JPH0647498B2 - Method of manufacturing curved thin plate ceramics - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a ceramic having a novel shape, and the ceramic obtained by the present invention can be used as a catalyst carrier substrate or a general-purpose structural material. .

2. Description of the Related Art Conventionally, a ceramic having a honeycomb structure extruded is generally used as a substrate for a catalyst carrier. This manufacturing method is an extrusion molding in which an appropriate amount of a molding aid and water are added to an inorganic heat resistant material. After that, it was obtained by cutting into a predetermined size, sufficiently drying, and then firing to a predetermined temperature to sinter the inorganic heat resistant material.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention In the conventional method for manufacturing a substrate for a catalyst carrier, only honeycomb ceramics having a planar shape can be obtained, and curved thin plate ceramics having a large degree of freedom and thin ceramics having a wide range of applications can be easily prepared. It was difficult to manufacture.

Means for Solving the Problems The present invention comprises (1) an inorganic heat-resistant material consisting of at least rehydratable alumina, fused silica, and potassium titanate, a binder that gels at a certain temperature or higher, and a plasticizer. The formed honeycomb body is dipped in hot water at a temperature at which the binder is gelated or higher, and after the honeycomb formed body exhibits flexibility, the honeycomb formed body is placed on a heat-resistant jig having a curved shape. It is placed or sandwiched between curved heat-resistant jigs, pre-baked at 1050 to 1150 ° C., then transferred onto a curved heat-resistant jig having a smaller radius of curvature than the heat-resistant jig, and then placed thereon. While applying a load from 120
A method for producing a thin plate ceramic having a curved shape, characterized by firing at 0 to 1300 ° C., (2) a curved shape in which the binder is selected from the group consisting of methylcellulose, hydroxypropylmethylcellulose and hydroxypropylcellulose (3) A method for producing a thin plate ceramic having a curved shape in which the plasticizer is selected from the group consisting of sorbitan acid ester and polyolefin glycol ether, and (4) the inorganic heat resistant material is Rehydratable Alumina 5-3
A method for producing a curved thin plate ceramic having a composition of 0 wt%, potassium titanate 2 to 7 wt%, and fused silica 68 to 93 wt%.

Action The present invention has the above-described structure, and can produce a substrate for a catalyst carrier having various shapes by an easy method by compounding a curved thin plate ceramic or a composite thereof. As a result, it can be expected to expand applications and improve characteristics in fields where honeycomb ceramics have been conventionally used.

Specifically, a molded body composed of an inorganic heat-resistant material consisting of at least rehydratable alumina, fused silica, and potassium titanate, and a binder and a plasticizer that gel at a temperature higher than a certain temperature is first formed. The molded body is made to exhibit flexibility by immersing it in hot water at a temperature not lower than that. By this step, when the molded body is subsequently placed on a heat-resistant jig having a curved shape, the molded body has an appropriate degree of flexibility to follow the curved shape.

Here, a binder (about 3
It is a water-soluble substance in water at 0 ° C or lower, but refers to a substance that causes gelation of the substance when the temperature exceeds a certain temperature). Specifically, cellulose ether-based substances are known, such as methylcellulose and hydroxypropyl. Examples include methyl cellulose and hydroxypropyl cellulose. For example, in the case of Metroses 60SH-4000 (Shin-Etsu Chemical, trade name),
It becomes hydrated at low temperatures. However, at 60 ° C. or higher, the gelation phenomenon suddenly occurs. As a result, the honeycomb molded body containing Metroze 60SH-4000 exhibits mechanical strength sufficient to maintain sufficient shape retention even in hot water. The mechanical strength depends on the amount of binder added and the temperature of hot water.

