JP6408378B2 - Manufacturing method of glass substrate - Google Patents

Description

  The present invention relates to a method for manufacturing a glass substrate.

  In order to manufacture a glass substrate (hereinafter referred to as “glass substrate for display”) used in a flat panel display such as a liquid crystal display or a plasma display, an overflow down draw method may be used (see, for example, Patent Document 1). The overflow down-draw method includes a step of forming a sheet-like sheet glass below the formed body by causing the molten glass to overflow (overflow) from the upper portion of the formed body in a forming furnace, and a cooling step of gradually cooling the sheet glass in an annealing furnace. Including. In the slow cooling furnace, the sheet glass is drawn between a pair of rollers, and the sheet glass is stretched to a desired thickness while being conveyed downward by the roller, and then the sheet glass is gradually cooled. Thereafter, the glass sheet is formed by cutting the sheet glass into a predetermined dimension.

Japanese Patent No. 5246568

  In the sheet glass manufactured by the overflow down draw method, there may be a streak region (stria) having a refractive index and specific gravity different from those of the surroundings. One cause of striae is uneven composition of the molten glass. In the process upstream of the molded body, a heterogeneous substrate having a composition different from that of the surroundings may be generated in the molten glass. As a factor for generating a heterogeneous substrate, impurities such as zirconia are eluted from the wall surface and bottom surface of the melting tank for melting the glass raw material into the molten glass, the composition changes, and a clarification tank for removing bubbles from the molten glass, In a processing apparatus such as an agitation tank that stirs molten glass, it is conceivable that the composition changes due to volatilization of volatile components such as boron in the molten glass in the gas phase space.

  In addition, when glass with a higher viscosity than the surroundings is produced in the molten glass and this high viscosity glass adheres to the molded body, wide striae (surface irregularities) are formed in the width direction of the sheet glass. There is also.

  An object of this invention is to provide the manufacturing method of the glass substrate which specifies the cause of the surface unevenness | corrugation produced | generated by sheet glass, and can reduce the production | generation of surface unevenness | corrugation by eliminating this cause.

A first aspect of the present invention is a method for manufacturing a glass substrate,
A molding step of forming a sheet glass by molding a molten glass supplied from a molten glass processing apparatus by a molding apparatus;
A detection step of detecting the unevenness amount of the surface unevenness generated in the conveying direction of the sheet glass;
When an unevenness amount larger than a predetermined reference value is detected, an analysis step for analyzing the composition of the sheet glass;
Based on the analyzed composition, in the processing apparatus or the molding apparatus, a specific step of identifying the occurrence position of the cause of the surface irregularities,
And a elimination step of eliminating the cause at the generation position and reducing the generation of the surface irregularities.

In the identifying step, identify the occurrence position of the heterogeneous substrate having a composition different from the surrounding in the molten glass, which causes surface irregularities,
In the eliminating step, it is preferable that the molten glass at the generation position is discharged from the processing apparatus.

The processing apparatus has a space in which the molten glass is accommodated therein, and a gas phase space above the molten glass, and an upper discharge port for discharging the molten glass facing the gas phase space,
In the analysis step, the content of silica in the sheet glass is analyzed,
When the silica content in the surface irregularity region is larger than the silica content in the other region, the location facing the gas phase space is identified as the occurrence position of the heterogeneous base in the identifying step, and the elimination step It is preferable that the molten glass facing the gas phase space is discharged from the upper discharge port.

  It is preferable that the discharge of the molten glass from the upper discharge port is stopped when the content of silica in the molten glass discharged from the upper discharge port becomes a predetermined reference value or less.

The processing apparatus has a space in which molten glass is accommodated therein, and a lower discharge port for discharging the molten glass at the bottom,
In the analysis step, the content of zirconia in the sheet glass is analyzed,
When the content of zirconia in the region of the surface unevenness is larger than a predetermined reference value in the content of zirconia in the other region, the bottom of the processing device is specified as the occurrence position of the heterogeneous base in the specifying step, In the eliminating step, it is preferable that the molten glass facing the bottom of the processing apparatus is discharged from the lower discharge port.

