KR100321997B1 - Manufacturing method of silica glass by extrusion process - Google Patents

Abstract

According to the present invention, a silica glass is prepared by an extrusion process including a filling process of filling a brush in an extruder, a heating process of applying heat to the filled brush, and an extrusion process of extruding a gel formed through the heating process. In the extruder, a sol filled in the extruder is formed by mixing fumed silica with deionized water and dispersing with a dispersant, followed by mixing a silicon alkoxide having two alkoxide groups with a hydrolyzate hydrolyzed under a basic catalyst.

Description

Manufacturing method of silica glass by extrusion process {MANUFACTURING METHOD OF SILICA GLASS BY EXTRUSION PROCESS}

The present invention relates to a method for producing silica glass using a sol-gel process, and more particularly to a method for producing silica glass by an extrusion process.

The sol-gel process is a liquid phase process that not only freely controls the composition of the product, but also economically because the process is generally performed at low temperature.

In addition, the sol-gel process is a very useful process in the manufacture of photomask for semiconductor, high purity silica glass, etc. by using a high purity material from the starting material (starting material). Silica glass manufacturing method by the sol-gel process is largely composed of the following six steps.

In the first step, fumed silica is mixed with deionized water and a dispersant is mixed to disperse to make a uniform sol.

The method of using the fumed silica is disclosed in detail in FABRICATION OF SINTERED HIGH-SILICA GLASSES, invented and patented by Johnson, Jr., et al.

The second step is to gel the brush produced by the first step. A gelling accelerator is added to accelerate the gelling reaction of the sol.

The third step is to mature the gel.

The fourth step is to dry the gel using a predetermined drying means.

The fifth step is a process of removing organic matter, alkali metallic impurities, hydroxyl group (OH), etc. in the gel through low temperature heat treatment.

The sixth step is a process of sintering and vitrifying the gel after the organic material treatment to produce a high purity silica glass.

The method for producing silica glass as described above has a disadvantage in that the processing time is very long and continuous processing is not performed. US Patent No. 4,682,995, which was invented and patented by Klaassen et al., Discloses a method for producing silica glass that is capable of continuous processing and has a short process time using an extrusion process. However, in the formation of the gel using the extrusion process, the content of the silica powder of the sol is very important.

When the amount of the solvent, ie, the water, is relatively small, the strength of the gel produced is high while the dispersibility is low and air is more likely to be trapped. On the other hand, in the case of a relatively large amount of water, the dispersibility is good and it is advantageous to remove the air, but the strength of the gel produced is weak and the shrinkage during drying is likely to cause cracks and it is difficult to maintain an accurate shape There is this. In US Pat. No. 4,682,995, Klaassen uses an ammonium fluoride containing fluorine ions to improve the thixotropic properties of the sol, thereby increasing the content of silica particles. Improved strength.

However, although the content of silica particles has been increased and the strength has been improved, there is still a problem in that the strength is still weak to make a long gel. In addition, when a large amount of fluorine is used, and the length of the tube or rod to be produced is long, there is a problem that the composition is a high risk of nonuniformity.

In order to solve the above problems, an object of the present invention is to provide a method for producing silica glass by an extrusion process that can realize a high dispersibility of the brush, excellent pre-drying strength of the gel and shrinkage ratio after drying.

In order to achieve the above object, in accordance with the present invention, an extrusion process including a filling process for filling a brush in an extruder, a heating process for applying heat to the filled brush, and an extrusion process for extruding the gel formed through the heating process. In the method for producing silica glass by the step,

The sol filled in the extruder is formed by mixing fumed silica with deionized water and mixing and dispersing the dispersant, followed by mixing the silicon alkoxide having two alkoxide groups with the hydrolyzate hydrolyzed under a basic catalyst.

1 is a flow chart showing a method for producing silica glass by an extrusion process according to an embodiment of the present invention,

2 is a view for explaining the filling and heating process shown in FIG.

3 is a view for explaining the extrusion process shown in FIG.

4 is a perspective view showing a gel formed by an extrusion process according to an embodiment of the present invention,

5 is a view for explaining the filling and heating process for forming the over-jacketing tube,

6 is a view for explaining an extrusion process for forming the over-jacketing tube,

7 is a perspective view of a gel formed by an extrusion process for forming an overjacketing tube.

