JP2017181446A - