JPH06239656A - Heat-insulating material for catalyst - Google Patents

Abstract

PURPOSE:To obtain the heat-insulating material comprising a multi-layered structure using a heat-insulating material extremely low in heat conductivity and excellent in durability on the high temperature side of a heat insulating wall and using an inorganic fiber heat- insulating material having good heat-insulating property, assembling property and restoring property at low temperatures on the low temperature side of the heat insulating wall without substantially using an organic material, excellent in the heat-insulating property, assembling property and durability, and useful for automotive exhaust gas-cleaning catalysts. CONSTITUTION:This heat-insulating material for automotive exhaust gas-cleaning catalysts is characterized by comprising a multi-layered structure material using (A) a heat-insulating material on the high heat temperature side of a heat-insulating wall and (B) one kind or more of heat-insulating materials on the low temperature side of the heat-insulating wall, where the heat-insulating material (A) comprises 1-50wt.% of ceramic inorganic fibers having an average fiber diameter of <=10mum, 40-98wt.% of one kind or more of inorganic powdery materials having an average refractive index of >=1.4 and an average particle diameter of <=10mum, and 1-20wt.% of an inorganic binder, and having a bulk density of 0.30-0.50g/cm<3>, and the heat-insulating material (B) consists mainly of inorganic fibers having a 50% compression load of <=1Kgf/cm<2> at the ordinary temperature.

Description

Detailed Description of the Invention

[0001]

2. Description of the Related Art Nonwoven fabrics such as glass fiber mats and ceramic fiber blankets made of silica-alumina fibers (for example, Ibiden Solid Blanket manufactured by IBIDEN Co., Ltd.) have been conventionally used as heat insulating materials for automobile exhaust gas purification catalysts. There is used a product obtained by punching an expanded shape and compressing it between a catalyst carrier and a metal case serving as an outer cylinder thereof.

In recent years, in order to improve fuel efficiency of automobiles, the exhaust gas temperature has been rising compared to the conventional one, and further, due to the tightening of exhaust gas regulations, one having a higher purification efficiency of an exhaust gas purifying catalyst is required. In the vicinity of the exhaust gas purifying catalyst, the temperature of the exhaust gas is higher than the exhaust gas temperature due to the heat of reaction. However, since the glass wool mat has a heat-resistant temperature of only 600 to 800 ° C., there is a problem that melting temperature and remarkable performance deterioration occur due to the high temperature of the exhaust gas. Further, since the ceramic affiber blanket made of the silica-alumina fiber has an excellent heat resistance temperature of 1260 ° C., it does not suffer the heat deterioration like a glass wool mat, but in a very limited space such as an automobile exhaust system part. In this case, it is not possible to simply increase the heat insulation thickness with respect to the above-mentioned high exhaust gas temperature, and the outer cylinder temperature of the exhaust gas purifying catalyst becomes high, and the surrounding electronic parts and rubber hoses There is a problem that not only is the heat damage caused by heat damage, but also when there is combustible material such as dead grass and cardboard in the lower part of the vehicle body when the vehicle is stopped after running, heat damage may cause a fire.

On the other hand, the inventors of the present invention have proposed Japanese Patent Application No. 4-2.
No. 2119, the ceramic-based inorganic fiber is 5 to 50
wt%, 50 to 95 wt% of inorganic powder, 3 to 5 wt% of inorganic binder and 3 to 10 wt% of organic elastic material as required.
%, And has a bulk density of 0.35 to 0.45 g
The present invention has invented a heat insulating material that has dramatically improved heat insulating properties and heat resistance as compared with the conventional heat insulating material by having a characteristic of having / cm ³ .

