JPH0253385B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing an inorganic fiber molded article, and more particularly, to a method for producing an inorganic fiber molded article with a high yield of colloidal silica. In general, inorganic fiber molded products obtained by using colloidal silica aqueous solution as a binder for inorganic fibers have excellent heat resistance, heat insulation properties, and thermal shock resistance, and are therefore widely used as heat-insulating materials for high temperatures. . Conventionally, such inorganic fiber molded articles have been produced by placing inorganic fibers in an aqueous solution of colloidal silica dispersed in water, defibrating and dispersing them, forming a slurry or paste into a predetermined shape, and then drying. It is manufactured by a hardening method. However, in such conventional methods, a phenomenon known as migration occurs, in which colloidal silica components migrate from the half-dried molded product during drying and collect only in the surface layer. After drying, only the surface layer hardens, while the inner layer remains soft. If this happens, only the solid formations will be obtained.
Therefore, the above-mentioned conventional methods leave many problems in the processability of the molded product and its handling during processing. Therefore, in order to solve the above-mentioned problems, various studies have been made to prevent migration of colloidal silica, which is a binder. For example, in the invention described in Japanese Patent Publication No. 37-8590, gentle hot air drying is performed at a low temperature of 43 to 49°C, but this method requires a long time for drying and is not preferred in terms of the process. Furthermore, in the invention described in JP-A-53-27618, a molded body is made by adding calcium silicate or magnesium silicate as a hardening agent for colloidal silica, and the colloidal silica and hardening agent are reacted during firing. Although the migration of colloidal silica is suppressed, this method has the disadvantage that the yield of colloidal silica is poor and stability is insufficient when reusing the slurry liquid. Furthermore, in the invention described in JP-A No. 58-104059, aluminum sulfate is added as a hardening agent for colloidal silica, and then high molecular weight polyethylene oxide is added to fix the colloidal silica to the inorganic fibers. However, this method has many drawbacks such as poor yield of colloidal silica and poor filterability of the slurry liquid. The present invention improves the drawbacks of the prior art described above,
The present invention relates to a method of uniformly and firmly bonding colloidal silica to inorganic fibers to improve the yield of colloidal silica and to obtain an inorganic molded body suitable for high-temperature applications. That is, the present invention adds a coagulant to a slurry liquid made by dispersing inorganic fibers and colloidal silica in a dispersion medium, and quickly adjusts the pH of the slurry liquid.
4.5 or less to produce colloidal silica condensate, then preferably the pH of the slurry liquid is 4.5 to 4.5.
8.5, add a polymer coagulant to the slurry liquid to fix the colloidal silica coagulant to the inorganic fibers, and then mold and process the slurry liquid. The present invention provides a method for producing a molded body, which may be used as a product in an undried state, or a method of obtaining a molded body by drying or firing to remove flammable substances. Furthermore, the present invention also includes a method for producing a molded article, in which a required amount of filler such as sand, clay, mineral powder, etc. is added to the slurry liquid as necessary, and the slurry liquid is molded and processed. It is. According to the method of the present invention, the slurry liquid for inorganic fiber molded bodies has good filtration properties during molding and processing, the yield of colloidal silica is significantly improved, and migration does not occur during drying of the obtained molded bodies. It is possible to obtain a molded product with high strength and high hardness. The present invention will be specifically explained below. Inorganic fibers used in the present invention include:
Ceramic fiber, alumina fiber, zirconia fiber, quartz wool, rock wool, crag wool, glass wool, asbestos,
Titanate fibers, boron carbide fibers, silicon carbide fibers, silicon nitride fibers, various whiskers, etc. can be selected from the group consisting of each of these fibers and mixtures thereof, but depending on the heat resistance and economic efficiency of the fibers, Ceramic fiber is the most suitable for this purpose. In addition, colloidal silica (commonly known as silica sol) used in the present invention is an aqueous colloidal dispersion solution of SiO ₂ (silica), and is used in various ways, such as neutralization of sodium silicate and ion exchange treatment of sodium silicate. Products include Snowtex (Nissan Chemical Products), Adelite (Asahi Denka Products), and Rudotsux (DuPont products).
