Porous glass substrate manufacturing system and glass substrate manufacturing method

Abstract

To provide a porous glass preform manufacturing system capable of stably supplying a raw material without requiring a manufacturing apparatus or a building responding to a hazardous material even when using an organic siloxane raw material as a raw material for forming silica particles.SOLUTION: A porous glass preform manufacturing system includes: a material supply device including a raw material tank having an organic siloxane raw material stored in a liquid state and a residual space filled with inert gas, a liquid sending pump for sending the organic siloxane raw material from the raw material tank, a circulation pipeline and branch pipeline for passing the sent organic siloxane raw material, a liquid mass flow controller for controlling the flow rate of the organic siloxane raw material passing through the branch pipeline to a predetermined flow rate and a vaporizer provided downstream from the liquid mass flow controller and for evaporating the organic siloxane raw material; and a porous glass preform manufacturing apparatus including a burner for burning the organic siloxane raw material evaporated by the vaporizer to form silica fine particles and placed in the indoor of a building. The material supply device is placed in the outdoor of the building or in the indoor of another building.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a porous glass base material manufacturing system including a raw material supply device and a porous glass base material manufacturing device, and a method for manufacturing a glass base material.

Background Art

[0002] Conventionally, a method for manufacturing a porous glass base material is known in which silica fine particles (SiO2 fine particles) are deposited on a starting base material such as a glass rod to form a soot. When this type of porous glass base material is dehydrated and sintered, a glass base material for manufacturing an optical fiber or the like can be obtained.

[0003] The porous glass base material is manufactured, for example, by externally depositing SiO2 fine particles by the OVD method or the like on a core base material manufactured by the VAD method or the like. As a silicon compound raw material for generating SiO2 fine particles, silicon tetrachloride (SiCl4) is widely used.

[0004] By supplying SiCl4 to a burner and subjecting it to flame hydrolysis, SiO2 fine particles are generated based on the following formula. SiCl4 + 2H2O → SiO2 + 4HCl

[0005] In this flame hydrolysis, hydrochloric acid is generated as a by-product. Therefore, when moisture is mixed in, it exhibits metal corrosiveness, so care must be taken in the manufacturing apparatus materials and exhaust temperature management. Although it is conceivable to provide equipment for recovering and treating hydrochloric acid from the exhaust, this leads to an increase in cost.

[0006] As a silicon compound raw material for generating SiO2 fine particles, a halogen-free organic silicon compound that does not contain Cl (chlorine) in the molecule may be used. As an example, octamethylcyclotetrasiloxane (OMCTS), which is a high-purity organic siloxane available on an industrial scale, can be mentioned.

[0007] When OMCTS is used, SiO2 fine particles are generated based on the following formula. [SiO(CH3)2]4+16O2→4SiO2+8CO2+12H2O Using halogen-free organic siloxanes, such as OMCTS, as silicon compound raw materials eliminates the emission of hydrochloric acid, thus increasing flexibility in handling manufacturing equipment materials and exhaust gases. Furthermore, the elimination of the need for hydrochloric acid recovery treatment facilities can be expected to reduce costs.

[0008] In addition, OMCTS has a very high heat of combustion, and it is expected that the amount of combustible gases such as hydrogen required for combustion will be reduced compared to when SiCl4 is used. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Patent No. 6793676 [Overview of the project] [Problems that the invention aims to solve]

[0010] OMCTS, an organic siloxane raw material, is a flammable liquid with a flash point of 54°C and falls under the category of Class 4, Group 2 petroleum hazardous materials under the Fire Service Act. Therefore, facilities that store or handle quantities exceeding the designated amount must be equipped to handle hazardous materials as stipulated by the Fire Service Act.

[0011] In the manufacturing apparatus for porous glass preforms for optical fibers described in Patent Document 1, a vaporizer for vaporizing the liquid raw material is installed inside the apparatus together with a burner for depositing silica microparticles. In other words, the raw material is supplied into the manufacturing apparatus in a liquid state. Therefore, the manufacturing apparatus and the building in which it is installed must be made hazardous materials compliant. Furthermore, drastic temperature fluctuations occur inside the manufacturing apparatus during the deposition of silica microparticles, which may lead to unstable supply and vaporization of the raw material liquid. In addition, the installation of a vaporizer inside the apparatus increases its size, resulting in the problem of increased space occupied within the building.