  It is preferable that the discharge of the molten glass from the lower outlet is stopped when the content of zirconia in the molten glass discharged from the lower outlet becomes a predetermined reference value or less.

In the analysis step, the content of silica and zirconia in the sheet glass is analyzed,
When the content of silica and the content of zirconia is below a predetermined reference value, in the specific step, the glass adhering to the molded body for forming the sheet glass from the molten glass is identified as the cause of surface irregularities,
In the elimination step, it is preferable to increase the temperature of the molded body.

  According to the method for manufacturing a glass plate of the above-described aspect, when a concavo-convex amount larger than a predetermined reference value is detected, the composition of the sheet glass is analyzed, and based on the analyzed composition, in the processing apparatus or the molding apparatus The generation position of the surface unevenness can be reduced by specifying the occurrence position of the surface unevenness and eliminating the cause at the generation position.

It is a figure which shows the flow of the manufacturing method of this embodiment. It is the schematic of the manufacturing apparatus of a glass substrate.

Hereinafter, the manufacturing method of the glass substrate of this invention is demonstrated.
(Overall overview of glass substrate manufacturing method)
Drawing 1 is a figure showing an example of a process of a manufacturing method of a glass substrate of this embodiment. The glass substrate manufacturing method includes a melting step (ST1), a clarification step (ST2), a homogenization step (ST3), a supply step (ST4), a molding step (ST5), a slow cooling step (ST6), and a detection step (ST7). And a cutting step (ST8). In addition, a grinding process, a polishing process, a cleaning process, an inspection process, a packing process, and the like may be included. The manufactured glass substrate is laminated in a packing process as necessary, and is transported to a supplier.

In the melting step (ST1), molten glass is made by heating the glass raw material.
In the clarification step (ST2), when the molten glass is heated, bubbles containing oxygen, CO ₂ or SO ₂ contained in the molten glass are generated. This bubble grows by absorbing oxygen generated by the reduction reaction of the clarifying agent (tin oxide or the like) contained in the molten glass, and floats on the liquid surface of the molten glass and is released. Thereafter, in the clarification step, by reducing the temperature of the molten glass, the reducing substance obtained by the reduction reaction of the clarifier undergoes an oxidation reaction. Thereby, gas components, such as oxygen in the bubble which remain | survives in molten glass, are reabsorbed in molten glass, and a bubble lose | disappears.

In the homogenization step (ST3), the glass component is homogenized by stirring the molten glass using a stirrer. Thereby, the composition unevenness of the glass which is a cause of striae or the like can be reduced. A homogenization process is performed in the stirring tank mentioned later.
In the supplying step (ST4), the stirred molten glass is supplied to the molding apparatus.

The molding step (ST5) and the slow cooling step (ST6) are performed by a molding apparatus.
In the forming step (ST5), the molten glass is formed into a sheet glass to make a flow of the sheet glass. An overflow downdraw method is used for molding.
In the slow cooling step (ST6), the sheet glass that has been formed and flowed is cooled to a desired thickness, so that internal distortion does not occur and warpage does not occur.
In the detection step (ST7), the presence or absence of surface unevenness of the sheet glass after slow cooling, the position in the width direction of the surface unevenness, and the unevenness amount of the surface unevenness (the amount of depression or protrusion from the reference surface) are detected.
In the cutting step (ST8), the sheet glass after slow cooling is cut into a predetermined length to obtain a plate-like glass substrate. The cut glass substrate is further cut into a predetermined size to produce a glass substrate having a target size.

  FIG. 2 is a schematic view of a glass substrate manufacturing apparatus that performs the melting step (ST1) to the cutting step (ST8) in the present embodiment. As shown in FIG. 2, the glass substrate manufacturing apparatus mainly includes a melting apparatus 100, a forming apparatus 200, and a cutting apparatus 300. The melting apparatus 100 includes a melting tank 101, a clarification tube 102, a stirring device 130, transfer tubes 104 and 105, and a glass supply tube 106.

