JP2006232582A - Method for producing transparent silica glass product - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a transparent silica glass product, by which a silica glass product having a relatively complicated shape can be produced at a low cost with good productivity. <P>SOLUTION: The method for producing the transparent silica glass product includes (A) a step for preparing silica glass granules by mixing silica glass primary particles having diameters of ≤1 μm and water and drying the resulting mixture, (B) a step for obtaining a sintered powder by sintering the silica glass granules, (C) a step for preparing high concentration slurry containing 80-85 mass% silica particles by mixing the sintered powder with pure water and silica balls, then pulverizing the resulting mixture to obtain high concentration 70-78 mass% slurry, removing the silica balls from the slurry, and drying the slurry, (D) a step for casting the high concentration slurry in a mold, and (E) a step for taking out the formed article from the mold, and subjecting the formed article to drying/purifying treatment and vitrifying treatment. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

 The present invention relates to a silica glass product used in the fields of the optical equipment industry, the lighting lamp industry, the physics and chemistry equipment industry, and more particularly to a method for producing a transparent silica glass product having a relatively complicated shape such as a reflector.

 Conventionally, in the production of transparent silica glass products having a relatively complicated shape made of silica glass, a method of welding and assembling simple shaped members by fire processing, a method of processing a silica glass bulk body using machining technology, A method of forming using a hot press forming method has been adopted. In the assembly method by welding, most of the steps are performed manually, requiring a great deal of skill and time, and further, there is a problem in that the outer part is damaged due to high heat generated during fire processing and the appearance is damaged. . In machining technology, cutting using a grindstone or the like is performed, but since silica glass is a brittle material with high hardness, it takes a very long time to cut, and chipping and other chipping frequently occur and input. There was a problem that enormous energy to do. Furthermore, in the molding by the hot press molding method, quartz glass exhibits a high viscosity of logη of 5 or higher even at 2000 ° C, so the equipment to be used is expensive, and there are practically no molds that can withstand high-temperature pressing. In addition, even when commonly used carbonaceous materials are used, it reacts with silica glass at high temperatures, and its consumption is severe and needs to be replaced frequently. There is a problem in that the manufacturing cost must be increased.

As a method for solving the above-mentioned problems and producing a transparent silica glass product inexpensively and with high productivity, a so-called cast molding method in which a slurry in which silica glass powder is dispersed in a solution is molded in a mold has been proposed. . As a conventional casting method of silica glass products, for example, as shown in Patent Document 1, a silica fine powder of 10 to 500 nm is used, mixed with water and dried, and then heat-treated to have a particle size of 0.5 to several tens of μm. A method in which silica glass particles are formed, dispersed again in water to form a slurry, cast into a mold, and fired. As shown in Patent Document 2, a slurry of silica powder and water is prepared in two stages, dried to produce silica particles of less than 1 mm, and cast into a mold, or as shown in Patent Document 3 There has been proposed a method in which monodispersed particles having a uniform particle size are dispersed in water or an organic solvent to which a binder is added to form a slurry, which is molded by centrifugal casting. However, the manufacturing method of Patent Document 1 has a disadvantage that the viscosity of the slurry is low and a product having a simple shape can be manufactured, and a large product cannot be manufactured. In addition, in the production method of Patent Document 2, since silica powder is added for each step of slurrying, the viscosity of the slurry cannot be made sufficiently high, and even if it is poured into a mold, it causes mold leakage and is particularly good. There was a drawback that silica glass products having complicated shapes could not be produced. Furthermore, the production method of Patent Document 3 has a drawback in that it makes it difficult to produce a transparent silica glass product in which many impurities and bubbles are contained in the silica glass product because an organic substance is used as a binder.
JP-A 64-56331 JP-A-8-59222 Japanese Patent Laid-Open No. 5-124828

 In view of the current situation, the present inventors have continued intensive research, and as a result, silica glass primary particles of 1 μm or less and water are mixed, dried to produce silica glass granules and sintered with water. After mixing, pulverizing and drying, the slurry is made into a high-concentration slurry of 80 to 85% by mass, then cast into a mold and vitrified to produce a transparent silica glass product with a relatively complex shape at low cost and high productivity. The present invention has been completed by finding that it can be easily produced. That is,

 An object of this invention is to provide the method of manufacturing a highly purified transparent silica glass product cheaply and with sufficient productivity.

