JPS6137228B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an inorganic fiber molded article obtained by forming and drying a slurry or paste-like material consisting of inorganic fibers and colloidal silica, etc. and uniformly curing it, and a method for producing the same. In general, inorganic fiber molded articles obtained by using colloidal silica as a binder in inorganic fibers are widely used as heat-insulating materials for high temperatures because they have excellent heat-resistant insulation properties and thermal shock resistance. However, in this type of molded product, colloidal silica, which is a binder, migrates to the surface of the molded product during drying in the manufacturing process, resulting in a lack of binder inside the molded product, and therefore sufficient mechanical strength cannot be obtained. figure,
There was a drawback that the processability of the molded product and the mechanical strength after processing were significantly reduced. The conventional method for manufacturing such molded bodies is to add inorganic fibers to a dispersion of colloidal silica in water, defibrate them, and disperse them to create a slurry or paste-like product. This is a method of drying and curing the molded material into the shape of the material. However, in this conventional method, a phenomenon occurs in which colloidal silica present inside the molded body migrates from the surface of the molded body to the surface as moisture evaporates from the surface of the molded body during drying, that is, migration occurs. At the end of drying, the gel compound of colloidal silica, which is a binder, gathers near the surface of the molded object, so there is not enough gelled material inside the molded object, and sufficient mechanical strength cannot be obtained. The disadvantage was that the mechanical strength was significantly reduced. In order to overcome the above-mentioned drawbacks, various methods have been studied to prevent migration of colloidal silica, which is a binder, during drying. For example, drying methods include gentle hot air heat transfer drying at low temperatures (43° or
49℃). (Special Publication No. 37-8590) A method of high-frequency heat transfer drying. On the other hand, there is a method of adding a gelling agent to a slurry or paste. (Unexamined Japanese Patent Publication No. 53-27618
(No.) There is also a method of adding a thickener. However, these methods, for example in the above case, reduce productivity due to a significantly long drying time, in the above case, the equipment is very expensive, and it is difficult to apply to objects with complex shapes. There are unresolved problems such as drying and difficulty in controlling the drying process.
In this case, if the stability of colloidal silica in the slurry is reduced, the heat resistance of the molded product is reduced, or if organic substances are used as additives, noxious gas fumes are generated when the molded product is used. This is not a satisfactory method because secondary undesirable phenomena occur. The present invention aims to prevent the migration of colloidal silica inside the molded product during the drying process described above, and the present invention provides a method for drying a molded product that is uniformly cured without causing any of the above-mentioned drawbacks. The purpose is to provide the following. The present invention will be specifically explained below. Inorganic fibers used in the present invention include:
There are ceramic fibers, alumina fibers, zirconia fibers, quartz wool, rock wool, slag wool, glass wool asbestos, etc. Among these, ceramic fibers are most preferred in terms of high heat resistance and cost. Further, colloidal silica used as a binder is used in the form of an aqueous dispersion, and there are no particular restrictions on its concentration. Furthermore, the sodium montmorillonite used for the above purpose of the present invention is a type of montmorillonite, which is a main mineral that constitutes clays such as bentonite and acid clay, and its average particle size is 1 μ × 0.4 μ × The ideal chemical formula with a value of about 0.04μ is Na(Al _5/3 Mg _1/3 )Si ₄ O ₁₀
Among the layered silicate minerals represented by (OH) ₂ ·nH ₂ O, it is a mineral that exhibits characteristic properties such as the largest cation exchange capacity. In other words, sodium montmorillonite exhibits a large swelling power in water and organic solvents, and its dispersion also exhibits large viscosity due to swelling, and as its concentration increases, the thixotropic properties of the liquid increase significantly. be. This property is much higher than that of other clay minerals. The proportion of sodium montmorillonite in the inorganic fiber molded article of the present invention is 0.2 to 20% by weight.
is most preferred. That is, if the proportion of sodium montmorillonite is less than 0.2% by weight, the micration prevention effect will be significantly reduced, and it will be difficult to obtain a molded product having uniform hardness throughout the interior. On the other hand, if it exceeds 20% by weight, the amount of water, which is a dispersion medium for sodium montmorillonite, in the molded product increases, making demolding operations and subsequent handling difficult, and drying shrinkage during drying. big,
The dimensional accuracy of the obtained molded body is significantly reduced. In the production method of the present invention, first, sodium montmorillonite or an aqueous dispersion of sodium montmorillonite is dispersed in water together with colloidal silica, or inorganic fibers are added and defibrated to uniformly disperse the slurry or paste. Add at any time until the product is obtained. in this case,
Both colloidal silica and sodium montmorillonite in the colloidal silica aqueous dispersion, slurry, or slurry-like material are stabilized by a trace amount of alkali, and both particles have the same surface charge, so there is no aggregation due to bonding between them. It maintains long-term positional stability. Then, the slurry or paste is dehydrated and molded, and then dried by a conventional drying method to obtain a molded product. In this case, the colloidal silica in the slurry or paste enhances the thixotropic properties of sodium montmorillonite itself and assumes a gel-like structure after molding or drying the molded product, so it would normally be It was discovered that although sodium montmorillonite has the same charge as sodium montmorillonite and is therefore highly susceptible to migration, it does not cause migration due to being incorporated between sodium montmorillonite particles. Therefore, the molded product obtained by drying does not have extremely low internal hardness like conventional molded products, but exhibits almost uniform hardness throughout the interior. On the other hand, an aqueous dispersion containing colloidal silica and sodium montmorillonite recovered after dehydration molding of a slurry or paste remains in a very stable state as described above, and contains no organic substances at all. Therefore, it has the advantage that it does not rot even if left for a long time and can be used repeatedly over a long period of time. Furthermore, in the process of molding a slurry or paste-like material, it is not only the same as the conventional method, but also superior in terms of workability and production. In this way, the inorganic fiber molded article obtained by the method of the present invention is not only a molded article that is uniformly hardened to the inside, which is the original purpose, but also the constituent materials are all inorganic and are added as a binding agent. Sodium-montmorillonite has excellent heat resistance, so it has sufficient workability and does not lose strength due to processing, and does not contain any organic substances in its constituent materials, so it does not produce harmful gas fumes when heated. There is no damage caused by such occurrences, and the heat resistance is significantly improved, and it has excellent thermal properties at high temperatures. For these reasons, the inorganic fiber molded article of the present invention is optimal as a heat-insulating material that requires post-processing for the purpose of obtaining dimensional accuracy or obtaining a molded article of a desired shape. Used as a heat-retaining and insulating material in fields where the generation of harmful gases and fumes must be avoided in the use of products made of molded bodies as one component or in the working environment, or in fields that require higher heat resistance than conventional products. This is a new and useful inorganic fiber molded product that can Examples of the present invention will be described below. [Example 1] 10% of colloidal silica (particle size 10-20 mμ)
Sodium montmorillonite (chemical composition SiO ₂ 61.18%, Al ₂ O ₃ 22.48%, MgO 3.42
%, Fe ₂ O ₃ 2.09%, CaO 0.54%, Na ₂ O 4.02%,
After adding 12% and 3% by weight of K ₂ O (0.14% Ig loss, 5.98% Ig loss 5.98%) to water and stirring thoroughly, 1% by weight of ceramic fiber to water was added as an inorganic fiber and defibrated. The slurry obtained was subjected to suction dehydration molding (vacuum molding) in a metal mold covered with a wire mesh. Subsequently, it was dried at 150° C. for 10 hours using a conventional hot air dryer to obtain a molded article of 150×150×25 mm ³ .
The bulk specific gravity of the obtained molded product, the surface hardness of the molded product, and the hardness of the internal center were measured. The result is the first
It is shown in A (1-3) of the table. The hardness was measured using a rubber hardness meter (RubbertestertyP-eC). In addition, the same test as above was carried out with chemical composition SiO ₂ 72.99
%, _Al2O3 14.98 _% , MgO0.57%, _{Fe2O3 1.56} %,
CaO1.114%, _Na2O3.54 %, _K2O0.24 %,
It was also carried out for sodium montmorillonite, which has an Igloss of 4.98%. The results are also shown in B (4-6) of Table 1. On the other hand, after vacuum forming, each recovered liquid was allowed to stand for about 5 months, and then the same liquid was used to obtain a molded article under the same conditions as the previous time. The same measurements as the previous time were performed on the obtained molded body again. The results are from 8 to 8 in Table 3.
Shown in 14. In addition, as a molded body for comparison with the molded body obtained by the present invention, a molded body without adding sodium montmorillonite was produced by the same method as above,
The same measurements as above were performed on the obtained molded body. The results are shown in 7 of Table 1.

