constituting the upper half of the casing (8) and a casing member (8b) constituting the lower half. Two members are combined and integrated. The casing members (8a) and (8b) have flange portions (81a) and (81b), respectively, and the flange portions (81a) and (81b) are used when the casing members (8a) and (8b) are welded. It functions as a joint surface. Further, connection ports (91) and (92) for connection to the exhaust pipe are provided at both ends of one casing member (8b). In FIG. 2, reference numerals (82a) and (82b) denote bolt holes for fixing to the body of an automobile. As the metal casing, it is also possible to adopt a stuffing structure casing which is formed in a cylindrical shape in advance and into which a monolith is inserted from an opening at one end thereof.

  As shown in FIG. 1, the holding material (1) of the present invention is formed by laminating a plurality of heat-resistant mats (2), (3). The holding material (1) illustrated in the figure is configured by laminating two mats (2) and (3). Furthermore, mating portions (25) and (35) are provided at both ends of the mats (2) and (3) in the length direction so as to be mated with each other. The mats (2) and (3) are composed of an alumina fiber mat mainly composed of a laminate of alumina fibers. The alumina fiber mat refers to a sheet-like material mat before the outer shape is formed into mats (2) and (3). Further, the number of mats laminated is not particularly limited, but is usually 10 or less.

The fiber length of the alumina fiber is usually 20 to 200 mm, and the fiber diameter is usually 1 to 40 μm, preferably 2 to 20 μm. The alumina fibers preferably have a mullite composition of Al ₂ O ₃ / SiO ₂ weight ratio (hereinafter referred to as Al ₂ O ₃ / SiO ₂ ) = 70/30 to 74/26. Alumina fibers having Al ₂ O ₃ / SiO ₂ outside the above range are not suitable for long-term use because of rapid deterioration of the fibers due to crystallization and crystal growth at high temperatures.

  It is preferable that the crystallinity of said mullite composition alumina fiber is 0 to 10%. The crystallinity refers to the 2θ = 2θ of mullite-composed alumina fiber with respect to the peak intensity expressed at 2θ = 26.3 ° in X-ray diffraction of mullite that has been completely crystallized by baking at 1300 ° C. for 4 hours. The peak intensity at 26.3 ° is expressed as a percentage (%). Since the low crystalline mullite composition alumina fiber has few crystals as the core of crystal growth, the fiber hardly deteriorates even when heated at 800 to 1000 ° C.

  In addition, a shot having a large particle diameter of 45 μm or more tends to cause fiber cutting and impair the recoverability of the mats (2) and (3). Furthermore, a shot with a large particle size partially increases the specific gravity of the mats (2) and (3), which causes non-uniform thermal conductivity. When used as a holding material (1), There is a risk that uniform holding may be difficult. Therefore, it is preferable that the alumina fiber applied to the present invention has a content of shots having a particle diameter of 45 μm or more of 7% by weight or less.

The single fiber tensile strength of the alumina fiber is preferably 150 to 400 kg / mm ² . If the tensile strength is less than 150 kg / mm ² , sufficient surface pressure cannot be obtained when used as the heat-resistant holding material (1). On the other hand, when the tensile strength exceeds 400 kg / mm ² , the fiber tends to become brittle.

  The above-mentioned alumina fiber is superior in heat resistance and has very little thermal deterioration such as softening shrinkage compared to other ceramic fibers, and therefore has high elasticity when formed into mats (2) and (3). That is, a high holding force is generated with a low bulk density and the temperature change is small. Therefore, when used as a holding material (1) for a catalytic converter, the monolith (7) is also used when the gap between the monolith (7) and the casing (8) changes due to the difference in thermal expansion and the bulk density thereof increases. This is superior in that the holding pressure against the pressure does not change rapidly.

  The alumina fiber mat constituting the mats (2) and (3) uses, for example, a spinning stock solution comprising a mixture of an alumina source such as aluminum oxychloride, a silica source such as silica sol, an organic binder such as polyvinyl alcohol, and water. Is obtained as follows. That is, the spun alumina fiber precursor is laminated to form a sheet, and then preferably subjected to needle punching, and then usually fired at 1000 to 1300 ° C.

Said needle punching process has the effect of orienting a part of fiber to the vertical direction with respect to the lamination surface. Therefore, a part of the alumina fiber precursor in the sheet penetrates the sheet and is oriented in the longitudinal direction to bind the sheet, so that the bulk specific gravity of the sheet is increased, and delamination and delamination between layers are prevented. The The density of needle punching is usually 1 to 50 strokes / cm ² , and the thickness, bulk specific gravity, and strength of the alumina fiber mat are adjusted by the density of needle punching.

  When the monolith (7) is accommodated in the casing (8) in the catalytic converter, the holding material (1) (mat (2)) is formed against the gap formed by the outer peripheral surface of the monolith (7) and the inner surface of the casing (8). And the laminated body (3) need not have the same thickness, and can be mounted up to a slightly thicker one. However, when it is too thick or when sliding with the casing (8) is bad, a part of the fibers of the mats (2) and (3) protrudes from the joint surfaces of the flange portions (81a) and (81b) and is welded. Cause inconvenience such as impossible. Therefore, the entire thickness of the holding material (1) (the total thickness of the mat (2) and the mat (3)) is usually set to 1.0 to 2.0 times the gap. The upper limit of such a set value is preferably 1.7 times, more preferably 1.6. Incidentally, the thickness of the holding material (1) applied to a large-sized catalytic converter is about 10 to 30 mm.

  On the other hand, when the mats (2) and (3) are wound around the monolith (7) as the holding material (1), wrinkles are generated on the inner peripheral surfaces of these mats as little as possible. It is desirable that tensile stress does not act as much as possible. Accordingly, in the present invention, the thickness of each mat (2), (3) is usually 3 by taking into consideration the total thickness required for the holding material (1) and adjusting the number of laminated mats. It is set to ˜15 mm, preferably 5 to 10 mm.

  In the present invention, when an alumina fiber mat is formed, other ceramic fibers and inorganic expansion materials may be used in combination with the alumina fibers. In this case, it may be uniformly mixed with the alumina fiber mat. However, it is possible to reduce the cost while maintaining the performance of the auxiliary material by localizing the material while avoiding the heated portion. Examples of the ceramic fiber include silica fiber, glass fiber, and asbestos fiber, and examples of the inorganic expanding material include bentonite, expandable vermiculite, and expandable graphite.

  The production method of the alumina fiber mat is basically the same as the known method described in Japanese Patent No. 3025433, etc. The first step of impregnating the made alumina fiber mat with the organic binder liquid, the organic binder It consists of a second step of compressing the alumina fiber mat impregnated with the liquid in the thickness direction, and a third step of removing the medium liquid of the organic binder liquid while maintaining the thickness of the compressed alumina fiber mat.

  As the organic binder, a water-soluble organic polymer compound, a thermoplastic resin, a thermosetting resin, or the like is used. Examples of the water-soluble organic polymer compound include carboxymethyl cellulose and polyvinyl alcohol. As the thermoplastic resin, acrylic resins such as acrylic acid, acrylic acid ester, acrylamide, acrylonitrile, methacrylic acid, methacrylic acid ester homopolymer, acrylonitrile / styrene copolymer, acrylonitrile / butadiene / styrene copolymer, etc. Examples include various types of copolymers. Examples of the thermosetting resin include bisphenol type epoxy resins and novolac type epoxy resins.

  Among the above organic binders, acrylic resins that are acrylic or methacrylic polymers are preferred. In particular, an organic binder having a glass transition point (Tg) of −22 to 100 ° C., preferably −22 to 70 ° C., more preferably −22 to 40 ° C. is preferable. When the Tg of the organic binder is less than −22 ° C., the attachment work is difficult because the binder adheres to the apparatus in the production process of the alumina fiber mat and the surfaces of the produced mats (2) and (3) are sticky. Further, when the Tg of the binder exceeds 100 ° C., the flexibility of the resulting mats (2) and (3) is lowered and the handling property is lacking. The Tg of the homopolymer can be measured according to a known method, and the Tg of the copolymer can be determined from the Gordon-Taylor formula by the Tg of each copolymer monomer and the composition of each copolymer monomer. The ratio can be obtained by arithmetic averaging.

  The organic binder is used as an aqueous solution, a water-dispersed emulsion, a latex, or an organic solvent solution (collectively referred to as “binder liquid”). As the binder liquid, a commercially available product can be used as it is or diluted with water or the like. In addition, the organic binder does not necessarily need to be 1 type, and even if it is a mixture of 2 or more types, there is no problem. Among the above organic binders, water-soluble polymer compounds such as carboxymethyl cellulose and polyvinyl alcohol or acrylic resins are preferable. An acrylic or methacrylic polymer is particularly preferable.

  In the first step of manufacturing the alumina fiber mat, the alumina fiber mat is impregnated with the organic binder liquid by, for example, a method of immersing the mat in an organic binder liquid or a method of spraying the organic binder liquid on the mat. The content of the organic binder (value as an active ingredient) is usually 1 to 30 parts by weight, preferably 3 to 20 parts by weight with respect to 100 parts by weight of the alumina fiber. If the content of the organic binder is less than 1 part by weight, the thickness of the molded body may not be maintained due to the repulsive force of the mat, and if it exceeds 30 parts by weight, the cost is increased and the molded body is flexible. There is a possibility that the property is impaired.

  In the second step, the alumina fiber mat impregnated with the organic binder liquid is compressed in the thickness direction by a compression means such as a press plate or a press roller. As the press plate, two liquid-permeable plate-like bodies, Typically, a punching metal, a resin net, a metal net (mesh), a perforated plate or a plate with good air permeability can be used, etc. It is preferable to use a suction means for the binder liquid as the compression means. In the third step, which is performed following the second step, the thickness of the alumina fiber mat (compressed mat) is maintained by high-temperature hot air treatment under a temperature condition in which the organic binder does not change or decompose. The medium liquid of the organic binder liquid is removed, whereby a sheet-like heat-resistant alumina fiber mat is obtained.

  The above-mentioned alumina fiber mat is cut using a punching molding machine provided with a cutting blade having a fixed shape corresponding to the planar shape of the mats (2) and (3), as shown in FIG. Molded as mats (2) and (3). The planar shapes of the mats (2) and (3) are formed in the shape of elongated strips as shown in the figure, and the mats (2) and (3) are respectively provided at both ends in the length direction. In the mat, fitting portions (25) and (35) for fitting each other are provided.

  The length of each mat (2), (3) is set to a length that allows the mats (25), (35) to be fitted to each other when they are wound around a monolith in a laminated state without loosening. Is done. Specifically, when the holding material (1) has a two-layer structure, as shown in FIGS. 1 and 2, the mat (3) is a mat that is wound directly on the outer peripheral surface of the monolith (7). The length of the mat (3) (the length not including the protruding length of the convex portion (35b) of the fitting portion (35) described later) is substantially the same as the outer peripheral length of the monolith (7). On the other hand, the mat (2) is a mat arranged on the outer periphery of the mat (3), and includes the length of the mat (2) (including the protruding length of the convex portion (25b) of the fitting portion (25) described later). Is not substantially the same as the outer peripheral length of the mat (3) wound around the monolith (7). The widths of the mats (2) and (3) are set to be slightly shorter than the length of the monolith (7) (the length along the center line).

  The mating portions (25) and (35) at both ends of the mats (2) and (3) are shifted from the ends of the mats (2) and (3) during the winding work around the monolith (7). A structure in which a minute gap (joint) generated when both ends are abutted is bent when viewed in plan (when viewed from a direction perpendicular to the outer peripheral surface in a state wound around the monolith (7)) It is provided to become.

  Specifically, when each of the mats (2) and (3) is viewed in plan view, one of the fitting portions (25) and (35) (the left portion in FIG. 1) is formed as a recess (25a) and (35a), respectively. The other fitting portions (25) and (35) (right side portion in FIG. 1) are formed as convex portions (25b) and (35b). As described above, the mating portions (25) and (35) having a structure bent when they are abutted (for example, an uneven structure as shown in the figure) are provided on the mats (2) and (3), so that the holding material (1 ), It is possible to prevent leakage of exhaust gas from the mating portions of the mats (2) and (3).

  Furthermore, in the holding material (1) of the present invention, in order to prevent leakage of exhaust gas from the mating portions of the mats (2) and (3) more reliably, the mats (2) and (3) As shown in FIG. 2, when wound around the monolith (7) in a laminated state, the length of each fitting portion (25), (35) is shifted as shown in FIG. It is laminated in a state shifted in the direction.

  That is, as shown in FIG. 1, the mat (2) and the mat (3) are formed so that the respective concave portions (25a) and the concave portions (35a) do not overlap with each other, and the respective convex portions (25b) and convex portions (35b) are formed. They are stacked so that they do not overlap. Thereby, the minute gap (joint) formed by abutting both ends of the mat (2) and the minute gap (joint) formed by abutting both ends of the mat (3) can be shifted. Can prevent the leakage path for the exhaust gas from forming in cooperation between the monolith (7) and the casing (8).

  Further, in the holding material (1) of the present invention, in order to enhance the workability when assembling the catalytic converter and wind the mats (2) and (3) without loosening, the stacked mats, that is, FIG. It is preferable that the mats (2) and (3) illustrated in (1) are fixed to each other so that at least one end side is freely movable. More preferably, both ends of the mats (2) and (3) are fixed to each other so as to be freely movable except for a binding portion (4) (fixing portion) described later.

  Specifically, for example, the mat (2) and the mat (3) are fixed to each other by one bundling portion (4) by sewing. Such a binding portion (4) is provided so as to be continuous in the width direction of the mats (2) and (3). Thus, when the holding material (1) is wound around the monolith (7), the mutual movement in the width direction of the mat (2) and the mat (3) is restricted, and the mat (2 ) And both ends of the mat (3) can be moved in the length direction. As a result, when the holding material (1) is wound around the monolith (7), the holding material (1) can be handled integrally, and the mat (2) and the mat (3) can be independently provided. Can be wound without loosening. The binding portion (4) is the length of the mat from the vicinity of the end of the mat (3) on the convex portion (35b) side, specifically, from the edge of the mat (3) on the convex portion (35b) side. Is usually within a range of 1/2, preferably within 1/3. The means for fixing the mats (2) and (3) to each other may be an adhesive, a staple or the like.

  In the catalytic converter as shown in FIG. 2 described above, after holding the holding material (1) around the monolith (7), the monolith (7) around which the holding material (1) is wound is housed in the casing (8). Manufactured by. When the holding material (1) of the present invention is wound around the monolith (7), the mat (2), (3) has a width direction along the length direction (center line direction) of the monolith (7) and the mat. Wrap around the monolith (7) so that the length direction of (2) and (3) is along the circumferential direction of the monolith (7).

  At that time, first, the mat (3) having a short length is wound around the monolith (7), and the concave portion (35a) and the convex portion (35b) which are the fitting portions (35) at both ends are fitted. Subsequently, the mat (2) having a long length is wound around the front side of the mat (3), and the concave portion (25a) and the convex portion (25b) which are the fitting portions (25) at both ends are fitted. And the fitting part (25) of the mat | matte (2) located outside is fixed with an adhesive tape or the like.

  The holding material (1) of the present invention has a structure in which, for example, two mats (2) and (3) in a strip shape are laminated as described above, and the length of each mat (2) and (3). However, the mats (2) and (3) should be reduced in thickness because each of the mating parts (25) can be wound around the monolith (7) without any looseness. And the difference between the lengths of the inner and outer circumferences of the mats (2) and (3) when wound around the monolith (7) can be reduced.

  Therefore, in the holding material (1) of the present invention, when wound around the monolith (7) as described above, it is possible to prevent the occurrence of wrinkles on the inner peripheral side (the inner peripheral portion of the inner mat (3)), The adhesion to the outer peripheral surface of the monolith (7) can be increased. Moreover, the tensile stress in the outer peripheral side (the outer peripheral portion of the outer mat (2)) can be reduced, and peeling of the alumina fiber mat that is the material can be prevented. And in each mat | matte (2) and (3), the fitting parts (25) and (35) of both ends can be faced | matched closely, respectively. Therefore, according to the holding material (1) of the present invention, sufficient holding power and durability can be exhibited even in a large-sized catalytic converter, and leakage of exhaust gas can be reliably prevented.

  Furthermore, the holding material (1) of the present invention is formed by laminating the thin mats (2) and (3) as described above, and is manufactured as a holding material for a small catalytic converter. Since a thin alumina fiber mat can be used as it is simply by changing the width and length, it can be manufactured at a lower cost.

  Further, the holding material (1) of the present invention is formed in the mating portions (25) and (35) because the mats (2) and (3) are laminated in a state shifted in the length direction. A minute gap (joint) can be shifted, and leakage of exhaust gas can be prevented more reliably. Further, since these mats are fixed to each other so that at least one end side of each mat (2), (3) can be freely moved, they can be handled integrally, and the mat (2) and the mat (3 ) Can be wound without loosening. And since the mats (2, (3)) are composed of a low crystalline alumina fiber mat having a mullite composition, there is no high-temperature heat deterioration and no fiber breakage, so that the holding power against the monolith (7) is reduced. And the monolith (7) can be fixed more stably.

It is a perspective view which shows an example of the external appearance and structure of the monolith holding material which concerns on this invention partially fractured | ruptured. It is a perspective view which shows the structure of the catalytic converter to which the monolith holding material of this invention is applied.

Explanation of symbols

1: monolith holding material 2: mat 25: fitting portion 25a: concave portion 25b: convex portion 3: mat 35: fitting portion 35a: concave portion 35b: convex portion 4: binding portion 7: monolith 8: casing

Claims (4)

  A monolith holding material interposed between a monolith that is a catalyst carrier for exhaust gas purification and a metal casing in a catalytic converter, and is formed in a strip shape and mated with each other at both ends in the length direction Each mat is set to a length that allows each mat to be wound without loosening and fitted into the mating portion when wound around a monolith in a stacked state. A monolith holding material characterized by having   2. The monolith holding material according to claim 1, wherein each mat is laminated in a state shifted in the length direction so that each mating portion is shifted when wound around the monolith in a stacked state.   The monolith holding material according to claim 1 or 2, wherein the mats are fixed to each other so that at least one end side thereof is freely movable.   The monolith holding material according to any one of claims 1 to 3, wherein the mat comprises a low-crystalline alumina fiber mat having a mullite composition.

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