JPH0742124B2 - Method for forming quartz glass plate - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for forming a quartz glass plate.

[Prior Art] High-purity, defect-free large-sized synthetic quartz glass plates have low thermal expansion coefficient, excellent optical characteristics and chemical durability, and are therefore expected as substrate materials for displays and the like.

As one of the methods for producing synthetic quartz glass, which is conventionally known as a method for producing quartz glass by a gas phase reaction method, various raw material gases are made to flow from a burner to a seed rod for producing quartz glass, and a silicon compound is caused to emit an oxyhydrogen flame. While hydrolyzing in the medium, while rotating the vertically suspended seed rod, silica particles are deposited on the seed rod and sequentially grown to grow a porous base material, which is then heat treated to form glass. It is a method of converting.

Further, as a method for producing quartz glass by the Bernoulli method, which has been conventionally known as a method for producing other synthetic quartz glass, various raw material gases are supplied from a burner, and decomposed and vitrified in a flame such as an oxyhydrogen flame, It is a method of obtaining a glass ingot by depositing it on a target ball.

The synthetic quartz glass produced by the former method is extremely high in purity and has no defects, but due to its production method, it is substantially cylindrical and usually has a maximum diameter of about 5 inches.

On the other hand, synthetic quartz glass manufactured by the conventional method is
It is usually cylindrical, and depending on the manufacturing method, up to 200 mm-3
Although a diameter of about 00 mm can be obtained, it is technically difficult to manufacture a larger diameter, and when the size is increased, it is difficult to completely remove bubbles and the like.

[Problems to be Solved by the Invention] Therefore, it is difficult to manufacture a large quartz glass plate of 20 inches or more by any of the manufacturing method by the gas phase reaction method and the manufacturing method by the Benouy method described in the preceding paragraph. ,
The high-purity quartz glass ingot obtained by these methods needs to be molded by heating and pressing. Hereinafter, a cylindrical rod of high-purity quartz glass can be referred to as a quartz glass rod or a glass rod.

Conventionally, as a method of this molding, there is known a method in which a quartz glass rod is heated in a molding container made of carbon or the like at 1600 to 1800 ° C. and pressed from above (Japanese Patent Laid-Open No. 57- 67031, JP-A-57-92528 and others). However, there is a limit to the size that can be formed with a good yield by these methods, and for example, when a glass rod having a diameter of 4 inches and a length of 0.5 m is used, it is a limit to form an 8-inch square block. This is considered to occur because the rod is deformed during the forming process and the uniform deformation does not proceed due to the subtle temperature distribution in the furnace. It was the cause.

[Means for Solving Problems] The present invention has been made to solve the above problems, and a cylindrical rod of high-purity silica glass is molded at a high temperature to form a glass plate having a desired shape. In this case, the present invention provides a method for forming a quartz glass plate, characterized by using a forming container made of carbon in a heating furnace and pressurizing from a direction perpendicular to the axis of the cylindrical rod to perform heat forming.

As the quartz glass rod used in the present invention, a synthetic quartz glass cylindrical rod manufactured by the above-mentioned method is cut into a required length, treated with an organic solvent and 10 to 20% hydrofluoric acid, and attached to the rod. It is preferable to use the organic and metal oxides other than SiO ₂ after removing the metal ions, further washed with pure water and dried.

This is set in molding containers 2 and 3 made of carbon having a shape as shown in FIG. 1, particularly graphite, and a weight 4 made of graphite is placed from above and placed in a furnace. The furnace is preferably a resistance heating type furnace using a graphite heater or an induction heating furnace.