The melting tank 101 shown in FIG. 2 is provided with heating means such as a burner (not shown). A glass raw material to which a clarifying agent is added is charged into the melting tank, and a melting step (ST1) is performed. The molten glass melted in the melting tank 101 is supplied to the clarification tube 102 via the transfer tube 104.
In the clarification tube 102, the temperature of the molten glass MG is adjusted, and the clarification step (ST2) of the molten glass is performed using the oxidation-reduction reaction of the clarifier. Specifically, when the molten glass in the clarification tube 102 is heated, the bubbles containing oxygen, CO ₂ or SO ₂ contained in the molten glass absorb oxygen generated by the reductive reaction of the clarifier. It grows and floats on the liquid surface of the molten glass and is released into the gas phase space. Thereafter, by reducing the temperature of the molten glass, the reducing substance obtained by the reductive reaction of the fining agent undergoes an oxidation reaction. Thereby, gas components, such as oxygen in the bubble which remain | survives in molten glass, are reabsorbed in molten glass, and a bubble lose | disappears. The clarified molten glass is supplied to the stirring device 130 via the transfer pipe 105.

  In the stirring device 130, the molten glass is stirred and a homogenization step (ST3) is performed. The stirring device 130 includes a first stirring tank 130A, a second stirring tank 130B, a first stirring bar 131A, a second stirring bar 131B, a lower discharge port 132A, an upper discharge port 132B, a transfer pipe 133, Have The molten glass is homogenized by stirring in the first stirring tank 130A and the second stirring tank 130B.

Molten glass is supplied to the first stirring tank 130 </ b> A from below by the transfer pipe 105. The molten glass rises in the first stirring tank 130A while being stirred by the first stirring bar 131A. The molten glass that has reached the upper part of the first stirring tank 130 </ b> A is transferred to the upper part of the second stirring tank by the transfer pipe 133.
In the processing apparatus such as the melting tank 101 and the clarification tube 102, impurities having a large specific gravity such as zirconia are eluted from the wall surface of the processing apparatus into the molten glass, the composition changes, and the composition is different from the surroundings in the molten glass. A substrate may be generated. Such a heterogeneous substrate has a large specific gravity and therefore tends to accumulate at the bottom of the first stirring tank 130A. A lower discharge port 132A is provided at the bottom of the first stirring tank 130A. By opening the lower discharge port 132A, molten glass containing a heterogeneous base material having a large specific gravity accumulated at the bottom of the first stirring tank 130A is externally provided. Can be discharged.

Molten glass is supplied to the second stirring tank 130 </ b> B from above by the transfer pipe 133. The molten glass descends in the second stirring tank 130B while being stirred by the second stirring bar 131B. The molten glass that has reached the lower portion of the second stirring tank 130 </ b> B is transferred to the molded body 210 of the molding apparatus 200 through the glass supply pipe 106.
In the processing apparatus such as the melting tank 101, the clarification tube 102, and the stirring apparatus 130, the composition of the molten glass changes due to volatilization of volatile components such as boron from the surface facing the gas phase space of the molten glass, and the relative In particular, a heterogeneous substrate having a high silica ratio and a low specific gravity may be generated. Such a heterogeneous substrate having a small specific gravity tends to accumulate in an upper portion facing the gas phase space of the second stirring tank 130B. An upper discharge port 132B is provided in the upper part of the second stirring tank 130B. By opening the upper discharge port 132B, molten glass containing a heterogeneous base material having a small specific gravity accumulated in the upper part of the second stirring tank 130B is externally provided. Can be discharged.