Hereinafter, with reference to the accompanying drawings will be described an embodiment of the present invention; In describing the present invention, detailed descriptions of related well-known functions or configurations are omitted in order not to obscure the subject matter of the present invention.

1 is a flow chart showing a method for producing silica glass by an extrusion process according to an embodiment of the present invention. The illustrated manufacturing method is a brush forming process 110, hydrolyzate forming process 120, mixing process 130, filling and heating process 140, extrusion process 150, drying process 160, low temperature heat treatment process 170 and the sintering process 180.

The sol forming process 110 is a process of forming a sol by mixing the fumed silica 111 and the dispersant 113 in deionized water (112). At this time, the pH value of the brush should be 11 or more. To satisfy these requirements. As the dispersant 113, an organic base is used. Prior to the technical problem of the present invention, the high dispersibility of the sole was heard, and the present invention is to improve the dispersibility of the sole by adjusting the pH value of the sole. Typically, in the case of making silica glass using fumed silica, the dispersed sol will have a high pH value. In other words, a uniformly dispersed sol is obtained using the charge on the particle surface of silica. When these soles contain the same concentration of silica, the higher the pH value, the higher the dispersibility. This phenomenon can also be seen through the zeta potential value of the silica particles. On the other hand, at low pH values of 10 or less, the dispersibility falls sharply. Therefore, when the concentration of silica in the sol is about 50 wt%, 25 wt% of tetramethylammonium hydroxide, a strong base material, is considered given the process convenience and dispersibility directly affecting the resulting silica glass. Dispersion using

The hydrolyzate formation process 120 is a process of hydrolysis by adding a basic catalyst 122 to the silicon alkoxide 121 having two alkoxide groups. The silicon alkoxide 121 having two alkoxide groups is a material having two alkoxide groups in a symmetrical position, and even under a basic catalyst, a uniform phase can be obtained without generating precipitates, and the amount of water required for hydrolysis is small. The amount of alcohol generated during hydrolysis is also reduced, which prevents cracking due to rapid volatilization of alcohol as well as improving the strength of the gel.

As the silicon alkoxide 121 having the two alkoxide groups, diethoxydiethylsilane or diethoxydiphenylsilane may be used. The present invention uses a basic catalyst in the hydrolyzate formation process (120). As the basic catalyst 122, ammonia water or the like is used.

The mixing process 130 is a process of mixing the hydrolyzate formed in the hydrolyzate forming process 120 with the brush generated in the brush forming process 110. Since the sol is a mixture of the hydrolyzate of the silicon alkoxide 121 having two alkoxide groups, the network or randomly branched polymer of the network structure is prevented to increase the strength of the gel. The gelling agent 141 may be added to the brush formed in the mixing process 130. The gelling agent 141 shortens the time required for the gel to gel. As the gelling agent 141, methyl lactate, ethyl lactate, or the like can be used. In addition, a bubble contained in the sole may be removed by using a vacuum pump or the like.

The filling and heating process 140 is a process of filling and heating the brush in the extruder. As the gelling agent is added, the gelation can be achieved in a few minutes in the heating process, which is advantageous for the continuous process.

2 is a view for explaining the filling and heating process 140 shown in FIG.

The extruder is a storage container 210 of a cylindrical form, which is a storage place of a brush, a removable piston 220 inserted into an upper end of the storage container 210 and a removable stopper 230 inserted into a lower end of the storage container 210. It is composed. The removable piston 220 is removed from the extruder and the removable stopper 230 is inserted into the storage container 210. Subsequently, the brush 240 formed in the mixing process 130 shown in FIG. 1 in the storage container 210 is placed in the storage container 210, and the piston 220 is placed on the upper end of the storage container 210 again. Insert it. Heat is applied to the heating zone of the extruder to gel the filled brush 240. In this case, the heating zone should be longer than the length of the gel to be extruded, the heating temperature is 100 ℃ or less boiling point of water, and a microwave resonator (heater) or the like is used as a heating means.

By this heating, the sol 240 is a polymerization reaction by the hydrolysis and condensation of silicon alkoxide having two alkoxide groups in the inside proceeds quickly, and eventually has a high strength.

Extrusion process 150 shown in Figure 1 is a process of extruding the gel formed in the filling and heating process 140.

