JPH05285929A - Method for drying hollow molded article - Google Patents

Abstract

PURPOSE:To prevent the cracking of a hollow molded article at the time of drying by molding the hollow molded article composed of an inorg. powder before forcibly passing air through the hollow part of the molded article. CONSTITUTION:A hollow molded article is a molded article having a hollow part such as a tubular article, a honeycomb article or a foam article having open cells and one opened only at a single end thereof may be adapted but one opened at both ends thereof, especially, a honeycomb article is effective. After this molded article composed of an inorg. powder is molded, air is forcibly passed through the hollow part of the molded article. At this time, it is pref. to pass air only through the inner wall of the molded article. The drying of the molded article may be performed by this method until the dried molded article is obtained but this method is adapted until initial shrinkage due to drying is completed and, thereafter, a usual drying method such as high temp. standing drying or room temp. natural drying is used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel method for drying a hollow molded article of inorganic powder.

[0002]

2. Description of the Related Art At present, hollow molded articles such as ceramics are used for various purposes. For example, ceramic honeycomb molded articles are used in various applications such as catalyst carriers and filters. Further, the tubular ceramics molded product is used for applications such as a tube for a thermocouple and a protection tube for a heating element.

A hollow molded article of inorganic powder such as ceramics or activated carbon is kneaded or dispersed by adding water to a raw material, then molded and dried, and sintered as required to obtain a product. ing.

In the case of a hollow molded article, in this drying step, when it is dried at room temperature or in a dryer, the surface of the inner wall of the molded article is compared with the evaporation rate of water from the surface of the outer wall of the molded article. The evaporation of water from the mold was slow, and the drying speed was imbalanced between the outer wall and the inside of the molded product, causing cracking.

Therefore, when drying a hollow molded article which is susceptible to damage such as cracks, the moisture is slowly evaporated at a low temperature, or the molded article is covered with vinyl or the like to control the evaporation of the moisture and dry it. Had to be done.

There is also a method of drying under high temperature and high humidity in order to suppress the rapid drying at the initial stage of drying (Encyclopedia of New Material Forming and Processing, p. (Published by Industrial Research Institute Material Information Center).

However, even using this method, it was not possible to obtain a dry molded product with few cracks. Moreover, the drying time becomes very long.

Further, a method has been proposed in which a heat-coagulable polysaccharide is blended with an inorganic powder, a molded product is heated to coagulate the heat-coagulable polysaccharide, and then this is dried (Japanese Patent Laid-open No. 3- 1
31562). However, in this method, since the thermocoagulable polysaccharide is coagulated, a step of suppressing evaporation of water is required.

The conventional method as described above has not yet been able to sufficiently prevent cracking of the dried molded product.

Further, in such a conventional method, a dry molded product cannot be produced unless conditions for the drying process are set to be quite strict. For this reason, workability and production efficiency have deteriorated, and depending on the obtained dry-molded product, there have been cases where sufficient drying is impossible even with sufficient care.

Further, despite the disadvantage in the characteristics of the molded product, it is necessary to use many binders so as not to be cracked, which is disadvantageous.

[0012]

SUMMARY OF THE INVENTION It has been desired to develop a method for drying a hollow molded article of an inorganic powder which can surely obtain a completely dry molded article without cracks and the like by a simple method.

[0013]

Means for Solving the Problems The present inventor has made earnest studies on a hollow molded article of inorganic powder, and after molding the inorganic powder into a hollow shape, air is forced into the voids of the molded article. After venting, the inventors obtained the finding that the dried molded product is less likely to suffer damage such as cracks even after being subjected to rapid drying at a high temperature thereafter, and further studies were conducted to complete the present invention.

That is, the present invention relates to a method for drying an inorganic powder molded article, which comprises forming a hollow molded article of the inorganic powder and then forcibly ventilating the hollow portion of the molded article.

The hollow molded article in the present invention refers to a molded article having a hollow portion such as a tubular molded article, a honeycomb shaped article, and a foam having a communicating hole. Further, both ends of the molded product may be open, or only one end face may be open. In particular, the drying method of the present invention is suitable for the case where both ends are open. Especially, the open area ratio is 20
It is particularly effective for ˜95% honeycomb-shaped molded products. The shape of the honeycomb holes may be any shape such as a polygon such as a triangle or a square or a circle.

Further, the hollow portion means a void portion in the tube of the tubular molded product, a void portion of the cell hole of the honeycomb molded product, and the like.

If the raw material of the molded product is an inorganic powder,
Although not particularly limited, industrial ceramic powder, activated carbon, etc. are mainly targeted.