The molten glass homogenized by the stirring device 130 is supplied to the molding device 200 through the glass supply pipe 106 (supply step ST4).
In the molding apparatus 200, the sheet glass SG is molded from the molten glass flowing down from the molded body 210 by the overflow down draw method (molding step ST5) and gradually cooled (slow cooling step ST6).
In addition, when glass with higher viscosity than the surroundings is contained in the molten glass, when this highly viscous glass adheres to the molded body 210, a wide striae (surface irregularities) is formed in the width direction of the sheet glass. There is a risk of formation. When the temperature of the molded body 210 is raised, the viscosity of the molten glass adhering to the molded body 210 can be reduced, and the highly viscous glass adhering to the molded body 210 can be removed. Here, when the temperature of the molded body 210 is too high, there is a problem that a burden on the molded body 210 and the molding apparatus 200 increases. For this reason, it is preferable that the maximum temperature of the molded object 210 shall be 1400 degrees C or less.

In the detection apparatus 290 in the shaping | molding apparatus 200, surface unevenness | corrugation is detected with respect to the sheet glass SG after slow cooling (detection process ST7).
The detection device 290 is, for example, an optical surface inspection device, and the position in the width direction of the surface unevenness generated in the sheet glass SG carried out from the lower part of the slow cooling furnace 202, the amount of surface unevenness (the amount of recesses from the reference surface). (Or protrusion amount). In addition, this recessed part and convex part are the things from which the thickness (height) of the sheet glass SG was fluctuate | varied, and generate | occur | produces continuously in the streak form in the conveyance direction of the sheet glass SG.

  The analyzing device 291 in the forming device 200 analyzes the composition of the sheet glass SG. As the analyzer 291, for example, an electron probe microanalyzer (EPMA) or a time-of-flight secondary ion mass spectrometer (TOF-SIMS) can be used.

  In the cutting device 300, a plate-shaped glass substrate cut out from the sheet glass SG is formed (cutting step ST8).

In the present embodiment, in the detection step, when a concavo-convex amount larger than a predetermined reference value is detected, the composition of the sheet glass is analyzed using the analysis device 291, and the processing device or A process for reducing the generation of surface irregularities is performed by identifying the occurrence position of the cause of the surface irregularities in the molding apparatus and eliminating the cause at the occurrence position.
Specifically, by comparing the difference in composition and segregation between the region where the surface irregularities are formed and the region where the surface irregularities are not formed, the components contained in the heterogeneous substrate that causes the surface irregularities are increased. Identify.

  For example, when it is analyzed that the content of zirconia is higher in the region where the surface unevenness is not formed than in the region where the surface unevenness is not formed, in the processing device such as the melting tank 101 and the clarification tube 102, It can be determined that zirconia eluted from the wall surface into the molten glass, and a heterogeneous substrate having a high zirconia content was generated. In this case, the heterogeneous substrate having a high zirconia content has a larger specific gravity than the other portions of the molten glass, and therefore, it is considered that the heterogeneous substrate accumulates at the bottom of the first stirring tank 130A. Therefore, as a process for reducing the generation of surface irregularities, the lower discharge port 132A of the stirring device 130 is opened, and the molten glass containing a heterogeneous substrate having a large specific gravity accumulated at the bottom of the first stirring tank 130A is discharged to the outside. Thereby, the surface unevenness | corrugation resulting from the heterogeneous base material with large specific gravity can be reduced.

  When the molten glass containing the heterogeneous substrate having a large specific gravity is discharged from the bottom of the first stirring tank 130A, the discharge of the molten glass from the lower discharge port 132A is stopped. For example, the component of the molten glass discharged from the lower discharge port 132A is analyzed, and when the content of zirconia in the molten glass discharged from the lower discharge port 132A becomes a predetermined reference value or less, the lower discharge port 132A What is necessary is just to stop discharge | emission of molten glass. Alternatively, the lower discharge port 132A may be opened for a certain period of time and the lower discharge port 132A may be closed after a predetermined amount of molten glass has been discharged.

