JPH06299846A - Flexible and thermally expansilble sheet - Google Patents

Abstract

(57) [Summary] [Purpose] To obtain a sealing material for holding a ceramics monolith for purification that does not suffer wind erosion due to exhaust gas. A flexible heat-expandable sheet comprising a heat-expandable vermiculite, a heat-resistant inorganic fiber, and an organic binder, wherein at least a part of the heat-resistant inorganic fiber has a fiber length of 5 to 30 mm and a fiber diameter of 3 to. A flexible thermally expandable sheet containing 10 to 50% by weight of long fibers in the range of 30 μm based on the entire sheet.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flexible thermal expansion sheet, particularly a ceramic body for purifying exhaust gas of automobiles, specifically a catalyst carrier, a porous filter, etc., in a metal container (casing). Easy to put in, and when exhaust gas passes, it fills the gap in the cross-sectional direction between the two, which is caused by the difference in thermal expansion between the ceramic body and the metal container, and the exhaust gas is discharged without being purified. The present invention relates to a flexible heat-expandable sheet which is suitable for use in a seal structure for preventing the formation of a bypass flow path that is formed and holding a ceramic body even under vibration of an automobile.

[0002]

2. Description of the Related Art As a vehicle exhaust gas purifying apparatus, a honeycomb catalyst carrier made of ceramics or a black smoke trapping material for a diesel engine vehicle is used. These are used by assembling a ceramics monolith in a metal container. When exhaust gas starts to flow when the engine is started, the heat causes the metal container and the ceramics monolith to thermally expand. However, the thermal expansion coefficients of the two are significantly different, and the value is larger in the metal container. Therefore, when the vehicle is operating, a void is formed in the cross-sectional direction between the metal container and the ceramic monolith.

Therefore, there arises a problem that the ceramic monolith plays or breaks in the metal container due to the vibration of the automobile. In order to solve this problem and prevent the formation of a so-called bypass passage, in which exhaust gas that has not been purified flows through this gap,
A flexible thermal expansion sheet is mounted between the metal container and the ceramic monolith during assembly.

This flexible heat-expandable sheet is made of heat-resistant inorganic short fibers (fiber length of about 2 to 3 mm) such as asbestos and silica / alumina (SiO ₂ · Al ₂ O ₃ ) and heat-expandable flint. Further, it is generally composed of an organic binder. Usually produced by the papermaking method, the face-plate-shaped heat-expandable vermiculite is deposited parallel to the plane direction of the sheet.
Therefore, the sheet itself, due to the expansion behavior of vermiculite,
It swells only in the thickness direction of the sheet. The expansion behavior of vermiculite itself is a well-known phenomenon, and it is known to start by a dehydration reaction from 600 ° C.

A rubber-based resin is mainly used as the organic binder, which imparts flexibility when the sheet is wound around the outer periphery of the ceramic monolith having a circular or elliptical cross section. It works to give flexibility.

However, the conventional flexible heat-expandable sheet has a cushioning property at high temperature and uses heat-resistant inorganic short fibers to hold the flint, but it is exhausted at high temperature. If you are exposed to the flow of gas for a long time,
There is a problem in that the short fibers are scattered and lose their role in initially holding the ceramic monolith and preventing the formation of an exhaust gas bypass passage. In addition, with the exhaust gas of automobiles, these scattered short fibers are released into the atmosphere, which is also a cause of environmental pollution.

[0007]

The present invention solves the problems of the prior art and is particularly suitable as a sealing material for holding ceramics monoliths for purification, which does not cause wind erosion by exhaust gas. An object is to provide a flexible heat-expandable sheet.

[0008]

The present invention is a flexible heat-expandable sheet comprising a heat-expandable vermiculite, a heat-resistant inorganic fiber, and an organic binder, wherein the fiber length is at least part of the heat-resistant inorganic fiber. Is 5 to 30 mm and the fiber diameter is in the range of 3 to 30 μm.
A flexible thermally expandable sheet containing 0% by weight is provided.