Industrial ceramic powders include silica, alumina, titania, magnesia, ferrite, synthetic cordierite, zirconia, zirconium oxide, mullite, spinel, barium titanate, oxides of zeolite, silicon carbide, boron carbide, etc. Carbide, nitride such as silicon nitride, boron nitride, aluminum nitride, boride such as zirconium boride and titanium boride, kaolin, talc, sepiolite, hydroxyapatite and the like.

The drying method of the present invention is particularly effective for drying a molded product having a fast drying property such as zeolite.

Such a zeolite is not particularly limited and may be a natural zeolite or a synthetic zeolite. Further, two or more kinds may be mixed and used. Examples of such natural zeolite include chabazite type, natural mordenite type, clinoptilolite type and erionite type. A as a synthetic zeolite
Type (Mizusawa Chemical Industry Co., Ltd. Silton B ^TM, Mizukashibusu 4A ^TM, etc.), X-type (Mizusawa Chemical Industry Co., Ltd. Mizukashibusu X ^TM, etc.), Y type (Mizusawa Chemical Industry Co., Ltd. Mizukashibusu Y
^TM, etc.), synthetic mordenite type, and high silica type (MFI type, etc.). Furthermore, Si /
Those having different Al atomic ratios and structures, and zeolites composed of other elements can also be used.

Further, as the binder to be added when adjusting the molding compound of the inorganic powder, those usually used may be used.

For example, synthetic resins such as polyvinyl alcohol, polyvinyl butyral, polyethylenegunicol and cellulose derivatives, natural polysaccharides such as alginic acid, gum arabic, dextrin, curdlan and paramylon, and inorganic substances such as clay and kaolin are used. To be done.

These binders are usually used in an amount of 1 to 50 parts by weight based on the inorganic powder.

For example, when zeolite is formed into a honeycomb shape, when the amount of the binder added is more than 30% by weight, cracking is relatively small even by the ordinary drying method.
When it is up to 30% by weight, cracks are likely to occur in the drying process.

Usually, a binder and a suitable amount of water are added to the above-mentioned inorganic powder to prepare a compound of the inorganic powder, which is then formed into a desired shape such as a honeycomb shape or a tubular shape.

The molding method is not particularly limited, but when water is used for preparing the compound, extrusion molding, injection molding or the like can be applied as the molding method.

By subjecting the molded product thus obtained to the drying method of the present invention, a dry molded product without cracks can be obtained. Specifically, after molding the inorganic powder molded product, forced ventilation may be provided to the hollow portion of the hollow molded product. This step promotes the drying of the inside (inner wall) of the molded product,
The difference in the drying speed between the outer surface of the molded article and the inside is reduced, and the distortion of the molded article that occurs in the initial stage of drying is suppressed and the strength of the molded article is maintained. This initial drying greatly affects the strength of the molded product, and the molded product thus obtained is less likely to suffer damage such as cracks even in the subsequent drying step.

The method of forced ventilation is not particularly limited. Specifically, in a dryer with a powerful fan,
A method of placing the hollow molded article so that the direction of the wind and the direction of the holes are the same, a method of placing the hollow molded article in the air outlet of a dryer or a compressor, and the like can be used. Also,
A method of sucking the air existing in the hollow portion with a vacuum pump or the like can also be applied.

At this time, the hollow molded article is controlled by squeezing the air outlet to control ventilation or by wrapping only the outer wall portion of the hollow molded article with a synthetic resin film or a non-woven fabric moistened with water. It is preferable to ventilate only the internal cell portion (inner wall). According to this method, a dry molded product without cracks can be obtained in a shorter time than the method of ventilating and drying the entire hollow molded product.

The air to be aerated may be normal air, warm air, or hot air. Air under normal workplace conditions, such as room temperature and normal humidity, can be used.
Specifically, the temperature is higher than 0 ° C and 150 ° C or lower, preferably 5 to 120 ° C, and the relative humidity (RH) is 80% or lower. More preferably, it is 70% or less.

The amount of air flow only needs to be such that air passes through the pores of the molded product, and is appropriately determined depending on the shape and size of the dried molded product. For example, in the case where both ends of the molded product are open, air may pass from one open end to the other open end. Further, when only one end face is opened, the air in the hollow part of the molded article can be circulated by a method of blowing compressed air from the opening end or a method of sucking air existing in the hollow part. Good.

The molded article may be dried completely by the drying method of the present invention until a dried molded article is obtained.
It is not necessary to completely dry, and it may be until the initial shrinkage of the molded product due to drying is completed. Generally, it is sufficient to carry out initial drying until the end of the constant rate drying period. Since this initial shrinkage differs depending on the type of the inorganic powder, the aeration time may be appropriately determined according to the raw material used.

