JPS61186231A - Production of glass tube - Google Patents

Abstract

PURPOSE:To produce a glass tube having uniform thickness in a short time, by gelatinizing a raw material consisting of an alkoxide of Si, etc. in a rotary container having a cylindrical inner face under specific time and temperature conditions, drying, and sintering it. CONSTITUTION:A Si alkoxide such as silicon tetramethoxide, etc. is sufficiently stirred and blended with ethanol, mixed with water containing a pH adjustor such as NH3, etc. to give a sol solution, which is put in a container which has a cylindrical inner face and is rotated in the circumferential direction. When the time of water addition is tb, the time when gelatinization starts and the sol solution loses substantially fluidity is te, the average temperature of the sol solution between the time tb and t is T1, and the average temperature of the sol solution between the time t and te is T2, the temperature of the sol solution is controlled in such a way that the time t which is in T1>T2 and tb<t<te exists, hydrolysis is advanced, and the sol solution is gelatinized. Then the gel is dried and sintered.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing shigarasu by a sol-gel method.

[Conventional technology]

Currently, methods for producing optical fiber preforms include the VAD method, in which glass particles such as 810T4 are passed through a flame and deposited on a target, and the resulting glass porous body is sintered into a glass lump. The mainstream method is to obtain This is an excellent method for obtaining high-purity porous glass at a relatively low cost. Since this method uses a gas phase reaction, it has the disadvantage that the substances that can be used as additives are limited to those that can be gasified.

Therefore, in recent years, as a method to compensate for this drawback, metal alkoxides mainly composed of 30% are hydrolyzed to obtain silica gel or silica gel containing additive elements, and after drying the silica gel, a process such as making it non-porous is performed to make transparent glass. Methods to obtain this are being actively researched.

For example, silicon tetramethoxide, etc.
After thoroughly stirring and mixing the alkoxide with ethanol, water is added and further stirred for hydrolysis. It is preferable to add a pH adjuster such as ammonia to this poet. The sol thus obtained is poured into a vibrator with one end sealed, and the sol is turned into a gel. Next, extrude this gel in ethanol, transfer it to another container, cover it with aluminum foil, etc. to prolong the drying time, and dry the gel by keeping it in a constant temperature bath at, for example, 60°C. . The gel shrinks as it dries, and drying is usually completed after several days.

The gel thus obtained is taken out and subjected to a nonporous treatment, for example, by heating in an oxygen-containing ■θ atmosphere.
It's about getting glass.

In addition, the present inventors have already developed a method in 1985, in which the sol liquid and particles with a size that does not form a colloid are mixed and then solidified to obtain a porous material, which is then dried and sintered to obtain glass.
The proposal was made in the specification filed on May 30th. This porous material contains particles larger than colloids and is not technically a gel. Its precursor is also not a sol liquid.

However, herein, the porous bodies obtained by the sol-gel method, including such porous bodies, are referred to as gels, and the precursor thereof is referred to as a sol liquid.

To make a glass tube using the above-mentioned sol-gel method, there is a method in which a sol solution is placed in a cylindrical container, and the central axis of the container is held horizontally, and the container is rotated to gel as it is [JP-A-58-99130]. However, when trying to make a glass tube using the method described in JP-A-58-99130, gelation takes time if the pH of the sol solution is low. If the pH is high, the viscosity increases rapidly during gelation, causing the tube to become distorted, while at an intermediate pH, it takes time for gelation to occur, causing the overwritten tube to become distorted.

The present invention relates to a method for manufacturing a glass tube with a uniform wall thickness by solving the drawbacks of the conventional method and obtaining a gel tube with a uniform wall thickness in a short time.

[Means for Solving the Problems] The present invention uses silicon alkoxide as at least one of the raw materials, and adds at least water to the resulting sol solution, which has a cylindrical inner surface and rotates in the circumferential direction. In the method of manufacturing a glass tube by gelling in a container, drying and sintering the gel, t is the time when water is added, and t8 is the time when gelation occurs and the Schizol liquid has substantially lost its fluidity. The average temperature of the sol liquid between tb and t is 7 times, and the average temperature of the sol liquid between t and te is Tl.
Then, it is effectively 'r, ) 'r.

The above object is achieved by a method for manufacturing a glass tube characterized in that the temperature of the sol solution is controlled so that a time t exists where tb < t < te.

When time t is taken just before gelation begins, 'rl-'r
It is most preferable to control the temperature so that , is maximized, but it is effective if Tl>T2.

In general, hydrolysis of alkoxide is an exothermic reaction, and gelation occurs from time t1) when hydrolysis starts to time t1 when fluidity is lost. shows a monotonous temperature rise up to
TILT! This is often the case. In this case, no matter which value t is chosen, it is unlikely that TI - Tl will exceed 10°C. Furthermore, when hydrolyzed in ammonia alkaline conditions, heat generation is rapid and gelation occurs quickly.

The method of the present invention is achieved by controlling the temperature.
, Tt > Tl, and preferably 'rl-
'i' is set to be about 1° C. or higher to reduce the gelation reaction rate, slow the change in viscosity, and prevent the tube from becoming distorted.