Further, the plasticizer in the present invention also when the above-mentioned honeycomb molded body is immersed in hot water at a temperature at which the binder gels or higher,
It is a material that can give flexibility to the molded product, and specific examples thereof include sorbitan acid ester and polyolefin glycol ether. When the molded product is immersed in hot water at a temperature higher than the gelling temperature, the molded product has a mechanical strength which is more than sufficient for the purpose of the present invention, under the condition that the plasticizer is not added to the molded product. However, if the molded body is then forcibly processed into a curved shape, cracks will occur in the molded body. Further, if the amount of the plasticizer added is too large, the flexibility in hot water increases too much, and handling during the manufacturing process becomes difficult. Further, comparing sorbitan acid ester with polyolefin glycol ether, sorbitan acid ester contributes more to the flexibility of the molded body.

As described above, the binder and the plasticizer in the present invention play a very important role, and they have a close mutual relationship. Therefore, it is necessary to select appropriate binders and plasticizers and determine the addition amounts thereof in consideration of the target shape and the like.

Next, the molded body exhibiting an appropriate degree of flexibility is placed on a heat-resistant jig having a curved shape, or sandwiched between heat-resistant jigs having a curved shape, and prebaked at 1050 to 1150 ° C. This step is called first firing. This step is unnecessary if the radius of curvature of the curved thin plate ceramic to be obtained is not small. However, in the case of a thin ceramics having a small radius of curvature as intended by the present invention, for example, a thin plate ceramic having a diameter of 30 mm or less, if the flat honeycomb is bent to a desired shape in one step, the product yield will be extremely deteriorated. Alternatively, it was difficult to obtain the target product.
Therefore, this step has the following meanings.

The binder, the plasticizer and the like are burned and removed from the honeycomb formed body during the firing process. The molded body (3
What is baked at 00 to 1050 ° C) is very fragile, and if it is transferred onto a curved heat-resistant jig or the like in this state, it will be broken during the process or the heat-resistant jig will be broken. When it is placed on the substrate, stress is applied to the molded body and cracks occur. However, the molded product of the present invention gradually starts to be sintered at around 1050 ° C. and has a certain degree of mechanical strength. So after that,
Even if it is placed on the next heat-resistant jig having a curved shape with a smaller radius of curvature, the molded body will not crack and will be able to withstand a certain load.

Next, it is transferred onto a heat-resistant jig having a desired curved shape with a smaller radius of curvature than the heat-resistant jig used in the above-mentioned first firing, and a load is applied from above onto the heat-resistant jig. Baking is performed at 1200 to 1300 ° C. This step is second
Baking.

In this process, the ceramic gradually sinters and is liable to be plastically deformed by the load from above. As a result, the obtained thin-plate honeycomb ceramic has a shape along the target heat-resistant jig having a curved shape.

In the present invention, it is preferable to use a ceramic composed of rehydratable alumina, fused silica and potassium titanate. At 1150 ° C. or higher, this ceramic becomes a solid solution phase of alumina and potassium titanate at the fused silica grain boundary and has excellent mechanical strength. In addition, the fused silica used also has a low thermal expansion characteristic. However, at 1300 ° C. or higher, fused silica is eroded in this solid solution phase and a part thereof is crystallized as cristobalite, which deteriorates the thermal shock resistance (low thermal expansion property) of ceramics. Therefore, the firing temperature is 120
It is preferable to carry out at 0 to 1300 ° C.

The rehydratable alumina used in the present invention means transitional alumina other than α-alumina obtained by thermally decomposing alumina hydrate, such as ρ-alumina and amorphous alumina.
Industrially, for example, an alumina hydrate such as alumina trihydrate obtained from the Bayer process is usually contacted with a hot gas at about 400 to 1200 ° C. for several minutes, or the alumina hydrate is reduced to about 250 to about 250 ° C. About 0.5 ~ which can be obtained by heating and holding at 900 ° C for 1 minute to 4 hours
Those having an ignition loss of 15% by weight are included.

The potassium titanate used in the present invention includes potassium tetratitanate and potassium hexatitanate, and fibrous ones are preferable. This is because a fibrous material (aspect ratio of 10 or more) can have a larger pore volume, and a ceramic material having excellent thermal shock resistance and excellent mechanical strength can be obtained.

