WO2001083956A1

WO2001083956A1 - Thermal insulating material and pollution control device

Info

Publication number: WO2001083956A1
Application number: PCT/US2001/013182
Authority: WO
Inventors: Takuma Aizawa; Takayuki Kawai; Toshihiro Kasai; Toshiyuki Watanabe
Original assignee: 3M Innovative Properties Company
Priority date: 2000-04-28
Filing date: 2001-04-24
Publication date: 2001-11-08
Also published as: AU2001253787A1

Abstract

Thermal insulating material which is efficiently produced while the content of organic matters such as organic fibers and/or an organic binder is reduced to the same or higher degree as compared with a conventional catalytic converter, and which is applied to a catalyst converter while an unpleasant feeling to the operator is avoided as possible. A thermal insulating material comprising a thermal insulating material body formed of a bulk material of inorganic fibers, and a coating provided on at least one surface of said thermal insulating material body. The thermal insulating material can be useful in mounting the pollution control element of a pollution control device.

Description

Thermal Insulating Material and Pollution Control Device

Field of the Invention

The present invention relates to thermal insulating materials, particularly to thermal insulating materials useful in a pollution control device and, more particularly, to a pollution control device wherein a pollution control element is mounted in a casing using the thermal insulating material.

Background of the Invention Pollution control devices such as, for example, catalytic converters and exhaust emissions filters (e.g., diesel exhaust filters) are well known for use in the exhaust systems of internal combustion engines. One such system is an exhaust gas purifying system using a ceramic catalytic converter to purify an exhaust gas containing carbon monoxide (CO) and hydrocarbon (HC) exhausted from the engine of automobiles. A ceramic catalytic converter typically contains a honeycomb catalyst support (catalyst element) made of ceramic in a casing that is usually a housing made of metal.

Thermal insulating materials have been used to mount the pollution control element of a number of pollution control devices. For example, generally, the space between a catalyst support and a casing, which are contained in a ceramic catalytic converter, is filled with a thermal insulating material consisting typically of inorganic fibers and organic fibers and/or a liquid or pasty organic binder as disclosed in Japanese Unexamined Patent Publication (Kokai) No. 57-61686, 59-10345 or 61-239100. As a result, the thermal insulating material, with which the space is filled, retains the catalyst support, thereby making it possible to prevent a mechanical shock caused by impact and vibration, or a thermal shock caused by heat cycles from giving to the catalyst support.

According to a catalytic converter with such a constitution, a desired operation can be realized because breakage or movement of the catalyst support does not occur.

The above-described exhaust gas purifying system is generally provided with an oxygen sensor and it controls the concentration of oxygen in the exhaust gas, thereby to effect optimum purification of the exhaust gas through a catalytic converter. It is considered to be preferred that the catalytic converter is operated at a higher temperature so as to improve purification of the exhaust gas and to improve the fuel cost. With the recent tightening of exhaust gas control due to protection of the global environment, further purification of the exhaust gas due to an increase in operating temperature tends to be effected. On the other hand, a nitrogen oxide (No_x) tends to be easily evolved in the exhaust gas as a result of an increase in operating temperature. Accordingly, it has been known that an air fuel ratio due to an accurate signal from an oxygen sensor is important in the exhaust gas purifying system.

However, the thermal insulating material as disclosed in the above publications (Kokai) can not be easily used, together with a high sensitivity oxygen sensor. The reason is as follows. That is, since an organic matter such as organic fibers and/or organic binder are added in the above thermal insulating material in a comparatively large amount, i.e. about 4 to 50% wt%, based on the total amount of the thermal insulating material, the organic matter is likely to be easily incorporated into the exhaust gas on initial operation of the catalytic converter, thereby to cause wrong operation of the exhaust gas purification system. On the other hand, Japanese Unexamined Patent Publication (Kokai) No. 11-

166414 discloses a thermal insulating material comprising crystalline alumina fibers as a principal component, wherein the content of an organic matter is reduced to 1 wt% or less. However, since the surface of this thermal insulating material is covered with a protective sheet, an additional complicated step of removing the protective sheet must be carried out after the thermal insulating material was disposed between a casing and a catalyst support so as to apply it to a catalytic converter. There is also a problem about disposal of the removed protective sheet.