[0004]

However, the above conventional heat insulating material contains the organic elastic material in a proportion of 3 to 10 wt% in order to improve workability when it is assembled into an automobile exhaust gas purification catalyst. When this heat insulating material is used (when the engine of an automobile is actually started), the organic elastic material is gradually burned down, and not only the bad odor caused by the combustion gas rises, but also when the heat insulating material is used, the organic elastic material is burned out at the same time as heating, and after burning. Since the portion where the organic elastic substance was present becomes a void, the effect of scattering and blocking of radiant heat is lowered particularly at a temperature of 350 ° C. or higher, and it is concluded that the heat insulating property is insufficient. Therefore, the object of the present invention is to form a heat insulating material in accordance with the shape of the use site,
Moreover, it is another object of the present invention to provide a heat insulating material for an automobile exhaust gas purifying catalyst, which has improved heat insulating properties and improved compression assembling properties as compared with conventional products.

[0005]

[Means and Actions for Solving the Problems] In the structure of the heat insulating wall, 1 to 50 wt% of ceramic inorganic fibers having an average fiber diameter of 10 μm or less and an average refractive index of 1.4 or more are provided on the high temperature side. 40 to 98 wt% of one or more inorganic powders having an average particle diameter of 10 μm or less,
An inorganic binder is compounded in a ratio of 1 to 20 wt% and a heat insulating material having a bulk density of 0.30 to 0.50 g / cm ³ is arranged, and the low temperature side of the structure of the heat insulating wall. An insulating material for automobile exhaust gas purifying catalyst having a multi-layer structure in which one or two or more kinds of insulating materials having a 50% compression load at room temperature of 1 kgf / cm ² or less, which are mainly composed of inorganic fibers, are combined.

[0006]

Next, the structure of the present invention will be described in detail. First, in the structure of the heat insulating wall, the heat insulating material arranged on the high temperature side will be described. As the ceramic inorganic fiber, various whiskers such as silica-alumina fiber, alumina fiber, silica fiber, SiC whiskers and potassium titanate whiskers can be used. The amount of the ceramic inorganic fiber compounded is in the range of 1 to 50 wt%, and if this ratio is less than 1 wt%, the reinforcing effect of the fiber cannot be obtained, and the handleability and mechanical strength are significantly reduced.

On the other hand, if it exceeds 50 wt%, the amount of addition of the inorganic powder becomes small, and convective heat transfer, molecular heat transfer, radiative transfer, etc. increase, so that the heat insulating property remarkably deteriorates. Further, the average fiber diameter of the inorganic fibers needs to be 10 μm or less. This is because, in general, since inorganic fibers are rigid, if the average fiber diameter is larger than 10 μm, the voids between the fibers become large, and coarse voids are generated in the obtained heat insulating material, which facilitates the propagation of radiant heat. Is.

In the present invention, one kind or two or more kinds of inorganic powders satisfying the following conditions are selected and used. (1) The average refractive index is 1.4 or more. (2) The average particle size is 10 μm or less. (3) Solid thermal conductivity is 0.06 cal / c at room temperature
m. sec. As the powder having an average refractive index of 1.4 or more, which is deg or less, TiO ₂ , B
Examples thereof include aTiO ₃ and PbS. The inorganic powders in this group play a very important role as a scattering material for radiant heat, and in order to more effectively scatter radiant heat, the refractive index should be as high as possible. Large and wavelength of 10 μm
It is desirable to use an inorganic powder having a peak with a reflectance of 70% or more for the above light. Therefore, in the present invention, TiO ₂ having a rutile structure is used.

The inorganic powder used in the present invention has an average particle size of 10 μm or less, and the solid thermal conductivity of each powder is 0.06 cal / cm. sec.
It is limited to those having a degree of deg (at room temperature) or less. When a powder having an average particle size of 10 μm or more is used, the pores generated in the heat insulating material become extremely large, so that convection and molecular heat transfer increase, and the thermal conductivity deteriorates.
Also, the solid thermal conductivity is 0.06 cal / c
m. sec. If powder having a degree of deg (at room temperature) or more is used, solid heat transfer becomes dominant in the heat insulating material, and the thermal conductivity deteriorates. Therefore, in the present invention, one or two kinds of inorganic powders that meet the above-mentioned three conditions are used, and the compounding ratio thereof is in the range of 40 to 98 wt%. When the blending ratio of the inorganic powder is 40 wt% or less, the amount of the powder having a large refractive index is small, so that the scattering of radiant heat becomes insufficient and the thermal conductivity at a high temperature of 300 ° C. or higher deteriorates. Further, if it is 98 wt% or more, it is advantageous in terms of thermal conductivity, but the compounding ratio of the ceramic inorganic fiber or the like will be less than 2 wt%, resulting in a marked decrease in strength.