[0012] The object of the present invention is to provide a porous glass matrix manufacturing system and a method for manufacturing a glass matrix that does not require the manufacturing equipment or building to be made hazardous materials compliant, even when using organic siloxane raw materials as raw materials for producing silica nanoparticles, and that can provide a stable supply of raw materials. [Means for solving the problem]

[0013] The porous glass base material manufacturing system of the present invention comprises a raw material supply device comprising: a raw material tank in which liquid organic siloxane raw materials are stored and the remaining space is filled with inert gas; a liquid pump for supplying the organic siloxane raw materials from the raw material tank; circulation piping and branch piping for supplying the organic siloxane raw materials supplied by the liquid pump; a liquid mass flow controller for controlling the flow rate of the organic siloxane raw materials through the branch piping to a predetermined flow rate; a vaporizer provided downstream of the liquid mass flow controller for vaporizing the organic siloxane raw materials; and a porous glass base material manufacturing apparatus installed indoors in a building and equipped with a burner that burns the organic siloxane raw materials vaporized by the vaporizer to produce silica fine particles, wherein the raw material supply device is installed outdoors or indoors in another building.

[0014] A raw material liquid supply unit, equipped with a raw material tank and a liquid transfer pump, and a raw material vaporization unit, equipped with a liquid mass flow controller and a vaporizer, may be provided in separate buildings.

[0015] The raw material vaporization unit may be installed in one or more sets for a single porous glass base material manufacturing apparatus, and each set may be installed in a separate building.

[0016] The organic siloxane raw material may also be octamethylcyclotetrasiloxane (OMCTS).

[0017] The glass substrate manufacturing method of the present invention comprises the steps of manufacturing a porous glass substrate using the porous glass substrate manufacturing system of the present invention, and manufacturing a glass substrate by converting the porous glass substrate into transparent glass. [Effects of the Invention]

[0018] According to the porous glass base material manufacturing system and the glass base material manufacturing method of the present invention, even when an organic siloxane raw material is used as a raw material for generating silica fine particles, there is no need to make the manufacturing apparatus or the building compatible with dangerous substances, and a stable supply of raw materials becomes possible.

Brief Description of Drawings

[0019] [Figure 1] It is a figure which shows the structural example of the porous glass base material manufacturing system of this invention. [Figure 2] It is a figure which shows another structural example of the porous glass base material manufacturing system of this invention. [Figure 3] It is a figure which shows yet another structural example of the porous glass base material manufacturing system of this invention.

Embodiments for Carrying Out the Invention

[0020] Hereinafter, embodiments of the present invention will be described while referring to the drawings. In the following description and drawings, the same parts are denoted by the same reference numerals, and the parts once described will be omitted or described only as necessary.

[0021] FIG. 1 is a diagram showing a configuration example of a porous glass base material manufacturing system of the present invention. The porous glass base material manufacturing system of the present invention includes a raw material supply device and a porous glass base material manufacturing device 200. In FIG. 1, an example in which the number of installation tables of the porous glass base material manufacturing device 200 is three is shown, but the number of installation tables is arbitrary and may be one or a plurality of tables.

[0022] The raw material supply device includes a raw material tank 112, a circulation pipe 113, a liquid feed pump 114, a pressure loss part 115, a pressure reducing valve 131, a liquid mass flow controller 132, and a vaporizer 133. Among these, the raw material tank 112, the circulation pipe 113, the liquid feed pump 114, and the pressure loss part 115 constitute a raw material liquid supply part, and the pressure reducing valve 131, the liquid mass flow controller 132, and the vaporizer 133 constitute a raw material vaporization part. Further, a branch pipe 121 for feeding the raw material liquid 111 from the raw material liquid supply part to the raw material vaporization part is provided.

[0023] The raw material tank 112 stores the raw material liquid 111, and the remaining space is filled with an inert gas. The raw material liquid 111 is an organic siloxane raw material in liquid form. An example of an organic siloxane raw material is octamethylcyclotetrasiloxane (OMCTS).

[0024] To prevent excessive dissolution of inert gas in the raw material liquid 111 stored in the raw material tank 112, it is preferable to keep the internal pressure of the raw material tank 112 below 0.1 MPa, and even more preferable to keep it below 0.05 MPa.

[0025] The circulation piping 113 is a pipeline that starts from the raw material tank 112, circulates outside the raw material tank 112, and returns to the raw material tank 112. A liquid transfer pump 114 and a pressure loss section 115 are provided along the way. In addition, branch pipes 121 branching off from the circulation piping 113 are provided between the liquid transfer pump 114 and the pressure loss section 115. The number of branch pipes 121 is the same as the number of raw material vaporization units. Figure 1 shows an example where three raw material vaporization units are provided, in which case three branch pipes 121 are also provided.

[0026] The liquid transfer pump 114 discharges the raw material liquid 111 supplied from the raw material tank 112 and sends it to the circulation pipe 113. The circulation pipe 113 circulates the raw material liquid 111 and also sends the raw material liquid 111 to the branch pipe 121.