 Another object of the present invention is to provide a method for easily producing a high-purity transparent silica glass product having a relatively complicated shape.

 The present invention to achieve the above object is (A) a step of mixing silica glass primary particles of 1 μm or less and water and drying to produce silica glass granules, and (B) sintering the silica glass granules. Step of making sintered powder, (C) The sintered powder is mixed with water, pulverized into a slurry of 70 to 78% by mass, and dried to a high concentration of 80 to 85% by mass of silica glass particles It consists of the following steps: a step of forming a slurry, (D) a step of casting a high-concentration slurry into a mold, and (E) a step of taking out the molded body from the mold, drying, purifying, and further vitrifying. The present invention relates to a method for producing a transparent silica glass product.

 Silica glass primary particles of 1 μm or less are used as the raw material of the present invention. This silica glass primary particle is a sol-gel method using ethyl silicate, a method of thermally oxidizing waste silicon fine particles, a method of hydrolyzing silicon tetrachloride Etc. are manufactured. Regardless of which method is used, each element of sodium, potassium, lithium, calcium, magnesium, aluminum, iron, titanium, copper, nickel, and boron in the silica glass primary particles is preferably 1 ppm or less. In addition, water having an electric conductivity of less than 10 μs is suitable as the water mixed with the silica glass primary particles.

 In the production method of the present invention, high-purity silica glass primary particles are used, and they are mixed with water without using an impurity mixed material such as an organic binder to produce a high-concentration slurry. By doing so, a transparent silica glass product can be produced at a low cost, with high productivity, and in a relatively complicated shape.

In the production method of the present invention, as described above, silica glass primary particles having a size of 1 μm or less and water can be supplied and exhausted so that the concentration of the silica glass primary particles is 60 to 70% by mass. Silica glass balls are introduced into the vessel and 40% by weight or less of silica glass primary particles are introduced, and a rotating cylindrical container is stirred while rotating at a speed of 10 to 20 rpm, and dried to produce silica glass granules. To do. In the stirring, if the concentration of the silica glass primary particles is less than 60% by mass, the treatment time is long and undesirable, and if it exceeds 70% by mass, the resistance of the slurry becomes very large and stirring becomes impossible and expensive equipment is required. Further, it is necessary to add an acid as a pH adjusting agent, and post-treatment becomes difficult. Further, by mixing the silica glass balls, the particle size distribution of the silica glass granules is narrowed, and not only the working time after the next step can be shortened, but also the contamination by foreign matters and impurities due to the abrasion of the stirring blades can be reduced. The silica glass granules are dried by blowing air heated to 100 to 150 ° C. in a rotating cylindrical container at a rate of 10 to 20 m ³ / min. The final slurry has a water content of 5 mass. The particle size of the silica glass granules is preferably in the range of 0.5 to 100 μm. If the water content of the slurry exceeds 5% by mass, a separate drying step is required before the sintering step, resulting in high costs. Moreover, when the silica glass granule range exceeds the above range, it takes a long time to produce a slurry, and when the silica glass granule range is less than the above range, strong granules cannot be obtained.