Specific methods of temperature control in the present invention include: (1) warming the container containing the sol solution in order to increase T1; cooling the container containing the sol solution in order to lower the 01 weight; or (2) , ■ are used together.

The heating means may be any conventional means, such as immersion in warm liquid or gas, or holding in a constant temperature bath or furnace, and the cooling may be carried out by any conventional means, such as holding in cold fluid, liquid nitrogen, cryogen, etc. You can use

In addition, it is preferable that the time t is just before gelation, and in order to know this t, prepare a contrast sol solution and heat the contrast sol to accelerate the gelation time, or The sol may be cooled so that gelation begins after the gelation start time of the contrast sol.

Alternatively, an experiment may be conducted under the same conditions and the time until gelation may be measured.

If t is known in this way, add water to the liquid containing the alkoxide to make a sol, heat the sol, and stop heating the sol a little before gelation, or cool it just before gelation. It is possible to maximize 'r, + 'r. Alternatively, it is also possible to prepare a gel solution, leave it as it is, and cool it a little before gelation.

The sol liquid may contain particles other than silica particles produced by hydrolysis, such as silica particles produced by a gas phase method, particles containing a dopant, and the like.

As an example, in FIG. 1, curve A shows an example of temperature change from tb to te in one example of gelation by a conventional method, and the temperature change when the present invention is applied to this is shown at curve end.

Further, in FIG. 2, the conventional method for the above-mentioned change in viscosity over time is shown as curve A, and the case where the present invention is applied to this is shown as curve A. In this manner, the method of the present invention suppresses a rapid increase in viscosity by cooling.

[Effect]

The problem that gelation takes a long time can be solved by increasing the temperature of the sol as described above.

The sudden increase in viscosity during gelation can be solved by lowering the temperature of the sol just before gelation. Therefore, according to the present invention, t is the time when water is added, t is the time when gelation occurs and the schizol has substantially lost its fluidity, t is the average temperature between tb and t of the sol, and Tl is the average temperature between t and t of the sol. The average temperature between T.

Then, TI>T2 and tb<t<t8
Both problems can be solved simultaneously by controlling the temperature of the sol solution so that a certain time t exists.

〔Example〕

The method of the present invention will be specifically explained below with reference to Examples.

Example 1 81 (OCH3) 4q, sv and ethanol 11.5
W was mixed, and water 91 containing two drops of 13% ammonia water was added thereto and further mixed. This liquid was poured into a pipe with an inner diameter of 8φ that was sealed at one end, and after the other end was sealed, it was cooled for several seconds with liquid nitrogen and then left at room temperature. The remaining sol solution that was not put into the pipe was continued to be observed as a control sample, and after a few minutes, when gelation started, the pipe was placed on its side and immersed in liquid nitrogen. After the sol liquid in the pipe was frozen, it was spun and rotated in the circumferential direction. After a while, the sol solution started to dissolve. At this time, the rotation speed was about 1000 rpm. As time elapsed, the sol turned into a gel, and a gel with a uniform thickness was obtained. It took about 10 minutes from mixing to completion of gelation. This was dried and sintered to obtain a glass tube.

Comparative Example 1 A gel tube was obtained in the same manner as in Example 1, except that the sol solution was not cooled after being put into the pipe and the pipe was immediately rotated. This gel had a non-uniform wall thickness and was extremely distorted.

Comparative Example 2 A gel tube was obtained in the same manner as Comparative Example 1 except that 6% ammonia water was used as the ammonia water and only one drop was added. It took more than 20 minutes for gelation to begin, and the resulting gel tube was distorted.

Comparative Example 3 The same procedure as Comparative Example 1 was carried out except that aqueous ammonia was not added, but the liquid did not gel even after 1 hour.

Example 2 A glass tube with a uniform wall thickness was obtained in the same manner as in Example 1, except that silica particles α1 α22 having a particle size of about 1,012 μm were added to water.

〔Effect of the invention〕

According to the present invention, a glass tube having a uniform wall thickness can be manufactured in a short period of time.

[Brief explanation of drawings]

FIG. 1 is a graph showing the change in temperature over time until the sol solution gels. A shows the conventional method, and A shows the method of the present invention. FIG. 2 is a graph showing the change in viscosity over time in the case of FIG. 1, where A shows the conventional method and A shows the method of the present invention.

Claims (1)

[Claims] (1) At least one of the raw materials is a silicon alkoxide, and a sol solution obtained by adding at least water is gelled in a container whose inner surface has a cylindrical shape and rotates in the circumferential direction. In the method of manufacturing a glass tube by drying and sintering, the time at which water is added is t_b, and the time at which gelation occurs and the sol has substantially lost its fluidity is t_e, which is between t_b and t of the sol. The average temperature of the liquid is T_1
, and the average temperature of the sol between t and t_e is T_2
Then, substantially T_1>T_2 and t_b<
A method for manufacturing a glass tube, comprising controlling the temperature of a sol solution so that a time t exists where t<t_e.