[0027] The discharge pressure of the raw material liquid 111 from the liquid transfer pump 114 is preferably equal to or greater than the internal pressure of the raw material tank 112 in order to prevent the generation of bubbles due to inert gas dissolved in the raw material liquid 111. Specifically, it is preferable that the discharge pressure be 0.2 to 0.7 MPa, and more preferably 0.4 to 0.6 MPa.

[0028] The capacities of the raw material tank 112, circulation piping 113, and liquid transfer pump 114 are determined by the total amount of raw material liquid 111 used.

[0029] The pressure loss section 115 is an orifice or the like, and is located downstream of the discharge of the liquid transfer pump 114 and downstream of the branching point of the branch piping 121, and maintains the discharge pressure of the raw material liquid 111 at a predetermined pressure.

[0030] The raw material liquid 111, which is sent from the circulation pipe 113 to the branch pipe 121, is supplied to the raw material vaporization section. The raw material vaporization section is equipped with a pressure reducing valve 131, a liquid mass flow controller 132, and a vaporizer 133, in that order from the upstream side.

[0031] The raw material liquid 111 supplied to the raw material vaporization section is reduced in pressure to, for example, 0.2 to 0.5 MPa by the pressure reducing valve 131, then its flow rate is controlled to a predetermined flow rate by the liquid mass flow controller 132, and finally vaporized in the vaporizer 133.

[0032] In the vaporizer 133, the raw material liquid 111 can be efficiently vaporized by mixing it with a carrier gas. Examples of carrier gases include inert gases such as nitrogen, argon, and helium, oxygen, or a mixture of oxygen and an inert gas. The carrier gas may be preheated according to its supply flow rate in order to efficiently vaporize the raw material liquid 111 in the vaporizer 133. Furthermore, when OMCTS is used as the organic siloxane raw material, the temperature inside the vaporizer 133 is preferably set to 150-250°C from the viewpoint of efficiently vaporizing the raw material liquid 111 and preventing polymerization of the raw material substances.

[0033] The raw material gas obtained by vaporizing the raw material liquid 111 is sent to the raw material gas piping 141 and supplied to the burner 201 of the porous glass base material manufacturing apparatus 200.

[0034] The porous glass base material manufacturing apparatus 200 generates silica fine particles (SiO2 fine particles) by burning a raw material gas in a burner 201, and deposits these particles onto a starting base material such as a glass rod to manufacture a porous glass base material.

[0035] Although Figure 1 shows an example where a porous glass base material manufacturing apparatus 200 and a raw material vaporization unit are provided in a one-to-one ratio, the apparatus may also be configured so that raw material gas is supplied to a single porous glass base material manufacturing apparatus 200 from multiple sets of raw material vaporization units, depending on the required supply flow rate of raw material gas.

[0036] In this invention, the raw material supply device and the porous glass base material manufacturing device 200 are installed in separate spaces. For example, as shown in Figure 1, the raw material supply device may be installed indoors in building 10, and the porous glass base material manufacturing device 200 may be installed indoors in building 20, which is separate from building 10. Alternatively, either the raw material supply device or the porous glass base material manufacturing device 200 may be installed indoors in a building, and the other outdoors.

[0037] When OMCTS is used as an organic siloxane raw material, the freezing point of OMCTS is 17°C and the flash point is 54°C. Therefore, in order to prevent OMCTS from freezing, it is preferable to maintain the indoor temperature of building 10 where the raw material supply equipment is installed at approximately 30°C, or to keep each piece of equipment and each pipe at approximately 30°C using electricity, steam, hot water, etc.

[0038] By installing the raw material supply device and the porous glass base material manufacturing device 200 in separate spaces, the space handling liquid raw materials is isolated from the space where the porous glass base material manufacturing device 200, equipped with a burner 201, is installed. This eliminates the need to make the porous glass base material manufacturing device 200 or the building in which it is installed hazardous materials compliant. Furthermore, by installing the vaporizer 133 outside the porous glass base material manufacturing device 200, it is possible to avoid increasing the size of the porous glass base material manufacturing device 200.

[0039] Furthermore, by installing the raw material vaporization equipment in a separate space unaffected by temperature changes in the porous glass base material manufacturing apparatus 200, the supply of raw materials can be stabilized. For example, if the temperature inside the liquid mass flow controller 132 rises relative to the raw material tank 112, any gas dissolved in the raw material liquid 111 that exceeds the saturation dissolution amount may be generated as bubbles inside the liquid mass flow controller 132, potentially hindering the supply and vaporization of the raw material liquid. However, according to the configuration in Figure 1, the liquid mass flow controller 132 is installed indoors in a building 10 separate from the building 20 where the porous glass base material manufacturing apparatus 200 is installed, and the raw material tank 112 is also installed indoors in the same building 10. This eliminates the difference in ambient temperature, thus avoiding the occurrence of this problem and stabilizing the supply of raw materials.