In order to give the silica glass granule an appropriate granule skeleton strength, heat treatment is applied to obtain a sintered powder in order to eliminate the influence of pH. Without this heat treatment, the strength of the granule skeleton is weak, and cracks and cracks occur in the molded product in the next step. Further, in order to reduce the cost of heat treatment, it is carried out in an air atmosphere. At that time, a silica glass container such as a crucible is used, and silica glass granules are filled therein and covered with a quartz glass plate. It is important to fill the silica glass granules so that the apparent density is 0.6 g / cm ³ or more. Shake well when filling. If the packing density is non-uniform or less than the above-mentioned packing density, the sintered state is non-uniform and a homogeneous high-concentration slurry cannot be obtained. The heating temperature for sintering is preferably in the range of 1220 to 1250 ° C. in an air atmosphere. When the sintering temperature exceeds the above temperature range, silica glass granules are fused to the inner wall of the container, and it takes time to disintegrate the glass, resulting in poor working efficiency. Furthermore, the silica glass granule becomes very hard, the inner wall of the container is shaved, and foreign substances and contaminants are mixed into the slurry. On the other hand, if the temperature is too low, the strength of the granule skeleton is lowered, and cracks and cracks are likely to occur in the product.

 The sintered powder obtained in the above step is then introduced into a rotating cylindrical airtight container together with water and, if necessary, a silica glass ball. The ratio of the sintered powder is preferably 70 to 78% by mass. Also, the inner wall of the rotating cylindrical airtight container to be used is preferably covered with a lining material such as high-purity polyurethane or silica glass to prevent impurities from entering. The rotational speed of the rotating cylindrical airtight container is adjusted to 10 to 100 rpm. The working time of the rotating cylindrical airtight container varies depending on the production amount of the silica glass sintered powder, but takes about 1 to 7 days. Silica glass balls introduced into the rotating cylindrical airtight container should be 100% by weight or less of the sintered powder, and a silica glass ball having a diameter of 20 to 25 mm and a silica glass ball having a diameter of 25 to 35 mm has a mass ratio of 1: 2. Mix in proportions. When the silica glass ball exceeds 100% by mass of the sintered powder, the lining layer is scratched and impurities are mixed.

 A silica glass granule concentration of 70 to 78% by mass is obtained by the above operation. If the silica glass balls are left in the slurry, the slurry will solidify in the vicinity thereof, so that they are removed, and then the open rotating container inclined at an angle of 10 ° to 60 ° with respect to the central axis It is introduced into the inside, heated in a clean atmosphere at room temperature to 50 ° C. and dried to obtain a highly concentrated slurry. The moisture evaporation rate in the drying is preferably 50 g / hour or less per kg in the initial stage and 5 g / hour or less in the final stage with a gradient. If the moisture removal rate is fast to the end, solidification proceeds near the surface of the slurry and a non-uniform slurry is formed. In addition, when it is slow from the beginning, it takes a very long time to reach a predetermined moisture content, and the working efficiency is poor. This drying results in a high-concentration slurry in which the silica glass particle concentration in the slurry is 80 to 85% by mass, and the particle size distribution of the silica glass particles has a shoulder in 1 to 6 μm and 15 to 40 μm, and has a peak in the range of 6 to 15 μm. The particle size distribution is as shown in FIG. By having this particle size distribution, the high-concentration slurry can maintain fluidity and can be gravity-cast into a mold, so that a product having a complicated shape can be accurately produced. However, when the particle size distribution of the silica glass particles is a simple one-peak type as shown in FIG. 2, it is difficult to release during casting or cracks and bubbles occur, and it is difficult to obtain a highly accurate product. The rotational speed of the open-type rotating container during drying should be 5 rpm or less to reduce entrainment of bubbles. In addition, since the open-type rotating container has the above-described inclination, stress due to the inclination is applied to the high-concentration slurry, and the fluidity of the high-concentration slurry having high viscosity is maintained and a uniform slurry can be formed.