The fused silica used in the present invention has a coefficient of thermal expansion of 0.5 × 10 ^−6.
/ ° C, which is very small. However, when impurities are mixed in the melting and crushing steps, the coefficient of thermal expansion increases, and the thermal shock resistance of ceramics deteriorates. Further, the physical properties of fused silica differ depending on the speed of cooling from the molten state. For example, ceramics having a slow cooling speed are likely to be crystallized (cristobalite) during use in a high temperature atmosphere as ceramics and deteriorate thermal shock resistance. Therefore, it is necessary to select one having a small amount of impurities and a small coefficient of thermal expansion.

Using these materials, the preferred composition of the present invention is 5 to 30 wt% rehydratable alumina and 2 to 7 w potassium titanate.
Ceramics composed of t% and fused silica 68 to 93 wt%. The reason is that the amount of rehydratable alumina added is 5w.
This is because the mechanical strength of the obtained ceramics becomes poor at t% or less, and the shrinkage rate of the obtained ceramics becomes large at 30 wt% or more, and the plastic deformation into the size and shape to be obtained becomes too large. Further, when the amount of potassium titanate used is 2 wt% or less, the mechanical strength of the obtained ceramic is poor, and when it is 7 wt% or more, extrusion molding is difficult because the potassium titanate material is a fibrous material having a large aspect ratio. This is because

According to the present invention, the thin ceramics having a curved shape can be manufactured with good workability and productivity by the above-described actions.

Example A method for manufacturing a curved thin-plate ceramics according to an example of the present invention will be described below.

(Example 1) 10 parts by weight of rehydratable alumina, 85 parts by weight of fused silica, 5 parts by weight of potassium hexatitanate and 6 parts by weight of Metroze 60SH-4000 (trade name, Shin-Etsu Chemical Co., Ltd.) as a binder. Then, 1.5 parts by weight of sorbitan acid ester as a plasticizer and water are added, the mixture is wet-kneaded, extrusion-molded, and then dried by a dielectric heating method, 200 mm × 50 mm, length 1
50 mm, cell density 90 cells / in ² (cell pitch 2.5 m
A honeycomb molded body having m and a rib thickness of 0.03 mm was obtained. afterwards,
The honeycomb molded body was cut into a thickness of 2.5 mm to obtain a flat-plate-shaped thin honeycomb molded body 1 as shown in Fig. 1 (a).

Next, as shown in FIG. 1 (b), the thin honeycomb molded body 1 is immersed in hot water 2 at 75 ° C. containing 0.1 wt% of an anionic surfactant for 10 minutes to form a binder (Metroze). 60SH-4000) was gelated, and the honeycomb formed body 1 was made to exhibit flexibility by a plasticizer. Thereafter, as shown in FIG. 1 (C), the honeycomb formed body 1 was sandwiched by a pair of curved heat-resistant jigs 3 and 4 so that a curved surface having a radius of curvature of 25 mm was formed. Next, after being dried as it is at 120 ° C. for 10 minutes, 1000 to 1
It heat-processed at 200 degreeC (1st baking) for 1 hour. Then, as shown in FIG. 1 (d), it is transferred onto a 13 mm heat-resistant jig 5 having a smaller radius of curvature than the heat-resistant jigs 3 and 4, and a pressing jig 6 made of a heat-resistant material is placed thereon. While applying a load, heat treatment was further performed at 1100 to 1350 ° C. (second baking) for 1 hour (FIG. 1 (e)). The results are shown in Table 1.

Here, ○ is a thin plate ceramics 7 having a desired shape.
(FIG. 1 (f)) was obtained, Δ was insufficient to bend the thin plate ceramics 1 to the desired shape, and × was cracks in the thin plate ceramics 1 or physical properties of the ceramics. There was a problem with.