Next, in the present invention, an inorganic binder for the purpose of maintaining the strength at high temperature is added in an amount of 1 to 20 wt% if necessary.
It can be used in a range of. Examples of the inorganic binder include colloidal silica, synthetic mica, montmorillonite, etc.
Alternatively, it is used by impregnating the obtained heat insulating material. If the amount of the inorganic binder is less than 1%, the strength of the obtained heat insulating material will be insufficient, and if it is more than 20 wt%, the binding force between the binders causes segregation in the heat insulating material, resulting in other parts. Since coarse voids are generated, the thermal conductivity of the heat insulating material deteriorates.

A composition obtained by molding the composition blended in the above blending ratio into an arbitrary shape by a dry pressing method or a wet papermaking method has a bulk density of 0.30 to 0.50 g / c.
Within the range of m ³ . This bulk density is 0.30 g / cm ^3.
Below, convection and molecular heat transfer increase, while 0.50 g
If it exceeds / cm ³ , the solid heat transfer is increased and the thermal conductivity is significantly reduced.

In the above heat insulating wall structure, the thickness of the heat insulating material arranged on the high temperature side is the purpose of the outer skin temperature of the automobile exhaust gas purifying catalyst and the outermost circumference of the catalyst unit (generally a metal case). It may be decided depending on the temperature of. That is,
Since the heat insulating material is intended to scatter radiant heat at high temperatures, it is preferably used in a temperature range of about 400 ° C. or higher so that its effect is exhibited at higher temperatures. Next, a method for manufacturing the heat insulating material of the present invention will be described.

In the present invention, the heat insulating material is manufactured by a dry pressing method or a wet papermaking method. First, in the dry pressing method, after mixing the ceramic-based inorganic fibers, the inorganic powder and, if necessary, an inorganic binder with a V-type mixer or the like,
The mixture is put into a predetermined mold and pressed to obtain a molded body. In addition, it is also possible to impregnate the obtained molded body with an inorganic binder. Next, in the wet papermaking method, the ceramic-based inorganic fibers, the inorganic powder and, if necessary, the inorganic binder are dispersed in water, and then a very small amount of an aluminum sulfate aqueous solution or a polymer flocculant is added to the fibers to make them inorganic. Attach powder or inorganic binder. Next, the above-mentioned agglomerate is put into a predetermined mold and paper is made to obtain a molded body. The obtained heat-insulating material is obtained by subjecting the obtained molded body to dewatering press, adjusting the water content in the sheet to 100% or less, and then drying. Here, the water content of the sheet after the dewatering press is 10
It must be 0% or less, and if the water content is 100% or more, shrinkage occurs during drying and it becomes difficult to obtain a predetermined dimension.

In the heat insulating material obtained as described above, the strength is reinforced by the ceramic inorganic fiber, and when an inorganic binder is used, the strength at high temperature is maintained.
In addition, by using two kinds of inorganic powder suitable for the above conditions, air convection and molecular heat transfer in the voids inside the heat insulating material are suppressed, and further radiant heat is scattered, so that the heat insulation With respect to the property, it is possible to obtain properties superior to those of the conventional products.
Further, since the heat insulating material of the present invention does not contain an organic binder or the like, the organic matter is not burned out after heating and voids are not generated, so that extremely excellent heat insulating properties can be obtained from a low temperature to a high temperature as compared with the conventional case. Next, one type or two or more types of heat insulating materials arranged on the low temperature side in the structure of the heat insulating wall will be described.