[Table] The chemical compositions (%) of sodium montmorillonite A and B used here are as shown in Table 2.

【table】

[Example 2]

Similarly to Example 1, sodium montmorillonite (chemical composition; SiO ₂ 61.18%, Al ₂ O ₃ 22.48%, MgO 3.42%,
Fe ₂ O ₃ 2.09%, CaO 0.54%, Na ₂ O 4.02%,
K ₂ O 0.14%, Ig loss 5.98%) to water 1,
After adding 2 to 3% by weight and stirring thoroughly, 1% by weight of rock wool as an inorganic fiber was added to water and defibrated. The slurry obtained was then suction dehydrated (vacuum forming) in a mold with a wire mesh. )did. followed by 150
Dry in a regular hot air dryer at ℃ for 10 hours.
A molded body of 150 x 150 x 25 mm was obtained. The bulk specific gravity of the molded product thus obtained, the surface hardness of the molded product, and the hardness of the internal center were measured. The result is the fourth
Shown in Tables 15 to 17. On the other hand, after vacuum forming, each recovered liquid was allowed to stand for about 5 months, and then the same liquid was used to obtain a molded article under the same conditions as the previous time. The same measurements as the previous one were again carried out on the thus obtained molded article. The results are shown in Table 5, 19-21. In addition, for comparison with the molded product obtained by the present invention, a molded product without the addition of sodium montmorillonite was prepared in the same manner as above, and the same measurements as above were performed on the resulting molded product. Summer. The results are shown in Table 4, 18.