As shown in FIG. 2, the cylindrical glass rod used in the present invention is preferably ground in advance to prevent the glass rod from rolling or slipping on the bottom plate during heat forming, and the shape at that time is the rod. For the diameter d ₀ of
It is preferable that d in FIG. 2 is in the range of d / d ₀ = 0.9 to 0.99. Above this, the glass rod is not stable, and below this range, the grinding white is too large and the yield decreases, which is not preferable. Furthermore, when setting this rod in the molding container of FIG. 1, as shown in FIG. 3, a bottom plate including straight lines connecting the midpoints of two opposite sides of the upper surface of the rectangular glass plate to be obtained after molding. It is preferable to install the glass rod so that it lies sideways so that the axis of the glass rod 1, which is the object to be molded, is substantially included in the plane perpendicular to. For example, when this is installed so that the axis of the glass rod 1 is included on the diagonal line of the bottom plate, the distance that the glass should flow during the heat forming is greatly different between the center part and the end part of the rod, It is not preferable because it is difficult to obtain a uniform molded body.

Further, the basic constitution of the molding container is preferably as shown in FIG. 1, but in particular, as shown in FIG. 3, a vertically divided mold is formed so that a rectangular bottom plate and a prismatic molding chamber are formed on the bottom plate. A structure in which a plurality of is arranged is more preferable. This is because the thermal expansion coefficient of quartz glass, which is the object to be molded, and graphite, which is the material of the molding container, differ by about one digit, so that it prevents the occurrence of cracks, etc. in the glass that occur during the process of cooling to room temperature after thermoforming. This is because it has an effect. In particular, when molding at 1700 ° C or higher, glass and graphite sometimes react and adhere to each other, and the glass may be damaged.As a countermeasure, coat the inner surface of the molding container with SiC. Is more effective.

In the present invention, the atmosphere in the furnace at the time of heat molding does not become a limiting element of the present invention, but when graphite is used as the material for the molding container using the graphite resistance heating furnace, it must be an inert atmosphere. It is particularly preferable that the atmosphere is argon or nitrogen. Other inert gas such as helium may be used. However, since helium is extremely expensive, there is a problem in terms of economy.

The molding temperature adopted in the present invention is not generally determined depending on the viscosity of the quartz glass rod which is the object to be molded, but it is preferably in the range of 1600 to 1800 ° C. In the case than the low temperature which, severe devitrification of the quartz glass, and because of the high viscosity, practical not able to perform the shaping in, also, of SiO ₂ of silica glass in the case from the high temperature which It is not preferable because it causes severe scattering, which lowers the yield and damages the furnace.

The size of the glass rod as an object to be molded, the range of the ratio l ₀ / l ₁ of the length l ₀ of the long sides of the glass plate obtained after molding and the length l ₀ of the glass rod is 0.5 to 1.0 Is preferred. If the size is smaller than this, it is difficult to obtain a uniform glass plate with high dimensional accuracy, because the main component of the present invention, that is, the purpose of forming from the direction perpendicular to the axis of the rod, is not utilized.

Further, the ratio of the diameter d _{0 of the} glass rod to the length l ₂ of the short side of the glass plate after molding is preferably d ₀ / l ₂ = 0.1 to 0.6, but this is also due to the above reason.

[Example] Example 1 Diameter 120 mm and length 5 produced from silicon tetrachloride as a raw material.
A synthetic quartz glass ingot of 00 mm in weight and 12.4 kg in weight was molded into a graphite molding container as shown in FIG. 3 in which the inner dimension of the bottom plate was 510 mm square. -Random) is applied in a thickness of 0.5 mm) and carbon with a maximum output of 250 kw is used as a heating element 9
It was set in an electric furnace having inner dimensions of 000 mm (inner diameter) x 800 mm (height). At that time, a graphite weight was placed on the push rod on the upper surface of the ingot, and the load applied to the upper surface of the ingot was adjusted to be 50 kg.

Then, the inside of the furnace was evacuated by a vacuum pump to reduce the pressure to 0.05 Torr, and then the temperature increase was started while continuously reducing the pressure. When the temperature was raised to 1000 ° C. in 2 hours, the vacuum pump was stopped and argon gas was introduced into the furnace to 1 atmospheric pressure.
After that, the temperature was raised to 1750 ° C. in 2 hours and kept for 4 hours.