Japanese Unexamined Patent Publication (Kokai) No. 6-239656 discloses a multilayer structure thermal insulating material. This publication teaches to produce the multi- layer structure thermal insulating material by using a very small amount of a polymer aggregating agent of an organic matter. However, a complicated step of laminating a plurality of mats must be required because of a multi-layer structure of the thermal insulating material.

Japanese Unexamined Patent Publication (Kokai) No. 7-286514 discloses a holding seal material (corresponding to a thermal insulating material) made by treating a laminated material of inorganic fibers such as crystalline alumina fibers using a needle punching method. The holding seal material is likely to cause protrusion or scattering of inorganic fibers from the surface of the insulating material, although the organic matter is removed by calcining the laminated material. As a result, the end portion of the inorganic fibers tends to be directly contacted with the operator to impart an unpleasant feeling to him on incorporation of the above holding seal material into the catalyst converter.

Summary of the Invention

As described above, various thermal insulating materials have hitherto been suggested to apply to pollution control devices (e.g., a catalytic converter), however, still some room for improvement is left in any of thermal insulating materials. It can be an object of the present invention to provide a thermal insulating material which is efficiently produced while the content of organic matters such as organic fibers and/or an organic binder is reduced to the same or higher degree as compared with a conventional catalytic converter.

It can be an additional object of the present invention to provide a thermal insulating material that can be applied to a catalyst converter, or other pollution control device, while an unpleasant feeling to the operator is avoided as possible.

It can be another object of the present invention to provide a catalytic converter, or other pollution control device, using such an excellent thermal insulating material.

According to the present invention, the above-described problems can be solved by providing a thermal insulating material comprising a thermal insulating material body formed of a bulk material of inorganic fibers, and a coating provided on at least one surface of said thermal insulating material body.

According to the present invention, there is also provided a pollution control device (e.g., a catalytic converter) that comprises a casing, a pollution control element (e.g., a catalyst element) disposed in the casing, and a thermal insulating material disposed between the casing and the catalyst element. The thermal insulating material comprises a thermal insulating material body formed of a bulk material of inorganic fibers, and a coating provided on at least one surface of the thermal insulating material body.

Brief Description of the Drawings

Fig. 1 is an exploded perspective view showing preferred one embodiment of the catalytic converter according to the present invention. Fig. 2 is a SEM photograph showing the surface of the thermal insulating material made in Example 1.

Fig. 3 is a SEM photograph showing the surface of the thermal insulating material made in Example 2. Fig. 4 is a SEM photograph showing of the surface of the thermal insulating material made in Example 3.

Fig. 5 is a SEM photograph showing the surface of the thermal insulating material made in Comparative Example 1.

Fig. 6 is a SEM photograph showing the surface of the thermal insulating material made in Example 4.

Fig. 7 is a SEM photograph showing the surface of the thermal insulating material made in Comparative Example 2.

Fig. 8 is a SEM photograph showing the surface of the thermal insulating material made in Comparative Example 3. Fig. 9 is a SEM photograph showing the surface of the thermal insulating material made in Example 5.

Detailed Description of the Invention

The present invention is further illustrated in accordance with the following embodiments. It is apparent to a person with an ordinary skill in the art that the present invention is not limited to the following embodiments, and various changes and modifications can be made in the invention without departing from the scope thereof.