[0040] A glass base material can be manufactured by performing the following steps: manufacturing a porous glass base material using the porous glass base material manufacturing system configured as described above, and dehydrating and sintering the manufactured porous glass base material to convert it into transparent glass by heating it at approximately 1500°C in, for example, a helium gas-containing atmosphere.

[0041] <Example 1> Instead of installing the raw material supply equipment together in one building 10, the raw material liquid supply unit and the raw material vaporization unit may be installed in separate buildings 11 and 12, as shown in Figure 2.

[0042] Even in the configuration shown in Figure 2, it is preferable to maintain the indoor temperature at approximately 30°C in both building 11 and building 12, or to keep the temperature of each installed piece of equipment and piping at approximately 30°C. This prevents the solidification of OMCTS and ensures a stable supply of raw materials.

[0043] In addition, either the raw material liquid supply unit or the raw material vaporization unit may be installed outdoors.

[0044] <Modification 2> When there are multiple raw material vaporization units, instead of installing them all together in one building 12, they may be installed in separate buildings, as shown in Figure 3. In Figure 3, there are three raw material vaporization units, so they are installed in buildings 12a, 12b, and 12c, respectively.

[0045] In the configuration shown in Figure 3, it is preferable to maintain the indoor temperature at approximately 30°C in each of buildings 12a, 12b, and 12c, or to keep the temperature of each installed piece of equipment and piping at approximately 30°C. This prevents the solidification of OMCTS and ensures a stable supply of raw materials.

[0046] The present invention is not limited to the embodiments described above. The embodiments described above are illustrative, and any configuration that is substantially identical to the technical idea described in the claims of the present invention and produces similar effects is included within the technical scope of the present invention. In other words, modifications can be made as appropriate within the scope of the technical idea expressed in the present invention, and such modified or improved forms are also included within the technical scope of the present invention. [Explanation of Symbols]

[0047] 10, 11, 12, 12a, 12b, 12c, 20 buildings 111 Raw material liquid 112 Raw material tanks 113 Circulation piping 114 Liquid transfer pump 115 Pressure loss section 121 Branch piping 131 Pressure Reducing Valve 132 Liquid Mass Flow Controller 133 Vaporizer 141 Raw gas piping 200 Porous glass substrate manufacturing apparatus 201 burner

Claims

1. A raw material tank in which liquid organic siloxane raw materials are stored, with the remaining space filled with inert gas, A liquid transfer pump for transferring the organic siloxane raw material from the raw material tank, A circulation pipe and branch pipe through which the organic siloxane raw material, which is supplied by the aforementioned liquid transfer pump, A liquid mass flow controller that controls the flow rate of the organic siloxane raw material through the branched piping to a predetermined flow rate, A vaporizer is provided downstream of the liquid mass flow controller to vaporize the organic siloxane raw material, A raw material supply device equipped with, A porous glass base material manufacturing apparatus is installed inside a building and includes a burner that burns the organic siloxane raw material vaporized by the vaporizer to produce silica fine particles, Equipped with, The raw material supply device is installed inside a building separate from the building, which is not affected by the temperature changes of the porous glass base material manufacturing apparatus, and the room temperature inside the building not affected by the temperature changes of the porous glass base material manufacturing apparatus is maintained at 30°C in the porous glass base material manufacturing system.

2. A porous glass base material manufacturing system according to claim 1, wherein a raw material liquid supply unit comprising the raw material tank and the liquid transfer pump, and a raw material vaporization unit comprising the liquid mass flow controller and the vaporizer are provided in separate buildings, and the indoor temperature of both the building of the raw material liquid supply unit and the building of the raw material vaporization unit is maintained at 30°C.

3. The porous glass base material manufacturing system according to claim 2, wherein one or more sets of raw material vaporization units are installed in one porous glass base material manufacturing apparatus, each set is installed in a separate building, and the indoor temperature of each set's building is maintained at 30°C.

4. The porous glass matrix manufacturing system according to any one of claims 1 to 3, wherein the organic siloxane raw material is octamethylcyclotetrasiloxane (OMCTS).

5. A step of manufacturing a porous glass base material using the porous glass base material manufacturing system described in claim 1, The steps include: manufacturing a glass base material by converting the porous glass base material into transparent glass; A method for manufacturing a glass base material.

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