After this, the temperature is lowered to 1250 ° C in 1 hour, then to 1000 ° C 40
The temperature was lowered at ° C / hr, the electric furnace power was turned off, and the system was allowed to cool. After confirming that the temperature inside the furnace had cooled to room temperature, the graphite molding container was taken out of the furnace. The weight of the ingot after molding was 12.3 kg, which was a square plate having a side of 511 mm and a thickness of 21 mm, and no entrapped bubbles were observed inside, and it was extremely clean.

Example 2 Diameter 120 mm and length 5 produced from silicon tetrachloride as a raw material
The second is a synthetic quartz glass ingot with a diameter of 00 mm and a weight of 12.4 kg.
The bottom surface was ground as shown in the figure, and d ₀ = 120 mm, d = 115 mm (d /
d ₀ = 0.96) After setting the weight to 12.3 kg, it was washed in perchlorethylene and 10% HF, washed with water and dried. This was coated with a graphite molding container (inside of which the glass is in contact with glass) of silicon carbide powder (β-random, made by Ibikawa Electric Co., Ltd., β-random) with a thickness of 0.5 mm as shown in FIG. )put in,
900mm (inner diameter) with carbon of maximum output 250kw as heating element
It was set in an electric furnace having a furnace size of × 800 mm (height). At that time, a graphite weight was placed on the push plate on the upper surface of the ingot, and the load applied to the upper surface of the ingot was adjusted to 50 kg.

Next, the inside of the furnace was evacuated by a vacuum pump to reduce the pressure to 0.05 Torr, and then the temperature was started while continuously reducing the pressure. When the temperature was raised to 1000 ° C. in 2 hours, the vacuum pump was stopped and argon gas was introduced into the furnace to 1 atmospheric pressure.
After that, the temperature was raised to 1750 ° C. in 2 hours and kept for 4 hours.

After this, the temperature is lowered to 1250 ° C in 1 hour, then to 1000 ° C 40
The temperature was lowered at ° C / hr, the electric furnace power was turned off, and the system was allowed to cool. Then, after confirming that the temperature inside the furnace was cooled to room temperature, the graphite molding container was taken out of the furnace and the molding ingot was taken out.

The ingot weighed 12.2 kg, was a square plate with a side of 511 mm and a thickness of 21 mm, and it was extremely clean without any entrained bubbles inside.

Further, since the side surface of the synthetic quartz glass ingot was ground prior to heating and pressing, extremely stable pressure molding could be performed.

Comparative example manufactured using silicon tetrachloride as a raw material, diameter 120 mm, length 4
A synthetic quartz glass ingot of 00 mm in weight and 10.0 kg in weight was molded into a graphite molding container as shown in Fig. 4 with a bottom plate of 510 mm square. -Random) was applied in a thickness of 0.5 mm) so that the axis of the glass rod was perpendicular to the bottom plate surface of the molding container, and the same was set in the same furnace as in Example 1.
At that time, a graphite weight was placed on the push plate on the upper surface of the ingot, and the load applied to the upper surface of the ingot was adjusted to 50 kg.

Next, the inside of the furnace was evacuated by a vacuum pump to reduce the pressure to 0.05 Torr, and then the temperature was started while continuously reducing the pressure. When the temperature was raised to 1000 ° C. in 2 hours, the vacuum pump was stopped and argon gas was introduced into the furnace to 1 atmospheric pressure.
After that, the temperature was raised to 1750 ° C. in 2 hours and kept for 4 hours.

After this, the temperature is lowered to 1250 ° C in 1 hour and then to 1000 ° C 45
The temperature was lowered at ° C / hr, the electric furnace power was turned off, and the system was allowed to cool. Then, after confirming that the temperature inside the furnace was cooled to room temperature, the graphite molding container was taken out of the furnace and the molding ingot was taken out.