3 is a view for explaining the extrusion process 150 shown in FIG. After the gel 250 is formed in the extruder by the filling and heating process 140, the piston 220 is pushed downward after removing the stopper 230 blocking the lower end of the extruder. Then, the gel 250 in the extruder is forced out of the extruder under the pressure of the piston 220.

Figure 4 is a perspective view showing a gel formed by the extrusion process according to an embodiment of the present invention. The rod-shaped gel 410 then constitutes a core portion of the optical fiber base material.

The drying process 160 shown in FIG. 1 is a process of drying the gel formed in the extrusion process 150 using a constant temperature and humidity chamber.

In the low temperature heat treatment process 170, the gel formed in the drying process 160 is heat treated while supplying gas such as chlorine, helium, hydrogen, oxygen, and the like to decompose organic matters such as residual moisture and binder in the gel. And alkali metal impurities and hydroxyl groups. The low temperature heat treatment process is a process of removing impurities in the gel as described above, and is also referred to as a purification process.

The sintering process 180 is a process of producing high purity silica glass to be finally obtained by sintering and vitrifying the gel after the low temperature heat treatment process 170 at a high temperature. The sintering process 180 is performed by heating the low-temperature heat-treated gel to about 1400 ℃ using a furnace (furnace) to move up and down in the sintering furnace in a helium (He) gas atmosphere. When the sintering process 180 is finished, high purity silica glass is obtained.

In the above-described embodiment, the process of forming the core of the optical fiber base material has been described, but a process of forming a substrate tube or an overjacketing tube of the optical fiber base material will be briefly described below.

5 is a view for explaining the filling and heating process for forming the over-jacketing tube. The extruder illustrated has a circular hole formed in the center of the stopper 530 in the extruder shown in FIG. 2, and has the same structure as the extruder of FIG. 2 except that the central rod 540 is inserted into the hole. The length at which the center rod 540 is inserted into the storage vessel 510 of the extruder should be at least longer than the length of the heating zone. The removable piston 520 is removed from the extruder and the removable stopper 530 is inserted into the storage container 510. Thereafter, the brush 550 formed in the mixing process in the storage container 510 is placed in the storage container 510, and the piston 520 is inserted again at the upper end of the storage container 510. The filled brush 550 is gelated by supplying heat to the heating zone of the extruder.

6 is a view for explaining an extrusion process for forming the over-jacketing tube. After the gel 560 is formed in the extruder by the filling and heating process described with reference to FIG. 5, the piston 520 is pushed downward after removing the stopper 530 blocking the lower end of the extruder. The gel 560 in the extruder then exits the extruder under pressure by the piston 520. At this time, the center rod 540 does not move at all in the initial position until the end of the extrusion process.

7 is a perspective view illustrating a gel formed by an extrusion process for forming an overjacketing tube. The tubular gel 710 then constitutes a cladding portion of the base material.

As described above, the method for producing silica glass by the extrusion process according to the present invention is excellent strength before drying and after drying of the gel by mixing a hydrolyzate composed of silicon alkoxide having two alkoxide groups hydrolyzed under basic catalyst to the sol. There is an advantage of implementing shrinkage characteristics.

Furthermore, the method for producing silica glass by the extrusion process according to the present invention has the advantage of improving the dispersibility of the brush by maintaining the pH value of the brush at 11 or more.

Claims (5)

In the manufacturing method of the silica glass by the extrusion process comprising a filling step of filling the brush in the extruder, a heating step of applying heat to the filled brush, and an extrusion step of extruding the gel formed through the heating step, The sol filled in the extruder is formed by mixing fumed silica with deionized water and dispersing with a dispersant, followed by mixing silicon alkoxide having two alkoxide groups with a hydrolyzate hydrolyzed under a basic catalyst. Method of making glass. The method of claim 1, The pH value of the sol is a method of producing silica glass by an extrusion process, characterized in that 11 or more. The method according to claim 1 or 2, The dispersing agent is a method for producing silica glass by an extrusion process, characterized in that the organic base. The method according to claim 1 or 2, The silicon alkoxide having two alkoxide groups is a method for producing silica glass by an extrusion process, characterized in that diethoxydiethylsilane or diethoxydiphenylsilane. The method according to claim 1 or 2, The basic catalyst is a silica glass production method by an extrusion process, characterized in that the use of ammonia water.