When the aeration is terminated at this initial drying degree, in order to obtain a completely dry molded product after the initial drying,
A normal drying method such as static drying at high temperature or natural drying at room temperature may be used. For example, immediately after the initial drying, 115
The molded product can be dried in 1 to 2 hours when it is placed in a dryer at ℃.

Further, after drying the molded product, if desired, it can be sintered to obtain a desired inorganic powder sintered product.

[0035]

According to the present invention, when a hollow molded article is dried, air can be ventilated through the inner wall of the molded article to easily prevent cracking of the molded article during drying.

By this method, it is possible to efficiently and easily manufacture a honeycomb-shaped molded article which has been conventionally considered to be difficult and time-consuming especially in the drying step.

[0037]

【Example】

[Production Example-1] Production of Zeolite Honeycomb Molded Product 700 g (solid content) of high silica synthetic zeolite powder (Mizuka Sieves EX-12 manufactured by Mizusawa Chemical Industry Co., Ltd.)
2 ^TM ), 50 g (solid content) of bentonite powder (Benclay ^TM manufactured by Mizusawa Chemical Industry Co., Ltd.), 50 g of glass fiber (Nippon Sheet Glass Co., Ltd., Micrograss Chopped Strand ^TM RES015) and 200 g (solid). Kibushi clay (solid content) (made by Maruo Calcium) was added.
Further, 12.5 g of curdlan (manufactured by Takeda Pharmaceutical Co., Ltd.) and 31.3 g of hydroxypropylmethylcellulose (viscosity of 2% by weight aqueous solution at 20 ° C .: about 28,000 centipoise) and 6.2 g of Polyethylene glycol (manufactured by Sanyo Kasei Co., Ltd., Macrogol 6000 ^™ ) was added, and this mixture was dry-mixed for about 1 hour using a tabletop twin-screw kneader.

Next, distilled water was added to this mixture so that the total amount of water was 4.
Add to 40 g and under reduced pressure (about 100-7
The mixture was kneaded for about 1 hour. In this kneading,
Cold water at 10 ° C. was circulated in the jacket of the kneading machine to cool the kneaded product.

The kneaded material thus obtained was placed in a polyethylene bag and aged at room temperature to 40 ° C. for about 3 to 5 days. Next, an extruder (DE-35 manufactured by Honda Iron Works Co., Ltd.)
Mold) and kneaded under reduced pressure to obtain a kneaded solid composition for zeolite molding.

Next, a honeycomb molding die was mounted on the above-mentioned extrusion molding machine, and the kneading composition was vertically prepared by using this.
It was extruded into a prismatic honeycomb shape of 0 mm × width 30 mm and 300 cells / square inch.

Next, this was cut into a length of 40 mm to obtain a honeycomb-shaped molded product.

[Example-1] In the cell holes of the zeolite honeycomb molded article obtained in Production Example-1, 2.5 kg / cm ² ,
RH: 0%, air at 24 ° C. was blown for 30 seconds. This compressed air was squeezed with a nozzle so as to contact only the inner wall of the cell hole and not the outer wall of the honeycomb.

Then, the formed honeycomb article was heated at 24 ° C.
After subjected to natural drying for 24 hours under the condition of RH: 43%, a dried molded product was obtained.

Five dry-molded products were prepared in the same manner as described above. The cracking characteristics are shown in [Table 1].

[Example-2] In the cell holes of the zeolite honeycomb molded article obtained in Production Example-1, 2.5 kg / cm ² ,
RH: 0%, air at 24 ° C. was blown for 30 seconds. Ventilation by this compressed air was performed by narrowing the nozzle so as to contact only the inner wall of the cell hole and not the outer wall of the honeycomb.

Then, the formed honeycomb article was treated at 115 ° C.
R.H .: It heat-dried for 2 hours on condition of 1%, and the dry molding was obtained.

Five dry molded products were prepared in the same manner as above. The cracking characteristics are shown in [Table 1].

[Example-3] RH: 3%, 80 ° C was added to the cell holes of the zeolite honeycomb molded article obtained in Production Example-1.
Hot air was blown for 120 seconds. The ventilation by the warm air was performed so as to contact the cell holes and the outer wall of the honeycomb.

Then, the honeycomb formed article was heated at 115 ° C.
R.H .: It heat-dried for 2 hours on condition of 1%, and the dry molding was obtained.

Five dry-molded products were prepared in the same manner as above. The cracking characteristics are shown in [Table 1].

[Example-4] RH: 3%, 80 ° C was added to the cell holes of the zeolite honeycomb molded article obtained in Production Example-1.
Hot air was blown for 30 seconds. At this time, the opening end of the honeycomb formed article was not blocked, and only the outer wall of the formed article was wrapped with a synthetic resin film so that the warm air was mainly in contact with the inner wall of the cell hole.

