JP4539850B2 - Method for producing silica molded body and method for producing silica glass product for sintering the silica molded body - Google Patents

Description

  The present invention relates to a method for producing a silica molded body and a method for producing a silica glass product by sintering the silica molded body.

  Conventionally, as a simple method for producing a silica glass product, there are a press molding method, a cast molding method, an injection molding method, and the like. However, the press molding method has a drawback that a product having a large shape or a complicated shape cannot be produced. Further, the casting molding method has a drawback that a large amount of an organic binder is blended in order to ensure the fluidity of the casting raw material, and impurities are mixed in to cause high purity products. Furthermore, in the injection molding method, as shown in Patent Document 1, it is difficult to completely remove the organic binder from the molded product because the organic binder is blended in a large amount of 10 to 70% by mass with respect to the silica raw material. In addition, high-purity silica glass products cannot be produced, and the silica glass product is deformed or cracked due to the organic binder.

On the other hand, the raw material is ceramic powder. Utilizing the thermal gelation properties of cellulose ether, cellulose ether is mixed with the ceramic slurry above its gelation temperature and poured into a mold cooled to below the gelation temperature. A manufacturing method has been proposed in which solidification is performed after the solidification (Patent Document 2). However, the production method has a drawback that cellulose ether is not dissolved but is mixed into the molded body, vaporized by sintering, and bubbles are mixed therein.
JP-A-4-349130 JP 2000-280210 A

    In view of the current situation, the present inventors have conducted intensive research. As a result, the slurry containing silica fine powder and water was heated to a temperature not lower than the gelation temperature of the cellulose derivative aqueous solution and not higher than 100 ° C., and then the cellulose derivative powder was added and dispersed. And after cooling it to 10 ° C. or less, it is injected into a mold heated to a temperature not lower than the gelation temperature of the cellulose derivative aqueous solution and not higher than 150 ° C., so that the silica glass product having a complicated shape can be used even when using a small amount of organic binder. However, the present invention has been completed by finding that it can be manufactured accurately and inexpensively without bubbles being mixed therein. That is,

  An object of this invention is to provide the method of manufacturing the complicated shaped silica molded object accurately and cheaply.

  It is another object of the present invention to provide a method for producing a silica glass product having a complicated shape and free of bubbles in the silica glass product.

  The present invention that achieves the above object is to add and disperse the cellulose derivative powder to a slurry containing silica fine powder heated to 100 ° C or lower and a gelling temperature of the cellulose derivative aqueous solution, and then cool to 10 ° C or lower. The present invention relates to a method for producing a silica molded product, which is injected into a mold heated to a gelling temperature of a cellulose derivative aqueous solution or higher and 150 ° C. or lower, and a method for producing a silica glass product for sintering the silica molded product.

  Examples of the silica fine powder used in the present invention include natural silica fine powder and synthetic silica fine powder. The particle size of the fine powder is preferably in the range of 0.1 to 20 μm. The shape is preferably spherical. Injection can be performed satisfactorily because the fine powder is spherical. In particular, synthetic silica fine powder has many hydrophilic silanol groups on its surface, and when mixed with water, the silanol groups on the surface of the silica fine powder form hydrogen bonds with each other, and the silica fine powder forms a three-dimensional network structure. In addition, there is an advantage that a molded body having a high strength can be obtained by hydrogen bonding with an unsubstituted hydroxyl group of the cellulose derivative to be blended, and the subsequent steps can be carried out smoothly. When the particle size of the silica fine powder is less than 0.1 μm, the viscosity becomes high and it becomes difficult to add and mix the cellulose derivative powder. On the other hand, when the particle diameter exceeds 20 μm, the surface of the injection molding machine or the mold is worn, and the worn debris is mixed into the silica molded body and contaminated, which is not preferable. In particular, the content of alkali metals, alkaline earth metals, and iron that cause crystallization is preferably 50 ppm or less.

  Examples of the cellulose derivative powder include methylcellulose, hydroxypropylmethylcellulose, and hydroxymethylcellulose. Particularly, methylcellulose having an aqueous solution of 30,000 mPa · s or more at 2% by mass is preferable. By using the methylcellulose, good moldability can be maintained even if the amount of the cellulose derivative powder mixed with the silica fine powder is reduced. The addition amount of the cellulose derivative powder is 0.1 to 10% by mass, preferably 0.1 to 5% by mass with respect to the solid content of the silica fine powder. If the addition amount is less than 0.1% by mass, sufficient moldability cannot be maintained. On the other hand, if it exceeds 10% by mass, the shrinkage rate during sintering increases, and deformation or cracks occur in the product. The aqueous solution viscosity of the cellulose derivative powder was measured according to the Ubbelohde viscometer No. 5 is a value measured as a 2 mass% aqueous solution viscosity at 20 ° C. The mixed slurry containing cellulose derivative powder further comprises, if necessary, fatty acids such as stearic acid, water-soluble polyhydric alcohols such as ethylene glycol, glycerin, and sorbitol, and adducts such as propylene oxide, ethylene oxide, and fatty acids. It is better to add a plasticizer to improve fluidity.

  In the production method of the present invention, as described above, the silica glass fine powder and the slurry containing water are heated to a temperature not lower than the gelation temperature of the cellulose derivative aqueous solution and not higher than 100 ° C., and while stirring little by little so as not to aggregate the cellulose derivative powder. It is a method for producing a silica molded body that is added, mixed, cooled, poured into an injection cylinder or cooled in an injection cylinder, and injected into a mold heated above the gelation temperature of an aqueous cellulose derivative solution. The obtained molded body is degreased and purified after demolding and then sintered. Thereby, a highly pure and transparent silica glass product can be produced.