The present invention has a fiber length of 5 to 5 at least in part.
A heat-resistant inorganic fiber, which is a long fiber (hereinafter, simply referred to as a long fiber) having a diameter of 30 mm and a fiber diameter of 3 to 30 μm,
It is molded with a heat-expandable vermiculite and an organic binder. The long fibers are intricately entangled with each other in the sheet to impart durability against wind erosion due to exhaust gas.

The length of the long fibers must be in the range of 5 to 30 mm. If the length of the long fibers is less than 5 mm, the effect of blending the long fibers will not be exhibited, and the wind erosion resistance of the flexible thermal expansion sheet will not be sufficiently improved, such being unsuitable.
When the length of the long fiber exceeds 30 mm, the wind corrosion resistance is not further improved, and there is a problem that handling of the long fiber becomes difficult at the time of production, which is not suitable. When the length of the long fibers is 10 to 30 mm, the effect of further strengthening the entanglement of the fibers is obtained, and the wind erosion resistance is particularly good, which is preferable.

The diameter of the long fibers should be in the range of 3 to 30 μm. When the diameter of the long fibers exceeds 30 μm, the flexibility of the fibers is lost and the fibers cannot be entangled with each other, which is not suitable. If the diameter of the long fibers is less than 3 μm, it is difficult to disperse the long fibers in the flexible heat-expandable sheet, and it becomes difficult to produce continuous long fibers. . When the diameter of the long fibers is in the range of 10 to 20 μm, the breaking load of the long fibers becomes large, and the reinforcing effect of the flexible thermally expandable sheet is increased, which is more preferable.

The material of the long fibers can be appropriately selected according to the temperature range used, but as the composition of the long fibers which is stable at the exhaust gas temperature of a gasoline vehicle of 600 to 900 ° C., a general glassy fiber is used. Moreover, high siliceous fibers are useful at higher temperatures. Typical examples of this are E-glass, which is the most commonly used glassy fiber, and at higher temperatures, reachd silica fiber obtained by extracting Ca and Mg in E-glass with acid, or quartz glassy fiber. can give. Further, in the case of the black smoke trap collecting material of a diesel vehicle, a high alumina fiber stable at a temperature of 1200 ° C at which the collected black smoke abnormally burns is useful.

The fibrous material having the above-mentioned shape is difficult to obtain from mineral fibers such as asbestos, or fibers produced by blowing or spinning such as glass wool, and even if spun, its characteristics are difficult to obtain. When continuously producing long fibers, when produced by a method of cutting appropriately,
It is preferable because it can be easily obtained and the length can be easily controlled.

The blending amount of the long fibers must be in the range of 10 to 50% by weight based on the total weight of the flexible heat-expandable sheet. When the blending amount of the long fibers is less than 10% by weight, it is difficult to effectively exhibit wind erosion resistance, which is unsuitable.
If the blending amount of the long fibers exceeds 50% by weight, problems such as insufficient expandability and insufficient exhaust gas sealability occur, which are not suitable. 20 to 4 long fiber content
It is more preferable if it is 0% by weight.

The heat resistant inorganic fibers may include not only the above long fibers but also short fibers. As the short fibers, silica / alumina-based crystalline fibers are preferably used. The blending amount of the long fibers with respect to the entire heat resistant inorganic fibers is preferably 20 to 80% by weight.

The compounding ratio of the heat-resistant inorganic fiber as a whole, the heat-expandable vermiculite and the organic binder must be determined from wind erosion resistance, heat-expansion force and flexibility. It is preferable that the heat-resistant inorganic fibers are in the range of 30 to 50% by weight, the heat-expandable flint is in the range of 40 to 70% by weight, and the organic binder is in the range of 5 to 10% by weight with respect to the entire sheet. It may contain other additive components, water used in the manufacturing process, a thickener, and the like.

In the present invention, the heat-expandable vermiculite is a vermiculite (such as vermiculite) whose crystal can be expanded by heating, and preferably has an average particle diameter of about 0.2 to 3 μm. The organic binder exhibits softness such that the outer periphery of the ceramic monolith can be wound, and examples thereof include a rubber resin.