  Further, for example, when it is analyzed that the content of silica is higher in the region where the surface unevenness is not formed than in the region where the surface unevenness is not formed, the processing of the melting tank 101, the clarification tube 102, the stirring device 130, etc. In the apparatus, it can be determined that the composition of the molten glass is changed by volatilization of a volatile component such as boron from the surface of the molten glass into the gas phase space, and a heterogeneous substrate having a high silica content is generated. In this case, the heterogeneous substrate having a high silica content has a smaller specific gravity than the other portions of the molten glass, and therefore, it is considered that the heterogeneous substrate accumulates in the upper part of the second stirring tank 130B. Therefore, as a process for reducing the generation of surface irregularities, the upper discharge port 132B of the stirring device 130 is opened, and the molten glass containing a heterogeneous substrate having a small specific gravity accumulated in the upper portion of the second stirring tank 130B is discharged to the outside. Thereby, the surface unevenness | corrugation resulting from the heterogeneous substrate with small specific gravity can be reduced.

  When the molten glass containing the heterogeneous substrate having a small specific gravity is discharged from the upper part of the second stirring tank 130B, the discharge of the molten glass from the upper discharge port 132B is stopped. For example, the composition of the molten glass discharged from the upper outlet 132B is analyzed, and when the content of silica in the molten glass discharged from the upper outlet 132B becomes a predetermined reference value or less, the upper outlet 132B What is necessary is just to stop discharge | emission of molten glass. Alternatively, the upper outlet 132B may be opened for a certain period of time and the upper outlet 132B may be closed after a predetermined amount of molten glass has been discharged.

  Further, for example, when there is no difference in the composition (for example, silica, zirconium, etc.) between the region where the surface unevenness is not formed and the region where the surface unevenness is not formed, the surface unevenness is not a heterogeneous substrate, and the molded body 210. It can be determined that this is due to the highly viscous glass adhering to the glass. In this case, by increasing the temperature of the molded body 210, the viscosity of the molten glass attached to the molded body 210 can be reduced, and the highly viscous glass attached to the molded body 210 can be removed.

  As described above, according to the present embodiment, when a concavo-convex amount larger than a predetermined reference value is detected, the composition of the sheet glass is analyzed, and based on the analyzed composition, in the processing apparatus or the molding apparatus, By identifying the occurrence position of the cause of the surface unevenness and eliminating the cause at the occurrence position, the generation of the surface unevenness can be reduced.

  As mentioned above, although the manufacturing method of the glass substrate of this invention was demonstrated in detail, this invention is not limited to the said embodiment, In the range which does not deviate from the main point of this invention, you may make various improvement and a change. Of course. In the said embodiment, although the example which pinpoints the generation | occurrence | production position of the cause of surface unevenness based on content of the silica and zirconium in molten glass was demonstrated, this invention is not limited to this, Other components in molten glass The occurrence position of the cause of surface irregularities may be specified based on the content of.

  Although the case where the lower discharge port 132A and the upper discharge port 132B are provided in the stirring device 130 has been described in the above embodiment, the present invention is not limited to this. For example, the melting tank 101 may be provided with a lower outlet and an upper outlet, and the clarification tank 102 may be provided with a lower outlet and an upper outlet.

  For the glass substrate produced by the method for producing a glass substrate of the present embodiment, an alkali-free boroaluminosilicate glass having a high strain point and a slow cooling point and good dimensional stability or a glass containing a trace amount of alkali is used.

The glass substrate to which this embodiment is applied is made of an alkali-free glass having the following composition, for example.
SiO _2: 56-65% by weight
Al ₂ O ₃ : 15-19% by mass
B ₂ O _3: 8-13 wt%
MgO: 1-3% by mass
CaO: 4-7% by mass
SrO: 1-4% by mass
BaO: 0-2 mass%
Na ₂ O: 0-1% by mass
K ₂ O: 0-1 wt%
As ₂ O ₃ : 0-1% by mass
Sb ₂ O _3: 0-1 wt%
SnO ₂ : 0-1% by mass
Fe ₂ O ₃ : 0-1% by mass
ZrO ₂ : 0-1% by mass