Then, the honeycomb molded product was subjected to heat drying for 2 hours under the conditions of 115 ° C. and RH: 1% while being wrapped, to obtain a dried molded product.

Five dry molded products were prepared in the same manner as above. The cracking characteristics are shown in [Table 1].

[Example-5] RH: 3%, 80 ° C was added to the cell pores of the zeolite honeycomb molded article obtained in Production Example-1.
Hot air was blown for 30 seconds. Ventilation with this warm air was performed so that the nozzle was narrowed so that only the inner wall of the cell hole was in contact with it, and not the outer wall of the honeycomb.

Then, the honeycomb formed article was heated at 115 ° C.
R.H .: It heat-dried for 2 hours on condition of 1%, and the dry molding was obtained.

Five dry molded products were prepared in the same manner as above. The cracking characteristics are shown in [Table 1].

[Example-6] The dry-molded products obtained in Examples 1-5 were prepared by using an electric furnace (manufactured by Motoyama Co., SUPER BURN SB-20).
When fired at 700 ° C. for 2 hours in a 25D type), no new crack or the like was generated, and a good fired product was obtained.

[Comparative Example-1] The honeycomb molded article obtained in Production Example-1 was air-dried for 24 hours at 24 ° C and RH: 43% to obtain a dried molded article. Obtained.

Five dry-molded products were prepared in the same manner as above. The cracking characteristics are shown in [Table 1].

[Comparative Example-2] The honeycomb molded article obtained in Production Example-1 was heated and dried for 2 hours at 115 ° C and RH: 1% to obtain a dried molded article. Obtained.

Five dry molded products were prepared in the same manner as above. The cracking characteristics are shown in [Table 1].

[Comparative Example-3] The open ends of the honeycomb molded article obtained in Production Example-1 were not covered, and the outer wall was wrapped with a synthetic resin film. It was subjected to heat drying for 2 hours under the conditions to obtain a dried molded product.

Five dry molded products were prepared in the same manner as above. The cracking characteristics are shown in [Table 1].

[0064]

[Table 1]

[Production Example-2] Production of Alumina Honeycomb Molded Product 2,500 g (solid content) of alumina (Showa Denko KK)
Ltd., AL-160SG-4) 125 grams of ceramic molding binder (Takeda Chemical Industries, Ltd., Biopori ^TM P-
1) was added, and this mixture was mixed with a table-top twin-screw kneader for about 1 hour
Dry mixed.

Then, to this mixture was added distilled water so as to give 500 g, and the pressure was reduced (about 100 to 700 mmH).
k) was kneaded for about 1 hour. In this kneading, cold water at 10 ° C. was circulated in the jacket of the kneader to cool the kneaded product.

The kneaded material thus obtained was put into a polyethylene bag and aged at room temperature to 40 ° C. for about 3 to 5 days. Next, this is an extruder (DE-35 made by Honda Iron Works Co., Ltd.
Mold) and kneaded under reduced pressure to obtain a kneaded solid composition for alumina molding.

Next, a honeycomb molding die was mounted on the extrusion molding machine, and using this, the kneading composition was formed into a prismatic honeycomb having a vertical length of 30 mm × a width of 30 mm and a number of cells of 300 cells / square inch. It was extruded into a shape.

Next, this was cut into a length of 40 mm to obtain a honeycomb-shaped molded product.

[Example-7] Warm air of RH: 3%, 80 ° C was blown into the cell holes of the alumina honeycomb molded article obtained in Production Example-2 for 30 seconds.

Thereafter, the honeycomb formed article was heated at 115 ° C.
R.H .: It heat-dried for 2 hours on condition of 1%, and the dry molding was obtained.

Five dry-molded products were prepared in the same manner as above. The cracking characteristics are shown in [Table 2].

[Example-8] An electric furnace (SUPER BURN SB-2025D manufactured by Motoyama Co., Ltd.) was used for the dry-molded product obtained in Example-7.
When fired at 1,600 ° C. for 2 hours in the mold ( ^TM ), no new crack or the like was generated, and a good fired product was obtained.

[Comparative Example-4] The honeycomb molded article obtained in Production Example-2 was heated and dried for 2 hours under the conditions of 115 ° C and RH: 1% to obtain a dried molded article. Obtained.

Five dry molded products were prepared in the same manner as above. The cracking characteristics are shown in [Table 2].

[0076]

[Table 2]

Claims (2)

[Claims] 1. A method for drying an inorganic powder molded article, comprising forming a hollow molded article of the inorganic powder and then forcibly ventilating the hollow part of the molded article. 2. The drying method according to claim 1, wherein the hollow molded article is a honeycomb molded article.