Fig. 1 is a perspective view showing typical one embodiment of a catalytic converter according to the present invention, wherein an exploded state of the catalytic converter is illustrated for easier understanding of its constitution. A catalytic converter

10 shown in the drawing is provided with a metal casing 11, a monolithic solid catalyst element 20 disposed in the metal casing 11, and a thermal insulating material disposed between the metal casing 11 and the catalyst element 20. As described above and will be described in detail hereinafter, according to the present invention, the thermal insulating material comprises a thermal insulating material body 30 (for convenience, this body is also referred to as "thermal insulating material) formed from a bulk material of inorganic fibers and a coating 31 applied onto a surface thereof. The thermal insulating material body 30 further comprises an integrated component of the inorganic fibers, and an organic matter is contained in the integrated component of the inorganic fibers in the amount of 3 wt% or less based on the total amount of the thermal insulating material body, coating and integrated component. The catalytic converter 10 is provided with an exhaust gas inlet 12 and an exhaust gas outlet 13, each of which has a shape of truncated cone.

The solid catalyst element in the metal casing is made of a honeycomb structure catalyst support made of ceramic, which has a plurality of exhaust gas passages (not shown). The thermal insulating material of the present invention is disposed around the catalyst element. The thermal insulating material retains the catalyst element in the metal casing and seal the space formed between the catalyst element and the metal casing, thereby making it possible to prevent the exhaust gas from flowing with by-passing the catalyst element or to minimize such undesired flow. The catalyst element is retained in the metal casing firmly and elastically.

In the catalytic converter of the present invention, the metal casing can be made of various metallic materials known in this field in any shape according to the operation and effect. Preferred metal casing is made of stainless steel and has a shape as shown in Fig. 1. As a matter of course, the metal casing can be optionally made of metal such as aluminum, titanium, etc. or an alloy thereof in any suitable shape.

Similarly to the metal casing, the solid catalyst support can also be made of the same material as that employed in a conventional catalytic converter in the same shape.

Proper catalyst element includes those which are well known to a person with an ordinary skill in the art and are produced from metal or ceramic. Useful catalyst element is, for example, disclosed in Reissued U.S. Patent No. 27,747. The catalyst element made of ceramic is, for example, commercially available from Corning Inc. in U.S.A. For example, honeycomb catalyst supports made of ceramic are commercially available from

Corning Inc. under the trade name of "CELCOR" and are commercially available from NGK Insulated Ltd. under the trade name of "HONEYCERAM", respectively. The catalyst element made of metal is, for example, commercially available from Behr GmbH and Co. in Germany. See Document No. 900500 of SAE Technical Document, Stroom et al., "Systems Approach to Packaging Design for Automotive Catalytic Converters",

Document No. 800082 of SAE Technical Document, Howitt, "Thin Wall Ceramics as Monolithic Catalyst Support", and Document No. 740244 of SAE Technical Document, Howitt et al., "Flow Effect in Monolithic Honeycomb Automotive Catalytic Converter" with respect to the detailed description of the monolithic catalyst.

The catalyst to be supported on the above-described catalyst element is usually metal (e.g. platinum, ruthenium, osmium, rhodium, iridium, nickel, palladium, etc.) or metal oxide (e.g. vanadium pentaoxide, titanium dioxide, etc.) and is preferably used in the form of coating. See U.S. Patent No. 3,441,381 with respect to the detailed description of coating of such a catalyst.

In the practice of the present invention, it is particularly preferred that a casing made of metal is basically made by, for example, containing a honeycomb catalyst support (catalyst element) made of ceramic, and that a catalyst element is made, for example, by supporting a catalyst layer (catalyst coating) made of noble metal such as platinum, rhodium and palladium on a honeycomb monolithic carrier made of ceramic. With such a constitution, an effective catalytic action can be exhibited at a comparatively high temperature. According to the present invention, a thermal insulating material is disposed between the metal casing and the catalyst element contained therein. The thermal insulating material is preferably made of a single-layer thermal insulating material. Describing in detail, this thermal insulating material is basically comprises a thermally insulating material body formed from a bulk material of inorganic fibers and a coating. The inorganic fibers are, for example, made of alumina, silica, silicon nitride, rock wool, aluminosilicate, zirconia or the like, and can be employed to retain the catalyst element because of thermal insulation properties, heat resistance and elasticity. In case where the inorganic fibers are made of alumina, the inorganic fibers can maintain the heat resistance and elasticity even at a high temperature higher than 900°C. As these inorganic fibers made of alumina, several kinds of inorganic fibers are commercially available from