The glass substrate manufactured by this embodiment is suitable for the glass substrate for a display containing the glass substrate for flat panel displays. It is suitable for an oxide semiconductor display glass substrate using an oxide semiconductor such as IGZO (indium, gallium, zinc, oxygen) and an LTPS display glass substrate using an LTPS (low temperature polysilicon) semiconductor. Moreover, the glass substrate manufactured by this embodiment is suitable for the glass substrate for liquid crystal displays by which it is calculated | required that content of an alkali metal oxide is very small. Moreover, it is suitable also for the glass substrate for organic EL displays. In other words, the manufacturing method of the glass substrate of this embodiment is suitable for manufacture of the glass substrate for displays, and is especially suitable for manufacture of the glass substrate for liquid crystal displays.
Moreover, the glass substrate manufactured by this embodiment is applicable also to a cover glass, the glass for magnetic discs, the glass substrate for solar cells, etc.

DESCRIPTION OF SYMBOLS 100 Melting apparatus 101 Melting tank 102 Clarification tank 104,105 Transfer pipe 106 Glass supply pipe 130 Stirrer 130A, 130B Stirrer tank 131A, 131B Stirrer 132A Lower discharge port 132B Upper discharge port 133 Transfer pipe 200 Molding device 210 Molded body 290 Detection Device 291 Analyzing device 300 Cutting device

Claims (7)

A method of manufacturing a glass substrate,
A molding step of forming a sheet glass by molding a molten glass supplied from a molten glass processing apparatus by a molding apparatus;
A detection step of detecting the unevenness amount of the surface unevenness generated in the conveying direction of the sheet glass;
When an unevenness amount larger than a predetermined reference value is detected, an analysis step for analyzing the composition of the sheet glass;
Based on the analyzed composition, in the processing apparatus or the molding apparatus, a specific step of identifying the occurrence position of the cause of the surface irregularities,
And a elimination step of eliminating the cause and reducing the generation of the surface irregularities at the generation position. In the identifying step, identify the occurrence position of the heterogeneous substrate having a composition different from the surrounding in the molten glass, which causes surface irregularities,
The manufacturing method of the glass substrate of Claim 1 which discharges | emits the molten glass of the said generation | occurrence | production position from the said processing apparatus in the said cancellation process. The processing apparatus has a space in which the molten glass is accommodated therein, and a gas phase space above the molten glass, and an upper discharge port for discharging the molten glass facing the gas phase space,
In the analysis step, the content of silica in the sheet glass is analyzed,
When the silica content in the surface irregularity region is larger than the silica content in the other region, the location facing the gas phase space is identified as the occurrence position of the heterogeneous base in the identifying step, and the elimination step The method for producing a glass substrate according to claim 2, wherein the molten glass facing the gas phase space is discharged from the upper discharge port.   The glass substrate according to claim 3, wherein the discharge of the molten glass from the upper discharge port is stopped when the content of silica in the molten glass discharged from the upper discharge port becomes a predetermined reference value or less. Production method. The processing apparatus has a space in which molten glass is accommodated therein, and a lower discharge port for discharging the molten glass at the bottom,
In the analysis step, the content of zirconia in the sheet glass is analyzed,
When the content of zirconia in the region of the surface unevenness is larger than a predetermined reference value in the content of zirconia in the other region, the bottom of the processing device is specified as the occurrence position of the heterogeneous base in the specifying step, The manufacturing method of the glass substrate as described in any one of Claims 2-4 which discharges | emits the molten glass which faces the bottom part of the said processing apparatus from the said lower discharge port in a cancellation | release process.   The glass substrate according to claim 5, wherein the discharge of the molten glass from the lower discharge port is stopped when the content of zirconia in the molten glass discharged from the lower discharge port becomes a predetermined reference value or less. Production method. In the analysis step, the content of silica and zirconia in the sheet glass is analyzed,
When the content of silica and the content of zirconia is below a predetermined reference value, in the specific step, the glass adhering to the molded body for forming the sheet glass from the molten glass is identified as the cause of surface irregularities,
The manufacturing method of the glass substrate as described in any one of Claims 1-6 which raises the temperature of the said molded object in the said cancellation process.

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