As the inorganic fibers, of course, silica-alumina fibers, alumina fibers, silica fibers and the like are used, but since they are used in a low temperature range, fibers having low heat resistance such as glass wool and rock wool can also be used. However,
Silica-alumina fiber is preferable in consideration of abnormally high temperature. In the present invention, one of the reasons for making the structure of the heat insulating material a multi-layer structure is that on the high temperature side where radiation is dominant,
A heat insulator with low thermal conductivity using a radiation scattering material is used, and on the low temperature side where convection and conduction are dominant, a heat insulator with high heat insulating performance and mainly composed of inorganic fibers containing a relatively large amount of air is used. However, as another reason, the heat insulating material used on the high temperature side has an extremely poor compressibility because it contains an inorganic binder but does not contain an organic binder, as described above.

Usually, an automobile exhaust gas purifying catalyst unit has a ceramic catalyst carrier such as cordierite or 20
A stainless steel catalyst carrier made of Cr-5Al is housed in a metal case for use. Since the different parts have dimensional tolerances, the space (clearance) in which the heat insulating material is inserted is not always the same as in the present invention, and the automobile exhaust system parts are used for high speeds in parking in extremely cold areas and in extremely hot areas. It is used under conditions of extremely wide temperature range such as running. Under such a temperature range, the catalyst carrier and the metal case repeatedly expand and contract differently. In particular, when the cordierite catalyst carrier having an extremely small coefficient of thermal expansion is housed in a metal case, a remarkable change in clearance occurs.

Therefore, the heat insulating material for exhaust gas catalysts for automobiles is required to have not only heat resistance and heat insulating properties but also compression-restorability so as to be able to follow the dimensional tolerance at the time of assembling the parts and the clearance variation at the time of use. . That is, when a heat insulating material that is excellent in heat insulating performance at high temperature but extremely poor in compressibility is used alone, not only the heat insulating material is damaged during assembly of the parts or the case is deformed, but also the clearance during use is widened. If
The heat insulator vibrates and is damaged. Therefore, it is necessary to have a multi-layer structure with a heat insulating material having high compression-restoration as in the present invention, and the inventors have found that a 50% compressive load at room temperature is 1 Kgf.
It has been invented that the above-mentioned problems do not occur if a heat insulating material of less than / cm ² is used.

Desirably 0.2 to 0.5 Kgf / cm
Used in combination with the heat insulating material of ² . Considering the heat insulating effect, the thickness of the heat insulating material used on the low temperature side is 400
The temperature may be set to be less than 0 ° C., but it is preferable that the thickness is 1 mm or more when assembled in the automobile exhaust gas purification catalyst in view of the problem of compression-recovery ratio. Further, the constituent material may be one kind or two or more kinds, and considering the cost at the time of use, for example, as a three-layer structure in which a low-cost glass mat is used on the lower temperature side and silica-alumina fiber is used on the higher temperature side. Alternatively, under severer conditions such as vibration, silica-alumina fiber and silica cloth may be used.

The automobile exhaust gas purification catalyst heat insulating material obtained as described above has excellent strength and heat insulating properties in the high temperature region where radiant heat is dominant, and low temperature region where conduction and convection are dominant. In addition, not only the strength and heat insulating property are deteriorated, but also when the catalyst unit is assembled, since the 50% compressive load at room temperature is 1 Kgf / cm ² or less, the compression margin is extremely large and the durability is excellent. Insulation is obtained. Next, examples and comparative examples embodying the present invention will be described below.

[0020]

【Example】

(Example 1) 5 parts by weight of so-called bulk (Ibiden Co., Ltd .: trade name Ibiwool) as silica-alumina ceramic fiber in 50 liters of water in weight ratio, then average refractive index of 2.71 and average particle diameter. Is 3.5 μm T
70 parts of io ₂ powder and an average refractive index of 1.55,
20 parts of SiO ₂ powder having an average particle size of 7.0 μm, and further 5 parts of colloidal silica (manufactured by Nissan Chemical Co., Ltd .: trade name Snowtex) in a solid content weight ratio were added, mixed well, and then mixed in a very small amount. Of cationic polymer flocculant
The slurry was adjusted. Next, the slurry is molded into a half sleeve shape with a predetermined mold and then dried to have a thickness of 7 mm,
A heat insulating material having a bulk density of 0.40 g / cm ³ was obtained.