The ingot weighs 9.9 kg, has a side of 511 mm and a thickness of 17 mm.
However, many entrapped air bubbles were observed inside the plate, which are considered to be generated by bending the glass rod during molding.

In the above-mentioned embodiment, the quartz glass after molding has a plate shape, but the present invention is not limited to the plate, and generally when obtaining a block-shaped quartz glass molded body having a large thickness with respect to the bottom dimension. Applicable.

[Effects of the Invention] As described above, according to the present invention, it is possible to obtain not only small-sized and medium-sized cylindrical plates of high-purity silica glass but also large-sized glass plates with a high yield, and it is difficult to manufacture them conventionally. It is possible to manufacture a high-purity large-scale quartz glass plate which was

Moreover, by appropriately selecting the size of the glass rod before molding, a plate with an arbitrary thickness can be obtained, so that the yield is good without the step of slicing from the block, and the large size of the arbitrary thickness can be obtained. You can get a glass plate.

[Brief description of drawings]

FIG. 1 is an explanatory view of a molding container, FIG. 2 (a) is a cross-sectional view perpendicular to the axis of the rod showing the shape of a glass rod that is the object to be molded, and FIG. 2 (b) is the same. It is a side view. FIG. 3 is an explanatory view showing an embodiment of a molding container structure in which a plurality of vertical split molds are arranged. FIG. 4 is an explanatory view showing a conventional example. 1 ... glass rod, 2,3 ... molded container, 4 ... weight, 5 ... split container side plate, 6 ... split mold fixing bolt, 7 ... split container bottom plate

Claims (10)

[Claims] 1. When molding a cylindrical rod of high-purity quartz glass at a high temperature to form a glass plate having a desired shape,
The cylindrical rod placed in the molding container in the heating furnace,
A method for forming a quartz glass plate, which comprises pressurizing and heating from a direction perpendicular to the axis of the cylindrical rod. 2. The glass rod, which is placed on the bottom plate of the molding container such that the axes of the bottom plate and the glass rod are parallel or substantially parallel to each other, has a flat surface having substantially the same size as a glass plate of a desired shape. The method for molding a quartz glass plate according to claim 1, wherein pressure is applied from above through a pressing plate. 3. A glass rod, the surface of which is in contact with the bottom plate of the molding container and the surface of which is in contact with the pressing plate, is ground, and is a plane perpendicular to the bottom plate. The method for molding a quartz glass plate according to claim 2, wherein the glass rod axis is placed on the bottom plate of the molding container so as to substantially include the glass rod axis in a plane including a straight line connecting the midpoints. 4. A molding container comprises a bottom plate having a desired glass plate shape and a plurality of vertical split molds disposed on the bottom plate, and a columnar molding chamber having a bottom surface of the desired shape is formed on the bottom plate. The method for forming a quartz glass plate according to claim 1, wherein 5. The method for molding a quartz glass plate according to claim 1, wherein the atmosphere in the heating furnace is one atmosphere selected from argon, nitrogen and helium. 6. The method for molding a quartz glass plate according to claim 1, wherein the molding temperature is 1600 to 1800 ° C. 7. The desired glass plate shape is rectangular and the ratio l ₀ / l ₁ of the axial length l ₀ of the glass rod to the long side length l ₁ of the rectangular glass plate obtained after molding. Is 0.5 ~
Claim 1 characterized by being in the range of 1.0
A method for forming a quartz glass plate according to the item. 8. A desired glass plate has a rectangular shape, and the ratio d ₀ / l ₂ of the diameter d ₀ of the cross section of the glass rod and the length l ₂ of the short side of the rectangular glass plate obtained after molding is obtained. 0.1
The method for forming a quartz glass plate according to claim 1, wherein the range is from 0.6 to 0.6. 9. A molded container made of carbon, as claimed in claim 1, claim 2, claim 3 or claim 4.
A method for forming a quartz glass plate according to the item. 10. The method for molding a quartz glass plate according to claim 9, wherein the inner surface of the molding container is coated with SiC.