KR20010027999A - Composition for making silica glass with sol-gel process - Google Patents

Abstract

PURPOSE: A silica glass composition used for sol-gel process to make silica glass is provided which minimizes the adverse effect on the environment and produces silica glass more efficiently by using polyethylene imide, and minimizes the amount of the gelling agent. CONSTITUTION: A silica glass composition used for a sol-gel process is characterized by comprising silica particles, dispersing agent, deionized water, polyethylene imide as a main gelling agent, and sub-gelling agent; wherein the content of the main gelling agent, polyethylene imide, having a molecular weight of 1000000 or less is 0.1-12.5 pts.wt% based on the total weight of the silica particles, and the sub-gelling agent is selected from a group consisting of methyl formic acid and ethyl lactic acid.

Description

Composition for making silica glass with sol-gel process

The present invention relates to a composition for forming silica glass for a sol-gel process and a method for producing the same. More specifically, the gelation of the sol is reduced by reducing the content of the expensive pH reducing agent which acts as a gelling agent in the existing method through the conversion of the gelling mechanism, compared to the method of manufacturing silica glass according to the conventional sol-gel process. A reaction is accelerated and more environmentally friendly composition for forming silica glass for sol-gel processes.

The sol-gel process is a liquid phase process that not only provides high productivity and freely control the composition of the product, but it is also recognized as economical because the manufacturing process is generally performed at a low temperature compared to the existing method, and it is bulk glass through the sol-gel process. There have been numerous attempts to produce high silica glass, in particular. These attempts can be broadly classified into two types: sol-gel processes using alkoxides and particle sol-gel processes using ultrafine particles that are small enough to have colloidal properties. Of these two methods, the alkoxide-based method is known to have a limit in size, but is less economical.

In order to solve the problem, a sol-gel process using ultrafine particles has been proposed. According to this method, it is a useful method that can manufacture a large size silica glass of a certain size or more and economically produce high-purity silica glass such as an over-cladding tube for an optical fiber or a semiconductor manufacturing. A brief description will be given of a technique for preparing silica glass using the ultra-fine particle sol-gel process.

General processes in the sol-gel process include (1) preparation of silica sol, (2) gelation of sol, (3) drying of gel, and (4) vitrification through heat treatment of dry gel.

Looking at the manufacturing process in more detail, first, ultra-fumed silica particles (particles of less than 100m ² / g), the binder and the dispersant are mixed and dispersed in water to form a sol. As the binder, polyethyloxazoline, polymethyloxazoline, polyacrylamide-based polymers, etc. are used, and these polymer materials increase the bonding strength between particles in the gel due to their adsorption properties, thereby preventing cracking during drying of the wet gel. Increase the strength of the dry gel. In addition, as the dispersant, tetramethylammonium hydroxides and tetraethylammonium hydroxides, which are quaternary ammonium hydroxides exhibiting high pH characteristics, are added. Leads to 10 or more.

The sol prepared as described above is allowed to stand at room temperature for at least 24 hours after sealing to stabilize the sol. The stabilized sol is then added with a gelling agent (primarily ethyl lactate, methyl lactate, ethyl formate, methyl formate, etc.) and a water soluble aliphatic ester of an acid. The sol mixture is poured into a mold to obtain a tubular shaped body before the gelation reaction occurs, and gelled in the mold When the gelation is completed and has a certain strength, the gel is separated from the mold and dried .

Thereafter, the dried gel is first heat treated to remove organic matter in the gel. Subsequently, hydroxyl group and impurity removal reaction and sintering reaction are performed on the gel from which the organic substance has been removed, thereby completing a high purity silica glassy overcladding tube.

According to the method, more than 1 kg of large silica substrate can be easily prepared through the sol-gel process. However, this method has a disadvantage in that a highly toxic gas is generated in the step of removing the first organic matter during the manufacturing process using polyoxazoline, a polymer material that may cause environmental pollution as a binder. In addition, there is a disadvantage that the price of the pH reducing agent is expensive.

The technical problem to be achieved by the present invention is to solve the above problems by applying a polymer material less toxic than conventional silica glass manufacturing method by a conventional sol-gel process to minimize environmental pollution, as well as to minimize the polymer By changing the gelation mechanism of the sol, the silica glass can be economically and environmentally friendly to reduce the amount of expensive pH reducing agents acting as a gelling agent in the conventional method and to promote the same or more gelation reactions. It is to provide a composition for forming silica glass.