Usually, the size of colloid particles is 5 to 100 mμ,
A SiO ₂ (silica) concentration of 20 to 50% by weight is used. Water is suitable as a dispersion medium necessary to make a slurry of inorganic fibers, colloidal silica, and a filler added as necessary, but methanol,
Ethanol, ethylene glycol, diethylene glycol, propylene glycol, glycerin,
and mixtures thereof can also be used alone or as a mixture with water. The amount of dispersion medium is adjusted depending on the amount of inorganic fibers and the amount of colloidal silica used, but it is necessary to have at least an amount that sufficiently disperses the fibers, for example, the weight ratio of the dispersion medium and inorganic fibers is The ratio is 100:0.1 to 10:1, more preferably 100:1 to 100:4. In the present invention, the quantitative relationship between colloidal silica used as a binder and inorganic fibers is preferably such that SiO ₂ in the colloidal silica is smaller than the inorganic fibers.
The solid content is in a weight ratio of 100:1 to 100:30, more preferably 100:3 to 100:20; if it is less than this, the strength of the intended molded product is likely to decrease, or it is too much. filterability tends to be difficult. Coagulants used in the present invention include acids (e.g., hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, organic acids), salts (e.g., chlorides, sulfates, nitrates), alumina sol, and sodium aluminate. Particularly preferred are acids, aluminum sulfate, aluminum chloride, polyaluminum chloride, and alumina sol. The function of the coagulant here is to adhere to the surface of colloidal silica and coagulate colloidal silica particles, and in order to complete the coagulation more quickly, the slurry liquid is
It is necessary for the coagulant to work under conditions of pH 4.5 or lower. This is because if the pH exceeds 4.5, not only will the coagulant's coagulating effect not be fully demonstrated, but if an acidic salt such as aluminum chloride is used as a coagulant, much of the aluminum chloride will turn into aluminum hydroxide and will not be used as a coagulant. This is because it eliminates the function of A suitable method for lowering the pH of the slurry liquid to 4.5 or less is to use a mineral acid, but if the alkalinity of the slurry liquid is low, an acid salt can be used as a coagulant instead. In any case, the conditions for the reaction between colloidal silica and coagulant are that the pH of the slurry liquid is 4.5 or less,
More preferably, the pH range is from 3 to 4.5.
The mixing ratio of colloidal silica and coagulant is preferably 100:0.5 to 10:2 in solid weight ratio. As for the reaction time, stirring for about 1 to 10 minutes at room temperature is sufficient. Next, a polymer flocculant is added, but at this time, it is preferable to adjust the pH of the slurry liquid to 4.5 to 4.5 again.
It is better to revert to 8.5. This makes the colloidal silica coagulate produced by the reaction between colloidal silica and coagulant more stable, improves filterability, and further improves the yield of colloidal silica. In this case, if the pH is set to 8.5 or higher, re-dissociation of colloidal silica coagulum occurs, which is not preferable. The pH of the slurry liquid is from 4.5 or less to 4.5
~8.5 Metal hydroxides and alkaline salts are suitable as the chemical solution, but for example, caustic soda,
More preferred are soda carbonate, sodium silicate, alkali silicate, and sodium aluminate. The important point in the present invention is to use a polymeric flocculant to produce a floc of inorganic fibers on which colloidal silica aggregates are fixed. By using this polymer flocculant, the colloidal silica coagulates firmly adhere to the inorganic fibers, resulting in a slurry liquid with good filterability and a good yield of colloidal silica. The polymer flocculant referred to herein is a polymer flocculant generally used in the water treatment field, and is divided into natural polymers and their derivatives and synthetic polymers, depending on the raw materials and manufacturing methods. Examples of natural polymers and their derivatives include starch and its derivatives, cellulose and its derivatives, sodium alginate, protein, konjac, agar, pectic acid, chitozan, and the like. Synthetic polymers are
It is further divided into polymerization type and condensation type. Polymerization types include, for example, modified products of polyacrylic acid, polyacrylamide, maleic acid condensates, and their copolymers, and are generally nonionic, anionic, and cationic. sex is manufactured. The condensed type is, for example, a polycation. Among these, more preferably
A synthetic polymer flocculant with a molecular weight of 100,000 or more is suitable. Commercial products of this polymer flocculant include, for example, Flownac (Kyowa Yushi Products), Diafloc (Diafloc Products), Sumifloc (Sumitomo Chemicals), and Adeka Flocker (Asahi Denka Products).