DYSON Co. under the trade name of "SAFFIL". Similar inorganic fibers made of alumina are commercially available from manufacturers such as DENKA, NITIAS, MITSUBISHI CHEMICAL INDUSTRIES Co. and the like.

According to the present invention, the thickness (average diameter) of the inorganic fibers is not limited, but the inorganic fibers preferably have the average diameter within a range from 2 to 4 μm. When the inorganic fibers have the average diameter of smaller than about 2 μm, the resulting thermal insulating material tends to be brittle and to lack in strength. On the other hand, when the inorganic fibers preferably have the average diameter larger than about 4 μm, it becomes difficult to form the thermal insulating material.

Similar to the thickness, the length of the inorganic fibers is not specifically limited. However, the inorganic fibers preferably have an average length within a range from 0.5 to 50 mm. When the average length of the inorganic fibers is smaller than about 0.5 mm, features of the fiber form may not be obtained. On the other hand, when the average length is larger than about 50 mm, it becomes difficult to enable the production process of the thermal insulating material to proceed smoothly. In addition to the bulk material of the inorganic component, an integrated component of the inorganic component is further contained in the thermal insulating material of the present invention. This integrated component has a function of retaining the inorganic fibers, and accelerating aggregation of the inorganic fibers sometimes. According to the present invention, this integrated component can be composed of a binding medium made of crimped organic fibers (organic matter), namely, a binder.

Describing in detail, these crimped organic fibers are preferably composed of a heat- resistant core and a sheath-core structure wherein the core is covered with a fused clad.

The fused clad of the organic fibers having the above-described sheath-core structure is softened at a comparative low temperature within a range from 110 to 220°C, thereby making it possible to adhere and bond the organic fibers each other or the inorganic fibers with the organic fibers. The heat-resistant core is crimped and retains the shape even at a comparatively high temperature within a range from 200 to 250°C, thereby making it possible to physically interlock the inorganic fibers.

Thus, a liquid or pasty organic binder, which has been required essentially to use so as to impart a mechanical strength to the thermal insulating material in the prior art, is not required in the practice of the present invention. Accordingly, the crimped organic fibers as the binder to be used in the present invention themselves can firmly retain the inorganic fibers by not only adhesion but also a physical interlock. Particularly, it has been found that the comparable mechanical strength to that in the prior art can be imparted to the thermal insulating material even if the content of the binder is reduced to about 3 wt% or less so as to avoid a wrong operation of the exhaust gas purification system as possible. Typical fused clad in the constitution of the crimped organic fibers is, for example, made of modified polyethylene terephthalate (PET), polyethylene (PE), polypropylene, polyester, nylon, polybutylene terephthalate or the like. The modified PET is particularly preferred because it is fused by heating (120 to 140°C) in the drying step on forming of the thermal insulating material.