Further, a blanket of silica and alumina fibers (Ibiden Co., Ltd .: trade name Ibiwool Solid Blanket) thickness 6 mm, bulk density 0.10 g / cm, 5
A 0% compressive load of 0.3 Kgf / cm ² was punched out into a predetermined developed shape, and two pieces were attached to the heat insulating material to prepare two pieces. This two-layer structure heat insulating material was attached to a cylindrical metal catalyst carrier and then covered with a half metal case so that the clearance after assembly was 9.5 mm. The assemblability of this automobile exhaust gas purification catalyst unit was extremely good. Furthermore, this unit was mounted on an actual gasoline vehicle, the exhaust temperature was adjusted so that the innermost layer temperature of the heat insulating material was 900 ° C, and the temperature outside the metal case, which was the outermost layer, was measured and found to be 250 ° C.

Also, after carrying out 1000 cycles of a simple endurance test with 600 rpm-5 minutes and 5000 rpm-5 minutes as one cycle in a state where the above-mentioned unit was mounted on a vehicle, it was analyzed. There was no damage to him.

(Comparative Example 1) A silica-alumina fiber blanket having a thickness of 12.5 mm, a bulk density of 0.13 g / cm ³ , a 50% compressive load, and a pressure of 0.5 Kgf / cm ² was used as a heat insulating material in the same catalyst unit as in Example 1. When the same evaluation as in Example 1 was performed using, the assemblability was not a problem, but when the temperature of the innermost layer of the heat insulating material was 900 ° C., the temperature of the outer side of the metal case serving as the outermost layer was 480 ° C. .

(Comparative Example 2) A half-sleeve shaped article of Example 1 having a thickness of 10. mm, bulk density 0.40 g / cm ³ , 50% compressive load, 1.1 Kgf / cm ² I tried to assemble the heat insulating material, but the pressure was insufficient with the normal assembly equipment, and it could not be assembled, and it was assembled using the hydraulic press. As a result, the catalyst carrier was deformed.

[0025]

According to the present invention, therefore, not only does the conventional product not have poor heat insulation properties at high temperatures, but it not only exhibits extremely excellent heat insulation properties from low temperatures to high temperatures, but There is no problem in assembling and durability, and the workability is improved by preliminarily molding into a predetermined shape. Further, since the thermal conductivity is low, the thickness can be made thinner than the conventional product, so that the exhaust system component can be downsized. Furthermore, according to the present invention, since almost no organic matter is used in the conventional heat insulating material,
Not only does the thermal conductivity change with time, but there is no concern that it will pollute the environment because no gas is generated due to the combustion of the organic binder during use.

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Claims (4)

[Claims] 1. In the structure of a heat insulating wall, 1 to 50 wt% of a ceramic inorganic fiber having an average fiber diameter of 10 μm or less, an average refractive index of 1.4 or more, and an average particle diameter on the high temperature side thereof. 40 to 98 wt% of one kind or two or more kinds of inorganic powder having a particle size of 10 μm or less, and 1 to 20 w of an inorganic binder.
It is compounded at a ratio of t% and has a bulk density of 0.30 to 0.50.
A heat insulating material having a heat insulating material having g / cm ³ and having a 50% compressive load at room temperature of 1 kgf / cm ² or less, which is mainly composed of inorganic fibers on the low temperature side of the structure of the heat insulating wall. A heat insulating material for an automobile exhaust gas purifying catalyst, which has a multi-layer structure in which one kind or a combination of two or more kinds. 2. Silica-alumina fiber, alumina fiber,
The ceramic-based inorganic fiber according to claim 1, which is used on the high temperature side in the constitution of the heat insulating wall, including various whiskers such as silica fiber and potassium titanate whiskers. 3. The solid thermal conductivity at room temperature is 0.06 cal.
/ Cm. sec. The inorganic powder according to claim 1, which has a degree of deg or less. 4. The heat insulating material for a vehicle exhaust gas purifying catalyst according to claim 1, wherein the purpose of the heat insulating material is to heat and keep heat of a ceramic or metal catalytic converter for purifying an automobile exhaust gas.