 The high-concentration slurry having a silica glass particle concentration of 80 to 85% by mass is then cast into a mold, but the mold used in the present invention has an outer mold and a middle mold so that a product having a complicated shape can be molded. A mold is used. Further, the mold is manufactured as an integral mold. Considering the ease of mold release, a split mold with two or more splits is preferable, but a split trace remains after molding, which is not preferable because the appearance of the product is impaired. A hygroscopic material is selected for the outer mold of the mold. Ceramics, gypsum, porous resin, and the like can be used as the hygroscopic material, but gypsum is preferred because of the pore diameter, handling, cost, etc. of the mold material. A material having no pores is selected for the middle mold. If the pores are present, the surface state of the resulting molded article is deteriorated, and the middle mold absorbs water and contracts, resulting in cracks. Examples of the material that does not substantially have pores include metals, plastics, ceramics, and the like, but rubber elastic bodies such as silicone rubber are preferable from the viewpoint of mold manufacturing cost, days, mass productivity, and mold releasability. When the material is high in hardness, the slurry adheres to the middle mold and takes time to release, and cracks may occur, resulting in a decrease in product yield. Further, the outer mold of the mold may be provided with a compressed air discharge port at a portion where the thickness changes, a portion where the shape change is large, or a fine portion, and an air line through which compressed air is sent.

 The high-concentration slurry has a very high viscosity and dilatancy characteristics, so that it is possible to obtain a compact close to the closest packing by suppressing variation in density due to settling of silica glass particles. Gravity casting is used in the casting process of the high-concentration slurry into the mold. As a result, the slurry can be filled up to a minute portion in the mold having a relatively complicated shape, and a hard molded article having good transferability can be produced, and a highly accurate transparent silica glass product can be produced. However, with the conventional pressure casting method, it becomes difficult to remove the molded body from the middle mold because the middle mold gets stuck, and the middle mold is deformed during pressurization because the middle mold is made of a rubber elastic body. However, the shape changes and cracks occur in complex parts with irregularities. This is a so-called spring back phenomenon that occurs when the elastic body tries to return to its original shape when the molding pressure is removed.

 The molded body released from the mold is allowed to stand for 4 hours every 50 ° C. from room temperature to 200 ° C. and dried. At this time, the atmosphere may be an air atmosphere in consideration of cost. The obtained molded body is preferably subjected to a purification treatment under the condition that an HCl-containing gas is allowed to flow at 0.5 L / min or more and the temperature is set to 900 to 1200 ° C. As a result, a product in which impurities are removed from the surface layer and cracks are prevented is obtained.

The dried molded body is heated to a temperature of 1200 to 1550 ° C and vitrified. Up to 1200 to 1400 ° C, it must be kept in a reduced pressure atmosphere of 10 Pa or less and held for 1 to 5 hours every 100 ° C increase. Good. By this holding, a finally transparent silica glass body can be obtained without taking a long time. Moreover, in the range of 1400-1550 degreeC, it heats under the pressure of 2 * 10 < ⁵ > Pa or less under inert gas. As the inert gas, He, N ₂ , Ar, or the like is used.

 FIG. 3 shows a schematic process flow of the method for producing the transparent silica glass product of the present invention.

 Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited thereto.

Example 1
Rotating cylinder with 130 kg of silica glass primary particles with an average particle size of 100 nm obtained by hydrolyzing silicon tetrachloride and 70 kg of water with an electrical conductivity of 5 μs, lined with high-purity polyurethane and equipped with air supply and exhaust It was introduced into a shaped container, and further 45 kg of silica glass balls were introduced and stirred. One hour after the start of stirring, 10 m ³ / min of air that was passed through a HEPA filter and was warmed to 130 ° C. was flowed to gradually evaporate the water. After about 30 hours, silica glass granules having a water content of 0.5% by mass and a particle size range of 1 to 80 μm were obtained.