As a result, when the first firing temperature is 1000 ° C., cracks occur in the thin plate ceramics 1, and the second firing temperature is 1350 ° C.
Then, there was a problem with the physical properties of the ceramics. Further, when a difference of about 150 ° C. or more was provided between the first firing temperature and the second firing temperature, the thin plate ceramics 7 having the target shape was obtained.

In order to explain the reason for this, the relationship between the heat treatment temperature and the mechanical strength of the ceramic obtained by firing a molded body having the same composition as in Example 1 was investigated. The results are shown in Table 2 and Table 2.
Shown in the figure. The mechanical strength is represented by the compressive strength in the honeycomb lattice direction of honeycomb ceramics cut into 10 mm × 10 mm × 10 mm.

As is clear from this, the ceramics of this composition are 110
Sintering rapidly progresses from around 0 ° C. Therefore, the first firing temperature in the present example means a transitional temperature range in which the ceramic has begun to sinter a little and the mechanical strength has not increased so much yet.

(Comparative Example) The flat plate-shaped honeycomb molded body 1 having a thickness of 2.5 mm obtained in the above-mentioned example was used, and the anionic surfactant was 0.1 w.
The binder (Metroze 60SH-4000) was gelated by immersing it in hot water containing t% at 75 ° C. for 10 minutes, and at the same time, the honeycomb formed body 1 exhibited flexibility due to the plasticizer. Then, this honeycomb formed body was sandwiched by curved heat-resistant jigs having a radius of curvature of 13 mm to form a curved surface. Next, it was dried as it was at 120 ° C. for 10 minutes.

As a result, the honeycomb molded body 1 was cracked during drying.

Effects of the Invention According to the present invention, it is possible to easily manufacture a curved thin-plate honeycomb ceramic, particularly a thin-plate honeycomb ceramic having a small radius of curvature.

In addition, by compounding them, it is possible to manufacture various shapes of catalyst carrier substrates with good processability and productivity.

[Brief description of drawings]

1 (a) to 1 (f) are views showing a manufacturing process of a curved thin-plate ceramics according to an embodiment of the present invention, and FIG.
The figure is a relationship diagram between the heat treatment temperature and the mechanical strength in the same process. DESCRIPTION OF SYMBOLS 1 ... Thin plate honeycomb molded body, 2 ... Hot water, 3 ... Retaining heat-resistant jig, 4 ... Retaining heat-resistant jig, 5 ... Retaining heat-resistant jig, 6 ... Retaining heat-resistant jig, 9 ... Curved thin-plate ceramics.

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Claims (4)

[Claims] 1. A honeycomb formed body comprising at least an inorganic heat-resistant material comprising rehydratable alumina, fused silica and potassium titanate, a binder which gels at a temperature higher than a certain temperature, and a plasticizer. Is immersed in hot water at a temperature not lower than the gelation temperature to develop flexibility in the honeycomb molded body, and then the honeycomb molded body is placed on a heat-resistant jig having a curved shape, or heat-resistant having a curved shape. Sandwiched between jigs, 1
Preliminary calcination at 050 to 1150 ° C., then transfer to a heat-resistant jig having a curved shape with a smaller radius of curvature than the heat-resistant jig, and applying a load from the top, further 1200-1
A method of manufacturing a thin plate-shaped ceramic having a curved shape, which comprises firing at 300 ° C. 2. The method for producing a curved thin plate ceramics according to claim 1, wherein the binder is selected from the group consisting of methylcellulose, hydroxypropylmethylcellulose and hydroxypropylcellulose. 3. The method for producing a curved thin plate ceramics according to claim 1, wherein the plasticizer is selected from the group consisting of sorbitan acid ester and polyolefin glycol ether. 4. The inorganic heat resistant material is rehydratable alumina 5 to 30.
wt%, potassium titanate 2 to 7 wt%, fused silica 6
The method for manufacturing a curved thin plate ceramic according to claim 1, wherein the method has a composition of 8 to 93 wt%.