In the present invention to achieve the above technical problem,

A silica glass composition for a sol-gel process comprising silica particles, polyethyleneimide as a main gelling agent, an auxiliary gelling agent, a dispersing agent, and deionized water.

The present invention is characterized by using polyethyleneimide as the main component of the gelling agent and using a pH reducing agent applied as a gelling agent conventional in the conventional invention as the gelling aid. The use of the gelling agent having such a composition eliminates the use of highly toxic polymers compared to the conventional method, and at the same time reduces the content of the conventional gelling agent, a pH reducing agent, while exhibiting more gelation characteristics than the conventional one. .

The polyethyleneimide preferably has a molecular weight (M _w ) of 1,000,000 or less. If the molecular weight of the polyethyleneimide is out of the above range, it is not preferable because the viscosity of the sol in the addition process of the gelling agent and the subsequent process is increased.

The conventional gelling agent may be used as long as it is a material generally used in the manufacture of silica glass, and specific examples thereof include ethyl lactate, methyl lactate, ethyl formate, methyl formate, and the like.

The amount of the polyethyleneimide as the main gelling agent component is preferably 0.1 to 12.5 parts by weight, more preferably 1.25 to 6.25 parts by weight based on 100 parts by weight of the dispersant added to the initial sol. In addition, the use amount of the conventional gelling agent is a much smaller amount than the conventional pH reducing agent is used as the maximum addition amount is adjusted so that the gelation does not occur compared to the dispersant in the conventional method.

Hereinafter, a method of manufacturing silica glass by a sol-gel process using the silica glass composition according to the present invention will be described.

First, silica, dispersant and deionized water are mixed and then a sol is formed. In some cases, an additive such as a plasticizer may be further added in addition to the dispersant during sol formation. Herein, the dispersant and the plasticizer are not particularly limited as long as they are materials commonly used in the production of silica glass. And the content of each substance is also normal.

As a dispersant, tetramethylammonium hydroxide and tetraethylammonium hydroxide which are quaternary ammonium hydroxides are used. These materials not only help the silica to be uniformly dispersed in the composition, but also serve to electrostatically stabilize the sol in which the silica is dispersed. In addition, a polyhydric alcohol (polyhydric alcohol) is used as a plasticizer. Specific examples include glycerin, ethylene glycol, 2-methylpropane-1,2,3-triol, and the like.

Then, a gelling agent is added to the formed sol, and then a bubble is removed from the sol by using a vacuum pump for a certain time. At this time, this defoaming process may be performed before the gelling agent is added. As the gelling agent, a mixture of polyetherimide and a conventional gelling agent is used as described above. Typical gelling agents are water-soluble aliphatic esters of acids selected from the group consisting of formic acid, lactic acid, and glycolic acid, and one or more selected from methyl formate, ethyl lactate, and the like.

The sol formed according to the above procedure is injected into a mold in which a tubular shaped body can be obtained while maintaining fluidity before the gelation reaction occurs, and then gelled. Then, when the gelation is completed after a predetermined period of time, the gelled result is removed from the mold.

Then, the gel taken out of the mold is dried at a temperature of 30 to 80 ° C and a relative humidity of 65 to 80%.

Subsequently, the dried gel is heat-treated at 300 to 600 ° C. (raising rate: 5 to 50 ° C./hr) to remove organic matter remaining in the gel. Then, it heats up at 500-1000 degreeC (heating rate: 100 degreeC / hr), and heat-processes for predetermined time. During the heat treatment process, a high purity process is performed using a chlorine gas atmosphere, in which residual hydroxyl groups and other metallic impurities are removed. At the same time, oxygen or a fluorine compound gas is flowed to remove the chlorine component remaining in the silica molded body. The heat treatment temperature at this time is preferably carried out in 900 to 1100 ℃ section.

Thereafter, the resultant is heated to 1300 to 1500 DEG C in a helium gas atmosphere and heat treated at that temperature for several tens of minutes to several hours to complete the silica glass tube.

Hereinafter, the present invention will be described with reference to the following examples, but the present invention is not limited only to the following examples.