  The slurry is cooled in a range of 10 ° C. or less and 1 to 120 minutes. This cooling increases the viscosity of the slurry and does not cause aggregation or sedimentation of the powder even if the stirring is stopped. The cooled slurry is then injected into a resin or metal mold heated to a temperature not lower than the gelation temperature of the cellulose derivative aqueous solution and not higher than 150 ° C., specifically 70 to 120 ° C.

  In the mold, the slurry containing the cellulose derivative is gelled and moisture is evaporated to form a strong molded body. Evaporation of water is sufficient to maintain the required strength of the molded body when releasing the mold, and does not need to be completely removed.

    The degreasing treatment is performed in an air atmosphere at a temperature of 300 to 900 ° C. at a temperature rising rate of 1 to 5 ° C./min. When the temperature reaches the temperature range, the degreasing treatment is held for 3 to 6 hours until the degreasing treatment is completed to room temperature. It is allowed to cool. The purification treatment is preferably carried out at 500 to 1300 ° C. for 0.5 to 5 hours in a chlorine atmosphere. This treatment removes impurities, especially alkali metals and alkaline earth metals, in the silica molded body, suppresses the dislocation of silica glass to cristobalite during vitrification, and causes damage or chipping due to cracks in the product, or fine surface. There is no occurrence of unevenness due to cracks.

  The silica molded body produced by the production method of the present invention is sintered at a temperature of 1200 to 1700 ° C. for 5 to 30 minutes, preferably under reduced pressure.

  The present invention will be specifically described below, but the present invention is not limited to this.

Example 1
Silica fine powder having an average particle size of 1.5 μm was added to deionized water to prepare a silica slurry having a solid content of 80% by mass. After heating this to 80 degreeC, 5 mass% of methylcellulose whose weight average molecular weight is 290,000 g / mol was added little by little with respect to the silica fine powder solid content, and was mixed. The obtained methylcellulose-containing silica slurry was filled in an injection cylinder and cooled at 5 ° C. for 10 minutes. The cooled methylcellulose-containing silica slurry was injected into a mold heated to 80 ° C., held for 1 minute, and then released. The obtained molded body was degreased at 600 ° C. for 20 hours in an oxygen atmosphere, and then purified at 1200 ° C. in a hydrogen chloride atmosphere. Subsequently, a sintering treatment was performed at 1450 ° C. for 10 minutes at 13.3 Pa to obtain a 10 × 10 × 100 mm transparent silica glass block. This glass block had an average cell density of less than 0.1 / cm ³ and a shrinkage rate of 8%.

Example 2
A transparent silica glass block having a size of 10 × 10 × 100 mm was obtained in the same manner as in Example 1 except that 1% by mass of methylcellulose having a weight average molecular weight of 400,000 g / mol was used. This glass block had an average cell density of less than 0.1 / cm ³ and a shrinkage of 5%.

Comparative Example 1
In Example 1, injection molding was carried out in the same manner as in Example 1 except that the cooling in the injection cylinder was set to 20 ° C. However, the strength of the molded product was weak and a good molded product could not be obtained.

Comparative Example 2
A transparent silica glass block having a size of 10 × 10 × 100 mm was obtained in the same manner as in Example 1 except that the cooling in the injection cylinder was 50 ° C. and the weight average molecular weight of methylcellulose was 700,000 g / mol. . The resulting silica glass block had large bubbles and an average cell density of 1.2 / cm ³ .

The production method of the present invention is industrially useful because a silica glass product having a complicated shape can be produced accurately and inexpensively without mixing of bubbles.

Claims (8)

In a slurry containing silica fine powder heated to 100 ° C. or lower and a gelling temperature of the aqueous methyl cellulose solution and water, the methyl cellulose having a 2 mass% aqueous solution of 30,000 mPa · s or more is 0.1 to 0.1% of the solid content of the silica fine powder. Silica characterized by being added and dispersed in a range of 10% by mass, cooled for 1 to 120 minutes at a temperature of 10 ° C. or lower, and injected into a mold heated to a gelling temperature of a methylcellulose aqueous solution or higher and 150 ° C. or lower. Manufacturing method of a molded object. 0.1 to 10% by mass of methyl cellulose having a weight average molecular weight of 190000 to 530000 g / mol with respect to the solid content of the silica fine powder in a slurry containing silica fine powder heated to a temperature not lower than the gelation temperature of the methylcellulose aqueous solution and not higher than 100 ° C. and water. After being added and dispersed in the range, the silica molded body is cooled for 1 to 120 minutes at a temperature of 10 ° C. or less, and injected into a mold heated to a gelling temperature of a methylcellulose aqueous solution or higher and 150 ° C. or lower. Production method. The method for producing a silica molded article according to claim 1 or 2 , wherein the silica fine powder in the slurry is 40 to 85 mass% in terms of solid content. The method for producing a silica molded article according to claim 3, wherein the silica fine powder is 70 to 85 mass% in solid content. A method for producing a transparent silica glass product, comprising sintering a silica molded body obtained by the production method according to any one of claims 1 to 4 at a temperature of 1200 to 1700 ° C. 6. The method for producing a transparent silica glass product according to claim 5 , wherein a degreasing treatment and a purification treatment are performed before sintering the silica molded body. The method for producing a transparent silica glass product according to claim 6 , wherein the degreasing treatment of the silica molded body is performed at a temperature of 300 to 900 ° C. in an air atmosphere. The method for producing a transparent silica glass product according to claim 6 , wherein the purification treatment of the silica molded body is performed at 500 to 1300 ° C. in a chlorine atmosphere.