The typical heat-resistant core in the constitution of the crimped organic fibers is composed of PET, PE, polypropylene, polyester, nylon, polybutylene terephthalate or the like. PET is particularly preferred in view of the heat resistance (250°C) to heating in the above-described drying process. The length of the crimped organic fibers used as the binder is not specifically limited, but the crimped organic fibers preferably have an average length of 1 to 20 mm. When the average length is smaller than about 1 mm, interlock between the organic fibers each other or that between the inorganic fiber and organic fibers is reduced, thereby making it impossible to make use of advantages derived from the shape of the crimped fibers. On the other hand, when the average length is larger than about 20 mm, winding on equipment during the process or interlock between the fibers becomes severe to cause drastic scatter in composition distribution or thickness, thereby making it difficult to make a good thermal insulating material. More preferably, the organic fibers have an average length within a range from 5 to 15 mm. The thickness (average diameter) of the crimped organic fibers is not specifically limited, but preferably the crimped organic fibers have an average diameter within a range from 1 to 4 deniers (about 0.11 to 0.44 g/km). When the average diameter of the organic fibers is smaller than about 1 denier, the amount of the fused clad on the surface of the organic fibers is reduced and the resulting strength tends to be smaller than the desired strength. On the other hand, when the average diameter of the organic fibers is smaller than about 4 deniers, the surface area based on the weight is reduced and, therefore, it becomes impossible to effect efficient fusion, resulting in poor strength.

An inorganic or organic aggregating agent may be contained in the integrated component in an amount smaller than that of the binder, thereby accelerating aggregation and integration of the inorganic fibers in the production of the thermal insulating material described hereinafter. For example, the inorganic aggregating agent includes, but is not specifically limited to, sepiolite, montmorillonite, bentonite, alumina sol, colloidal silica or the like. Particularly, as a result of utilization of surface charge, the organic aggregating agent (organic matter) can not only accelerate integration with the inorganic fibers to reduce the thickness of the thermal insulating material, but also reduce the amount of the binder of the organic fibers. That is, since the inorganic fibers have a negative charge, if the positively charged aggregating agent is added to the integrated component, the opposed inorganic fibers may be integrated through the aggregating agent. Also the organic aggregating agent is not specifically limited but includes, for example, amide polyacrylate, polyvinyl alcohol, acrylic polymer, urethane, vinyl acetate, rubber, latex or the like. Particularly, amide polyacrylate is commercially available as a diluted product from MITSUI S AJTEK Co. under the trade name of "AKURAK 135 " and "AKURAK

304E".

In the practice of the present invention, it is preferred to add those, which are generally used as a paper strength enhancer in the technical field of paper-making, in combination with the aggregating agents. The paper strength enhancer is an additive for improving the normal strength or wet strength of the paper and includes, for example, amide polyacrylate. The paper strength enhancer is effective to improve the dry strength of the thermal insulating material in the thermal insulating material of the present invention. Suitable paper strength enhancer is, for example, commercially available from HARIMA CHEMICALS Co., under the trade name of "HERMIDE B-15". However, the thermal insulating material body constituting the thermal insulating material is not limited to those described above, and an inorganic binding medium of glass fibers may be used as an integrated component of an inorganic component in place of organic fibers having the above-described sheath-core structure as far as requirements for thermal insulating material body are satisfied. Also in such a case, the wrong operation of the purification system can be further reduced or avoided. According to the present invention, the glass fibers can impart the fixed strength and durability to the thermal insulating material while maintaining the inorganic fibers when the space between the inorganic fibers is filled with the softened or molten glass fibers. The glass fibers are preferably made of a non-alkali glass in view of prevention of embrittlement caused by diffusion of an alkali element into the inorganic fibers, although the material is not specifically limited. Also the length is not specifically limited, but is usually within a range from about 1 to 25 mm, and preferably from about 8 to 12 mm. Alternatively, the thermal insulating material body may be those obtained by calcining, a laminated material of inorganic fibers such as crystalline alumina fibers, after treatment of the fibers using a needle punching method. Such a thermal insulating material body is commercially available from MITSUBISHI CHEMICALS Co., Ltd. under the trade name of "MAFTEC BLANKET" as a holing seal material for catalyst converter.

Furthermore, at least one, preferably both surfaces, of the above-described thermal insulating material body is/are coated. Protrusion or scattering of the inorganic fibers from the surface of the thermal insulating material body can be prevented by the coating without lowering the mechanical strength of the thermal insulating material. As a result, the thermal insulating material of the present invention can prevent the end portion to directly contact with the operator on incorporation of it into a catalyst converter, thereby making it possible to remove an unpleasant feeling to the operator.

The material of the coating is not limited as far as the content of organic matters in the thermal insulating material can be reduced as possible. The coating may be formed of an organic polymer compound, for example, rubber polymer such as acrylic polymer of polyacrylate, which is commercially available from NIPPON ZEON Co., Ltd. under the trade name of "LX-816", urethane polymer, or polyacrylonitrile-butadiene rubber (NBR), or polyvinyl alcohol. Preferably, the coating is formed of an inorganic compound, for example, an alkali silicate such as potassium silicate or sodium silicate, or a combination thereof, in view of reduction of the organic matters.

The above-described thermal insulating material can be produced according to various well-known and conventional procedures. For example, the thermal insulating material using as the integrated component organic fibers having the sheath-core structure may be produced in accordance with the following preferred method.

First, inorganic fibers and organic fibers (binder) are put in water, and these fibers are opened and mixed.

While stirring the inorganic fibers and organic fibers slowly, an inorganic or organic aggregating agent is added to prepare a slurry. Thereafter, a sheet is formed by paper-making of the resulting slurry. The resulting formed article is squeezed to previously remove excess water. Subsequently, the formed article is heated and dried at a predetermined temperature with pressing, thereby to molten the fused clad on the surface of the organic fibers and to adhere and bond the organic fibers each other or the inorganic fibers with the organic fibers, thus obtaining a single-layer thermal insulating material (thermal insulating material body). This operation can be carried out by putting the formed article in an oven and heating and drying it at 170°C over five minutes, for example.

Then, the resulting thermal insulating material body is completely dried by using a drier. It is understood that the adhering and bonding of the organic fibers each other or the inorganic fibers with the organic fibers, initiated in the previous heating and drying step, are completed in the process of this final drying step. Then, at least one of the thermal insulating material body is coated with the above- described coating material by using a known and conventional technique, i.e. spraying or coating. Usually, at least one, preferably both surfaces, of the thermal insulating material body is/are coated after the coating material was diluted to two - ten times with a solvent (e.g. water or an organic solvent). Thus, a desired thermal insulating material can be obtained.

When using the thermal insulating material to retain the catalyst support, the formed article is optionally cut into a predetermined shape. Since the resulting thermal insulating layer is a single layer, a complicated production step is not required, like a multi-layer thermal insulating material, and the thermal insulating layer can be produced by a well-known and conventional procedure. This thermal insulating layer can retain the fixed shape without using a protective sheet as described in Japanese Unexamined Patent Publication (Kokai) No. 11-166414. Accordingly, this thermal insulating layer may be only disposed at the space between the metal casing and catalyst support without attaching or removing the protective sheet. That is, when using this thermal insulating layer, the catalytic converter can be easily assembled in a conventional manner without using any additional device.

Examples

The present invention will now be described with reference to its examples. The present invention is not limited to the following examples. Production of thermal insulating material Example 1

First, a coating material of polyacrylic acid (manufactured by NIPPON ZEON Co., Ltd. under the trade name of "LX-816", solid content of 42%) was diluted with water at a dilution degree of 5 time to prepare a coating solution. Both surfaces of a thermal insulating material body (manufactured by MITSUBISHI CHEMICALS Co., Ltd. under the trade name of "MAFTEC BLANKET") composed mainly of a laminated material of inorganic fibers of crystalline alumina were spray coated with the coating solution. The coating weight of the coating solution was controlled so that the weight of the organic matter containing the coating material is 1% or less based on the total weight. The coating solution was dried to obtain a thermal insulating material.

Example 2

In the same manner as in Example 1, except that both surfaces of the thermal insulating material body were coated with about 0.3 g of a coating solution (manufactured by ODEC Co. under the trade name of "SERACOAT 22-T") of an aqueous potassium phosphate solution by spraying and then dried, a thermal insulating material was made.