As the method for producing the flexible heat-expandable sheet of the present invention, heat-resistant inorganic fibers (long fibers and, if necessary, short fibers such as silica / alumina), heat-expandable flint and organic binder are used. The papermaking method is suitable because it can be dispersed well and uniformly and can be orientated and deposited so that the scales expand in the thickness direction. Generally, in a papermaking method, fibers are dispersed in water, but what is important in the present invention is that long fibers are well opened in water. For that purpose, it is preferable that the monofilament sizing material applied when producing the long fibers is water-soluble.

Another important point is that fibers and vermiculite do not separate due to the difference in specific gravity. For that purpose, it is preferable to use, as the dispersion medium (papermaking mother liquor), water which has been increased in viscosity by adding a water-soluble organic substance (thickener) such as methyl cellulose or polyvinyl alcohol. The viscosity at that time is preferably 100 to 500 cP in terms of 15 ° C., since there is no precipitation of vermiculite and there is no hindrance to the subsequent production efficiency. The organic binder is preferably added in the step of preparing the papermaking mother liquor.

Heat-resistant inorganic fibers and heat-expandable vermiculite are added to the papermaking mother liquor thus prepared with stirring. As the long fibers, it is preferable to use chopped strands obtained by cutting a bundle of long fibers coated with a water-soluble sizing material into a predetermined length. In order to efficiently open the fibers, it is also preferable to separate a part of the papermaking mother liquor, add a fiber material therein, and preliminarily disperse it by adding mechanical stirring or the like. . At this time, the predispersed liquid is returned to the papermaking mother liquor again, and the process proceeds to the next papermaking step.
Add a suspension of heat-resistant inorganic fibers and heat-expandable vermiculite to 1
When it is poured into a metal mesh sheet of about 0 mesh and the liquid content is filtered, the solid substance consisting of heat-resistant inorganic fiber, heat-expandable flint stone, organic binder, and thickener is finally obtained as a filtration residue. can get.

The obtained solid substance still contains water, and the filling of the heat-resistant inorganic fiber and the heat-expandable vermiculite is coarse per volume, so that it is bulky. Therefore, in order to obtain a desired thickness and bulk density, it is preferable to press and dry the filtration residue while heating to obtain a flexible heat-expandable sheet. In actual use, cut to the desired size and assemble. It is clear that the organic binder and the thickener burn at a relatively low temperature, and the heat-resistant inorganic fiber and the expanded vermiculite are stable at a temperature equivalent to exhaust gas.

In the performance evaluation of the flexible heat-expandable sheet, the engine of a real car is connected to a catalytic converter in which the flexible heat-expandable sheet of the present invention is assembled, and the engine is operated under predetermined conditions. Although it becomes clear by rotating, wind erosion resistance can be easily known by the method described below.

For example, to obtain a 7 mm-thick flexible heat-expandable sheet, after cutting it into a predetermined area, the sheet is sandwiched between two heat-resistant stainless steel plates, and the ceramic monolith and metal Tighten up to the expected gap during thermal expansion between the containers, for example, 5 mm. In this state, heat treatment is performed at a predetermined temperature for a predetermined time, and after the heat treatment, the product is taken out of the furnace. As an evaluation of wind erosion resistance, compressed air much higher in pressure than exhaust gas entering the catalytic converter, for example,
This is a method in which air having a pressure of 4 to 6 kg / cm ² is blown onto the thickness surface of the sheet with an air gun spaced a certain distance, and the amount or area of wind erosion in a predetermined time is examined.

As a means for evaluating the degree of entanglement of the long fibers, the breaking load (tearing load) of the strip-shaped sheet after the heat treatment performed in the same manner can be mentioned. Naturally, the stronger the entanglement of the long fibers, the larger the tear load.

[0025]

【Example】

Example 1 15 g of methylcellulose was dissolved in 2500 g of water to prepare a viscous liquid having a viscosity of 400 cp at 20 ° C., and an SBR latex (solid content 70%) 300 as an organic binder was added thereto.
g is added and mixed to obtain a papermaking mother liquor. 17 g of unexpanded spinach was added to this papermaking mother liquor, and the mixture was stirred and dispersed, and then the fused silica glass long fibers (average diameter 13 μm) were 12 m in length.
11 g of chopped strands cut into m were added and stirred to disperse. The obtained suspension is filtered through a 10-mesh wire net to obtain a filtration residue having a diameter of 11 cm and a thickness of 10 mm.
A water-containing sheet on a circular plate was obtained. The hydrated sheet was squeezed by a press to a thickness of 6 mm and dried at 90 ° C. to obtain a flexible thermally expandable sheet which is a final product having a bulk density of 0.57 g / cc. In this sheet, 37.
1% by weight, 55.1% by weight of thermal expansive syenite, and 6.7% by weight of organic binder were contained. The balance is mainly water.