Example 1

Using a blending apparatus, 1000 g of ultrafine fumed silica powder (Aerosil OX-50, Degussa), 1000 g of deionized water, and 200 g of TMAH were sufficiently mixed to form a sol. Subsequently, the mixture was defoamed sufficiently for at least 10 minutes using a vacuum pump, and then sealed and left at room temperature and in air for 24 hours to stabilize the sol.

50 g of aqueous polyethyleneimide solution and 20 g of ethyl lactate were added to the sol, followed by uniform mixing. Herein, the aqueous solution of polyethyleneimide was used as a diluent solution in which the amount of polyethyleneimide was 5wt%, and the molecular weight (M _w) of the polyethyleneimide used was 750,000. The mixture obtained above was injected into a tube-molding mold in the state in which fluidity was maintained before gelation occurred, and molding was performed.

When the gelation was completed, the wet gel was separated from the molding mold and dried for 72 hours in a thermo-hygrostat controlled at 25 ° C. and a relative humidity of 80%.

Then, the dried gel was heated to 500 ° C. at a temperature increase rate of 10 ° C./h, and heat-treated at this temperature for 5 hours to remove organic matter in the dried gel. The organic-free gel was heated to 900 ° C. at 100 ° C./hr and maintained at this temperature for 5 hours. At this time, the heat treatment process was carried out in a chlorine gas atmosphere to remove the hydroxyl group and metal impurities. After the chlorine gas heat treatment was performed up to 900 ° C., the chlorine component remaining in the silica molded body was removed by maintaining the oxygen atmosphere while increasing the temperature to 1100 ° C. at a rate of 100 ° C./hr.

Finally, the silica glass tube was manufactured by heating up to 1350 degreeC by the temperature increase rate of 100 degreeC / hr in helium gas atmosphere, and sintering at this temperature for 1 hour.

Example 2

A silica glass tube was prepared in the same manner as in Example 1, except that 100 g of polyethyleneimide aqueous solution and 20 g of ethyl lactate were used instead of 50 g of aqueous polyethyleneimide solution and 20 g of ethyl lactate.

Example 3

A silica glass tube was prepared in the same manner as in Example 1, except that 50 g of polyethyleneimide aqueous solution and 20 g of ethyl lactate were used instead of 100 g of aqueous polyethyleneimide solution and 10 g of ethyl formate.

Example 4

A silica glass tube was prepared in the same manner as in Example 1, except that 50 g of polyethyleneimide aqueous solution and 30 g of ethyl lactate were used instead of 100 g of polyethyleneimide and 5 g of ethyl formate.

Comparative Example 1

Silica glass was prepared according to the same method as Example 1 except that 50 g of polyethyleneimide aqueous solution and 30 g of ethyl lactate were added to 2.5 g of polyethyloxazoline and 50 g of ethyl lactate were used for the preparation of the first silica sol. The tube was prepared.

Comparative Example 2

A silica glass tube was prepared in the same manner as in Example 1, except that 50 g of polyethyleneimide and 50 g of ethyl lactate were used instead of 50 g of polyethyleneimide.

According to Example 1-4, the gelation characteristics were equal to or higher than that of Comparative Example 1, thereby avoiding the use of toxic polymer polyethyloxazoline and reducing the use of expensive pH reducing agents. To obtain an environment-friendly and economical silica glass composition

On the other hand, in the case of using only polyethyleneimide as the gelling agent as in the case of Comparative Example 2, the strength of the gel is not sufficient, it is not possible to produce a silica glass having the desired physical properties was not preferred.

According to the present invention, it is environmentally and economically economical by minimizing the conversion of gelation mechanisms and the use of expensive pH reducing agents through the adoption of more environmentally friendly polymer materials compared to the production of silica glass according to a conventional sol-gel process. Silica glass can be prepared.

Claims (4)

A silica glass composition for a sol-gel process comprising silica particles, polyethyleneimide as a main gelling agent, an auxiliary gelling agent, a dispersing agent, and deionized water. The silica glass composition for a sol-gel process according to claim 1, wherein the cogelling agent is at least one selected from the group consisting of methyl formate and ethyl lactate. The silica glass composition for sol-gel process according to claim 1, wherein the main gelling agent content is 0.1 to 12.5 parts by weight based on 100 parts by weight of silica particles. The silica glass composition for sol-gel process according to claim 1, wherein the polyethyleneimide has a molecular weight (M _w ) of 1,000,000 or less.