Example 3 In the same manner as in Example 2, except that both surfaces of the thermal insulating material body were coated with about 0.3 g of an aqueous potassium silicate solution and dried, and then further coated with about 0.3 g of a coating solution (manufactured by ODEC Co. under the trade name of "MASTER SEAL") of an aqueous aluminum phosphate solution by spraying, and then dried, a thermal insulating material was made.

Comparative Example 1

In this example, the thermal insulating material bodies used in Examples 1 to 3 were used as they are, for comparison. These thermal insulating material bodies are well known as a holding seal material for catalyst converter and have a bulk density of 0.09 to

0.11 g/cm³ and a tensile strength of 1000 to 1500 MPa. Example 4

First, a bulk material (manufactured by MITSUBISHI CHEMICALS Co., Ltd. under the trade name of "MAFTEC BULK") composed mainly of inorganic fibers of crystalline alumina was fibriUated in 47.6 g of water. These inorganic fibers were simply mixed in with 6 g of an inorganic binding medium composed of glass fibers

(manufactured by NIPPON PLATE GLASS Co., Ltd. under the trade name of "MICROGLASS") and 2.4 g of an inorganic aggregating agent composed of cepiolite during making of the thermal insulation material body, and then the mixture was formed into a mat by using a paper-making method. The resulting mat was pressed and dried. Then, both surfaces of the mat were coated with about 0.3 g of the coating solution of the aqueous potassium silicate solution used in Example 2 by spraying and dried. The mat coated with the coating solution was put in an electric oven at 800°C for one hour to obtain a thermal insulating material wherein inorganic fibers are fused as a result of softening of glass fibers.

Comparative Example 2

In the same manner as in Example 4, except that the mat was not coated with the coating solution by spraying for comparison, a thermal insulating material was made.

Example 5

In the same manner as in Example 4, except that the following mixture of a binding medium,, an aggregating agent and a paper strength enhancer was used in place of 6 g of the inorganic binding medium composed of glass fibers (microglass) and 2.4 g of the inorganic aggregating agent composed of cepiolite, a thermal insulating material was made.

(Binding medium)

Organic fibers (thickness: 0.11 g/km, manufactured by YUNITIKA FIBER Co., Ltd. under the trade name of "MELTY 4080")

Organic binder (trade name of "LX-816") (Aggregating agent)

Inorganic aggregating agent (Cepiolite) Organic aggregating agent (manufactured by MITSUI S AITEK under the trade name of "ACULAK 135")

Organic aggregating agent (manufactured by MITSUI S AITEK under the trade name of "ACULAK 304E") (Paper strength enhancer)

Product of HARIMA CHEMICALS Co., under the trade name of "HERMIDE B-15" The content of the organic matter in the aggregating agent and paper strength enhancer used herein was calculated. As a result, a total amount of the organic matter in ACULAK 135, CULAK 304E and HERMIDE B-15 was 3% based on the total weight of the thermal insulating material. Then, both surfaces of the resulting mat were coated with about 0.03 g of a coating solution of an aqueous potassium silicate solution by spraying and dried to obtain a thermal insulating material.

Comparative Example 3 In the same manner as in Example 5, except that the mat was not coated with the coating solution by spraying for comparison, a thermal insulating material was made.

Observation of thermal insulating material

The surface of the thermal insulating materials made in Examples 1 to 5 and Comparative Examples 1 to 3 was observed by using a scanning electron microscope. As a result, microphotographs (SEM photographs) shown in Figs. 2 to 9 were obtained.