【table】

[Example 3]

Sodium montmorillonite (chemical composition _SiO2 61.18%,
Al ₂ O ₃ 22.48%, MgO 3.42%, Fe ₂ O ₃ 2.09%,
CaO0.54%, _Na2O4.02 %, _K2O0.14 %, Ig
After adding 1% by weight of 5.98% loss to water and stirring thoroughly, 1% by weight of ceramic fiber to water was added as an inorganic fiber, and the resulting slurry was made into a metal with wire mesh. Suction dehydration molding (vacuum molding) was performed in a mold. Subsequently, it was dried at 150° C. for 15 hours using a conventional hot air dryer to obtain a molded article of 200×200×20 mm. In addition, the chemical composition can be determined using the same method as above.
_SiO2 72.99%, _{Al2O3 14.98} %, MgO0.57%,
Fe ₂ O ₃ 1.56%, CaO 1.14%, Na ₂ O 3.54%,
A similar molded body was also produced with the addition of sodium montmorillonite with K ₂ O of 0.24% and Ig loss of 4.98%. The two types of molded bodies obtained in this way were
They were cut into pieces of 100 x 20 mm and subjected to a test to measure the amount of softening when heated under load. The test method for measuring the amount of softening by heating under load is as follows. A test piece measuring 150 x 100 x 20 mm was set on a span support (span length 120 mm), and a load with a bottom surface of 45 x 100 mm was placed parallel to the span at the center of the test piece, and a load of 0.1 Kg/cm ² was applied to the test piece. After setting the measuring rod so that the load is applied, place the measuring rod vertically on the top of the load. The test piece set in this way was heated at a certain rate (room temperature to 1000°C, 3.5°C/mm, 1.5°C above 1000°C).
℃/min) and at the same time measure the vertical change of the tip of the measuring rod. The results are shown in and in the drawings. In addition, for comparison with the molded product obtained from the present invention, a molded product without adding sodium montmorillonite was prepared in the same manner as above, and the same measurements as above were performed on the obtained molded product. Summer. The results are shown in the figure. The bulk specific gravity and montmorillonite chemical composition of the test pieces in the above drawings are shown in Table 6.

[Example 4]

Sodium montmorillonite (chemical composition SiO ₂ 61.18%,
Al ₂ O ₃ 22.48%, MgO 3.42%, Fe ₂ O ₃ 2.09%,
CaO0.54%, _Na2O4.02 %, _K2O0.14 %, Ig
After adding 2, 4, and 6% by weight of (loss5.98%) to water and stirring thoroughly, ceramic fibers were added as inorganic fibers at 10wt% to water, defibrated, and the resulting paste was vacuum-sucked. After press-molding, it was dried at 150° C. for 15 hours in a conventional hot air dryer to obtain a molded product of 150×150×40 mm. The bulk specific gravity of the molded product thus obtained, the surface hardness of the molded product, and the hardness of the internal center were measured. The results are shown in Table 7, 23-25. In addition, for comparison with the molded product obtained by the present invention, a molded product without the addition of sodium montmorillonite was prepared in the same manner as above, and the same measurements as above were performed on the obtained molded product. Ta. The results are also shown in Table 7, 26.

[Table] It is clear from Table 7 above that by adding sodium montmorillonite, a molded article having substantially uniform hardness can be obtained. Further, the obtained molded bodies were processed into various shapes, but all of the molded bodies to which sodium-montmorillonite was added did not deteriorate in handling strength or mechanical strength. As is clear from the above results, the present invention provides a uniformly cured inorganic fiber molded article that does not cause migration and a method for producing the same.
It is extremely useful in this field.

[Brief explanation of the drawing]

The drawing is a graph showing the results of a heat-under-load softening amount measurement test of a test piece of an inorganic fiber molded article of the present invention.

Claims (1)

[Scope of Claims] 1. An inorganic fiber molded article obtained by molding and drying a water additive of a mixture containing inorganic fibers, colloidal silica, and sodium montmorillonite as main components and uniformly curing it. 2. The inorganic fiber molded article according to claim 1, wherein the inorganic fiber is a ceramic fiber containing silica and alumina as main components. 3. The inorganic fiber molded article according to claim 1, which contains the sodium montmorillonite in a weight percentage of 0.2 to 20%. 4 Sodium montmorillonite is added as a binding agent to a slurry or paste made by adding water to a mixture mainly composed of inorganic fibers and colloidal silica, and the mixture is molded and dried to form a colloidal material when dried. A method for producing an inorganic fiber molded article, characterized by preventing migration of silica and uniformly curing the molded article. 5. Claim 4, characterized in that the forming and drying step is a forming method using vacuum forming or press forming, and the drying method is a hot air heat transfer drying method or a radiation heat transfer drying method. A method for producing an inorganic fiber molded article.