etc. These polymer flocculants are mixed and stirred with the above-mentioned solvent in advance and used as a solution at a required concentration. Although the amount used varies depending on each flocculant, it is preferably added in the form of a solution of 0.1 to 0.5% by weight to the slurry liquid in the form of a solution of 0.02 to 1.0% by weight. This is because if the amount is less than 0.02% by weight, the effect will not be exhibited very much, and if it is more than 1.0% by weight, there is a risk that the generated flocs will be redispersed. The form of the molded article produced by the present invention is as follows:
Possible materials include paper, board, mat, tube, rod, and block. For example, in the case of manufacturing paper or pods, a slurry liquid (composition slurry) in which colloidal silica aggregates are fixed to inorganic fibers is filtered on a wire mesh, and then water is removed using a compression roller. or remove water by suction dehydration and mold. In the case of other molded bodies, the above composition slurry is filtered to form a cake;
It can be molded into a suitable mold. On the other hand, the filtered filtrate is almost completely transparent, contains almost no active ingredients such as colloidal silica, coagulants, polymer flocculants, and other inorganic fibers, and only contains a small amount of inorganic salts, making it an ideal resource for recycling. Alternatively, direct discharge into rivers is possible. Incidentally, in order to increase the density of the inorganic fiber molded article of the present invention, to further improve heat resistance and heat retention, to improve processing, or to increase the amount, sand or similar materials (for example, silica) may be used. sand, zircon sand, alumina sand, molten glass sand, etc.) Furthermore, even if clay minerals (e.g., kaolin, bentonite, talc, mica, etc.) are added to the slurry liquid in the present invention and molded and dried, the object of the present invention can be achieved. A high-strength, high-hardness inorganic fiber molded article that prevents migration can be obtained, and at the same time, a clean filtrate with a good yield of colloidal silica can be obtained. EXAMPLES Hereinafter, the present invention will be explained in detail based on Examples, but the present invention is not limited to these Examples. Example 1 Colloidal silica (SiO ₂ 30%,
15 g of Na ₂ O (0.03%, particle size: 10 to 20 mμ) and 20 g of ceramic fiber (Japan Asbestos Co., Ltd.; Fine Ceramic Fiber 1300) were added, and a homogeneous slurry liquid was prepared using a mixer. This slurry liquid
The pH was 10.3. Next, 3 g of 20% aluminum sulfate aqueous solution was added to this, and the pH of the slurry liquid was adjusted to 3.8.
And so. After stirring this for 5 minutes, 10%
The pH of the slurry liquid was adjusted to 6.3 by adding NaOH aqueous solution. To this slurry liquid, 1 g of 0.1% aqueous solution of Adeka Flocker (Asahi Denka, 20A-80, anionic) was added to prepare a final slurry liquid. This final slurry liquid was subjected to suction dehydration molding in a metal mold provided with a wire mesh to obtain a molded product. This molded body was heated to 110 to 140℃ for 6
Dry for an hour, and have a diameter of 50 mm and a height as shown in Figure 1a.