Silica glass granules were filled into a plurality of silica glass crucibles having a diameter of 300 mm and placed in an atmospheric furnace. For filling, the packing density was 0.65 g / cm ³ while shaking the crucible using a shaker. The obtained filled silica glass granules were heated and sintered at 1225 ° C. for 10 hours. 100 kg of the silica glass sintered powder and 33 kg of ion-exchanged water are placed in a rotating cylindrical sealed container with a diameter of 500 mm and a length of 1000 mm, lined with high-purity polyurethane. Thus, a slurry containing about 75% by mass of silica glass particles was produced. The particle size distribution of the silica glass particles was measured using a laser diffraction type particle size distribution measuring instrument. As shown in FIG. 1, the particle size distribution had shoulders at 1 to 6 μm and 15 to 40 μm, and peaks in the range of 6 to 15 μm. Next, the silica glass balls were removed and the slurry was transferred to an open-type rotary container where it was further dried in clean air at 25 ° C. to obtain a high-concentration slurry having a solid content of silica glass particle concentration of 82% by mass. The inside of the rotating cylindrical airtight container was covered with high-purity polyurethane, and the central axis was inclined at 45 ° with respect to the vertical axis. In the drying, moisture removal was performed with a gradient of 40 g / hour in the initial stage per 1 kg and 4 g / hour in the final stage, and the rotation speed of the rotating cylindrical sealed container at this time was 1 rpm. Next, the high-concentration slurry was introduced into a mold to produce a bowl-shaped reflector. For casting, a funnel was attached to the casting port, and after naturally pouring and filling, it was left as it was for 1 hour, and compressed air was blown away from the air inlet port provided in the outer mold. The obtained molded body was allowed to stand for 4 hours every 50 ° C. from room temperature to 200 ° C. and dried. Purified by flowing HCl-containing gas at 1.5 L / min to the dried molded body and heat-treating at 1200 ° C. for 1 hour. Next, hold for 2 hours each time the temperature rises up to 1200-1400 ° C in a reduced pressure of 10Pa, and further heat to 1400-1500 ° C in an inert gas atmosphere of 1 × 10 ⁵ Pa, then hold at 1500 ° C for 10 minutes for vitrification did. The obtained reflector was transparent and had a good shape.

Example 2
A transparent and well-shaped reflector was produced in the same manner as in Example 1 except that a high-concentration slurry containing 84% by mass of silica glass particles in Example 1 was cast into a mold while giving fine vibrations.

Comparative Example 1
Rotating cylinder equipped with 130 kg of silica glass primary particles with an average particle diameter of 3 μm obtained by thermal oxidation of waste silicon fine particles and 70 kg of water with electrical conductivity of 5 μs, and the inner surface is lined with high-purity polyurethane Into a shaped container, 45 kg of silica glass balls were further introduced and stirred. One hour after the start of stirring, air heated to 130 ° C. was allowed to flow at 10 m 3 / min to gradually evaporate water. After about 30 hours, silica glass granules having a water content of 1% by mass and a particle size range of 1 to 100 μm were obtained. 120 kg of this silica glass granule was filled while shaking in a plurality of silica glass crucibles having a diameter of 300 mm. The packing density of the silica glass granules was 0.6 g / cm3. A crucible filled with silica glass granules was placed in an atmospheric furnace and heated. The heat treatment was performed at 1300 ° C. for 10 hours. Next, 100 kg of the resulting silica glass sintered powder, 33 kg of ion-exchanged water, and 80 kg of silica glass balls were lined with high-purity polyurethane, placed in a rotating cylindrical sealed container with a diameter of 500 mm and a length of 1000 mm, and operated for 5 days at a rotation speed of 18 rpm. Thus, a slurry containing about 75% by mass of silica glass particles was produced. The particle size distribution of the silica glass particles in this slurry was unimodal as shown in FIG. The obtained slurry was heated in air at 25 ° C. in an open rotary container to obtain a high-concentration slurry having a solid content of silica glass particle concentration of 83% by mass. The water removal was performed with a gradient of 40 g / hour per kg at the beginning and 4 g / hour at the end. At this time, the rotational speed of the open-type rotating container was 1 rpm.

Next, the high-concentration slurry was introduced into a mold to produce a bowl-shaped reflector. At this time, gypsum was used as the material of the outer mold, and after 1 hour, the mold was released using 4 kg / cm ² compressed air. The high-concentration slurry was strongly adhered to the mold and was difficult to release. There were many cracks in the product that was forcibly released.

Comparative Example 2
A reflector was manufactured in the same manner as in Example 1 except that the solid content of the high-concentration slurry was 75% by mass. The high-purity slurry adhered to the mold and was difficult to release. Many cracks were found in the product after drying and vitrification.