As shown in Figs. 2 to 4, Fig. 6 and Fig. 8, the thermal insulating materials of Examples 1 to 5 have inorganic fibers laid down on the surface. Furthermore, it is also observed that the inorganic fibers are closely bonded each other through organic and inorganic binding mediums. Accordingly, such a thermal insulating material can prevent protrusion or scattering of inorganic fibers while the content of organic matters such as organic fibers and/or an organic binder is reduced to the same or higher degree as compared with a conventional catalytic converter. Thus, it is made possible to avoid an unpleasant feeling caused by direct contact of the thermal insulating material with the end portion of the inorganic fibers due to the above-described protrusion or scattering when the thermal insulating material is incorporated into the catalyst converter by the operator. A wrong operation of an exhaust gas purification system hardly occurs. Contrary to the above results, in the thermal insulating materials of Comparative Examples 1 to 3, the inorganic fibers raise a nap on the surface as shown in Fig. 5, Fig. 6 and Fig. 9. Accordingly, when such a thermal insulating material is incorporated into the catalyst converter by the operator, the thermal insulating material is directly contacted with the end portion of the inorganic fibers, thereby to impart an unpleasant feeling to the operator.

Evaluation tests of thermal insulating material

The thermal insulating materials produced in Examples 4 and 5 were evaluated with respect to the bulk density (g/cm³), the tensile strength (MPa), and the elongation

(%). The bulk density was determined as follows. That is, an average thickness of a sample obtained by cutting a thermal insulating material into a square having a side of 220 mm was determined from each thickness at five points, i.e. four points closer to corners and central one point, and then the above surface density was divided by the resulting average thickness to calculate the bulk density. After the thermal insulating material was cut into a rectangle having a width of 25 mm and a length of 180 mm, the stretching rate and elongation were measured at room temperature using an autograph manufactured by SHEVIADZU Corp. At this time, the stretching rate was controlled to 20 mm/minutes. It has been found that the thermal insulating material of Example 4 has a bulk density of 0.14 g/m³, a tensile strength of 0.034 MPa and an elongation of 0.9%. It has also been found that the thermal insulating material of Example 5 has a bulk density of 0.16 g/m³, a tensile strength of 0.045 MPa and an elongation of 3.39%. As is apparent from these measurement values, these thermal insulating materials have enough bulk density to hold the catalyst support, enough tensile strength and elongation to endure winding around the catalyst support while reducing the content of organic matters.

According the present invention there can be provided a thermal insulating material which is efficiently produced while the content of organic matters such as organic fibers and/or an organic binder is reduced to the same or higher degree as compared with a conventional catalytic converter, and which is applied to a catalyst converter while an unpleasant feeling to the operator is avoided as possible.

According to the present invention, there can be efficiently produced and provided a catalytic converter, which has high performances and does not cause a wrong operation of an exhaust gas purification system by using such an excellent thermal insulating material.

Claims

What is claimed is:

1. A thermal insulating material comprising: a thermal insulating material body formed of a bulk material of inorganic fibers; and a coating provided on at least one surface of said thermal insulating material body.

2. The thermal insulating material according to claim 1, wherein said coating is made of an organic polymer compound.

3. The thermal insulating material according to claim 1, wherein said coating is made of an inorganic compound.

4. The thermal insulating material according to any one of claims 1 to 3, wherein said thermal insulating material body further comprises an integrated component of inorganic fibers and said integrated component contains an organic matter in the amount of 3 wt% or less based on the total amount of said thermal insulating material body, said coating and said integrated component.

5. The thermal insulating material according to claim 4, wherein said integrated component further contains an aggregating agent.

6. The thermal insulating material according to any one of claims 1 to 3, wherein said thermal insulating material body further comprises an integrated component of inorganic fibers and said integrated component contains a binding medium of glass fibers

7. The thermal insulating material according to claim 6, wherein said integrated component further contains an aggregating agent.

8. A pollution control device comprising: a casing, a pollution control element disposed in said casing, and a thermal insulating material disposed between said casing and said pollution control element, characterized in that: said thermal insulating material comprises a thermal insulating material body formed of a bulk material of inorganic fibers, and a coating provided on at least one surface of said thermal insulating material body.

9. The pollution control device of claim 8, wherein said device is a catalytic converter and said pollution control element is a catalyst element.