A 40 mm cylindrical inorganic fiber molded body 1 was obtained. As shown in FIG. 1b, this inorganic fiber molded body 1 is
It was cut into a test piece 1'. The compressive strength at each measurement point H and M (H is the center point of the top surface, M is the center point of the entire cross section, see Figure 1b) on the test piece 1' was measured using an autograph (manufactured by Shimadzu Corporation, type IS-2000). )
It was measured with The measurement results are shown in Table 1 and Figure 2. For the above measurements, a steel rod with a diameter of 5 mm was used as the compressed metal rod, and the steel rod was lowered at a descending speed of 1 mm/min, and the recording paper was moved at a speed of 20 mm/min. . Furthermore, in Table 1, the compressive strength when the compressed metal bar penetrates 0.2 mm into the test piece 1' is defined as hardness, and the compressive strength when the compressed metal bar penetrates 0.5 mm is defined as strength, and each is expressed in units of Kg/ ^cm2 . . Further, FIG. 2 shows a graph showing the relationship between the compressive strength at measurement point M and the amount of penetration of the compressed metal rod into the test piece. In addition, the filtration rate of the final slurry liquid and the properties of the filtrate were measured. The results are shown in Table-2. Example 2 The amount of colloidal silica was 20g, and the amount of coagulant was 20g.
3g of aluminum chloride, 0.1% of Adeka Flocker 10N-40 (anion) as a polymer flocculant
An inorganic fiber molded article was obtained in the same manner as in Example 1 except that 1 g of the aqueous solution was used, and the same measurements as in Example 1 were performed on this inorganic fiber molded article. The results are shown in Table-1 and Table-2. Example 3 Adeka Flocker 30C-60 as a polymer flocculant
An inorganic fiber molded article was obtained in the same manner as in Example 1 except that 1 g of a 0.1% aqueous solution of (cation) was used, and the same measurements as in Example 1 were performed on this inorganic fiber molded article. The results are shown in Table-1 and Table-2. Example 4 An inorganic fiber reinforced molded body was obtained in the same manner as in Example 1 except that the amount of coagulant added was 2 g and a 0.1% aqueous solution of Adeka Flocker 10N-40 (nonionic) was used as the polymer coagulant. The same measurements as in Example 1 were performed on the inorganic fiber molded article. Table the results.
1. Shown in Table-2. Example 5 An inorganic fiber molded article was obtained in the same manner as in Example 1, except that 4 g of polyaluminum chloride aqueous solution (Sumitomo Aluminum Products, PAC, 10% Al ₂ O ₃ product) was used as a coagulant. The same measurements as in Example 1 were performed on the body. The results are shown in Table-1 and Table-2. Example 6 A molded article was obtained in the same manner as in Example 1, except that the pH was not adjusted. The results are shown in Table-1 and Table-2. Comparative Examples 1, 2, 3 In Example 1, Comparative Example 1 is a case where no coagulant is added, PH adjustment, or polymer flocculant is added, and a case where PH adjustment or polymer flocculant is not added is called Comparative Example 1. Comparative Example 2 was defined as Comparative Example 2, and Comparative Example 3 was defined as Comparative Example 3 in which no polymer flocculant was added. Inorganic fiber molded bodies were obtained in the same manner as in Example 1, and the same measurements as in Example 1 were performed on each of these inorganic fiber molded bodies. The results are shown in Table-1 and Table-2.

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[Table] As is clear from the results shown in Table 1, Table 2, and Figure 2, the inorganic fiber molded product obtained by the method of the present invention has high strength and high hardness without migration. In addition, it can be seen that the yield of colloidal silica is high and the filtration property is excellent during its production, making it an extremely excellent product in terms of the production process.

[Brief explanation of drawings]

FIG. 1a is a perspective view of an inorganic fiber molded product obtained in an example of the present invention, FIG. 1b is a perspective view of a test piece formed by cutting the inorganic fiber molded product, and FIG. is a graph showing the relationship between the compressive strength at measurement point M and the amount of penetration of the compressed metal rod into the test piece.

Claims (1)

[Claims] 1. A coagulant is added to a slurry liquid in which inorganic fibers and colloidal silica are dispersed in a dispersion medium, and the pH of the slurry liquid is immediately adjusted to 4.5 or less to produce a colloidal silica coagulate, and then a high 1. A method for producing an inorganic fiber molded article, which comprises adding a molecular flocculant to fix the colloidal silica coagulate to inorganic fibers, and then molding and processing the slurry liquid.