A 5 cm square was cut out from the obtained sheet,
Using this as a test piece, a stainless steel plate (100 mm × 100
(mm × 5 mm thickness) The two sheets were tightened to a thickness of 5 mm. 1 at 800 ℃ with the stainless plate tightened
After heat treatment for 5 minutes, it was cooled. An air gun nozzle (caliber 3 mm) was installed at a position 2 cm away from the gap between the two stainless steel plates toward the thickness surface of the test piece, and compressed air (source pressure 6 kg / cm ² ) was blown for 30 seconds. . After spraying, when the test piece was removed from the stainless steel plate,
The depth eroded by the spraying was 1 mm.

Example 2 As long fibers, 5.5 g of chopped strands of quartz glassy long fibers and 5.5 g of silica / alumina short fibers (trade name Kao Wool, manufactured by Isolite Kogyo) were used as short fibers. A flexible thermally expandable sheet was obtained in the same manner as in Example 1. In this sheet, long fibers are 18.
2% by weight, 18.2% by weight of short fibers, 54.5% by weight of thermal expansive syenite, and 8.3% by weight of organic binder. The balance is mainly water. Further, when compressed air was blown in the same manner as in Example 1, the depth of wind erosion was 4 mm.

Example 3 The same procedure as in Example 1 was repeated except that 5.5 g of E glass fiber chopped strands having a length of 13 mm were used as long fibers and 5.5 g of silica / alumina short fibers were mixed and used. A flexible thermal expansion sheet was produced. In this sheet,
The composition contained 17.0% by weight of long fibers, 17.0% by weight of short fibers, 57.5% by weight of heat-expandable vermiculite, and 7.8% by weight of organic binder. The balance is mainly water. The wind corrosion resistance was evaluated in the same manner as in Example 1. The depth of wind erosion is 5
It was mm.

Comparative Example A sheet made of commercially available short silica / alumina fibers containing no long fibers, unexpanded vermiculite, and an organic binder (thickness: 6 mm,
A bulk density of 0.6 g / cc) was heat treated in the same manner as in Example 1 and blown with compressed air.
It was 8 mm.

[0030]

When the flexible thermal expansion sheet of the present invention is used in an exhaust gas treatment device, it is hard to be eroded by the exhaust gas, holds the ceramic monolith for a long time, and bypasses the exhaust gas which is not purified. The formation of flow channels can be prevented, and CH and NO released into the atmosphere
The concentrations of _x and SO _x can be suppressed. Similarly, the rate at which the fibers are released is reduced.

Claims (4)

[Claims] 1. A flexible heat-expandable sheet comprising a heat-expandable vermiculite, a heat-resistant inorganic fiber and an organic binder, wherein at least a part of the heat-resistant inorganic fiber has a fiber length of 5 to 30 mm and a fiber diameter. A flexible heat-expandable sheet containing 10 to 50% by weight of long fibers in the range of 3 to 30 μm based on the entire sheet. 2. A fiber length of 5 to 30 mm and a fiber diameter of 3 to 3
The long fibers within the range of 0 μm are 20 to 20% of the heat resistant inorganic fibers.
The flexible thermally expandable sheet according to claim 1, which is 80% by weight. 3. A seal structure for an automobile exhaust gas treatment device, which uses the flexible thermal expansion sheet according to claim 1. 4. A suspension containing heat-expandable vermiculite, a heat-resistant inorganic fiber, and an organic binder, which is 20 to 8 of the heat-resistant inorganic fiber.
0% by weight has a fiber length of 5 to 30 mm and a fiber diameter of 3 to 3
A method for producing a flexible heat-expandable sheet by molding a suspension in the range of 0 μm by a papermaking method.