  The production method of the present invention produces a transparent silica glass product having a relatively complex shape, which is used in fields such as the optical equipment industry, the lighting lamp industry, and the physics and chemistry equipment industry, at low cost and with high productivity. Some are industrially expensive.

The particle size distribution of the silica glass particle in the high concentration slurry of this invention is shown. The particle size distribution of the silica glass particle in the high concentration slurry of a comparative example is shown. It is a process flow figure of the present invention.

Claims (13)

(A) Step of mixing silica glass primary particles of 1 μm or less and water and drying to produce silica glass granules, (B) Step of sintering silica glass granules into sintered powder, (C ) A step of mixing the sintered powder with water and pulverizing to make a slurry of 70 to 78% by mass, followed by drying to obtain a high concentration slurry having a silica glass particle concentration of 80 to 85% by mass, (D) high Production of a transparent silica glass product comprising: a step of casting a concentration slurry into a molding; and (E) a step of taking out the molded body from the mold, drying, purifying, and further vitrifying. Method. 2. The method for producing a transparent silica glass product according to claim 1, wherein the primary particle size of the silica glass is 10 to 500 nm. 2. The method for producing a transparent silica glass product according to claim 1, wherein in the step (A), the silica glass granule has a moisture concentration of 5% by mass or less and a particle size in the range of 0.5 to 100 μm. 2. In the step (B), the silica glass granules are filled in a quartz glass container with a packing density of 0.6 g / cm ³ or more, and sintered at a temperature of 1220 to 1250 ° C. in an air atmosphere. Method for producing transparent silica glass products. In step (C), in addition to the sintered powder and water, the silica glass balls are further mixed and pulverized to make a slurry of 70 to 78% by mass, and then the silica glass balls are removed from the slurry and dried. 2. The method for producing a transparent silica glass product according to claim 1. The above drying is performed in a clean atmosphere at room temperature to 50 ° C. with an initial moisture evaporation rate of 50 g / hour or less per kg and a final moisture evaporation rate of 5 g / hour or less with a gradient, and silica glass particle concentration of 80 to 85 at the final stage. 6. The method for producing a transparent silica glass product according to claim 5, wherein the mass percentage is set to mass%. The method for producing a transparent silica glass product according to claim 5 or 6, wherein the particle size distribution of the silica glass particles in the high-concentration slurry has a shoulder at 1 to 6 µm and 15 to 40 µm, and has a peak at 6 to 15 µm. . In the high concentration slurry of step (C), the inner side is coated with high-purity polyurethane or silica glass, the central axis has an inclination of 30 ° to 60 ° with respect to the vertical axis, and the rotation speed is 1 to 100 rpm. 2. The method for producing a transparent silica glass product according to claim 1, wherein the method is performed in a rotating cylindrical container. 2. The method for producing a transparent silica glass product according to claim 1, wherein the casting is performed by gravity casting in the step (D). 10. The method for producing a transparent silica glass product according to claim 9, wherein vibration is applied during gravity casting. 2. The method for producing a transparent silica glass product according to claim 1, wherein the molding die is composed of an integrally molded outer die and a middle die, the outer die is gypsum, and the middle die is a rubber elastic body free from bubbles. 2. The transparent silica glass according to claim 1, wherein the purification treatment in step (E) is a treatment of heating to a temperature of 900 to 1200 ° C. in a vessel in which an HCl-containing gas is flowed at a flow rate of 0.5 L / min or more. Product manufacturing method. (E) In the vitrification treatment in step (E), the treatment is performed at 1200 to 1550 ° C., and the first treatment to 1200 to 1400 ° C. is performed at a temperature of 1 to 5 hours in a reduced pressure atmosphere of less than 10 Pa and every 100 ° C. rise. 2. The method for producing a transparent silica glass product according to claim 1, wherein the last treatment at 1400 to 1550 ° C. is carried out under an inert gas atmosphere at a pressure of 2 × 10 ⁵ Pa or less.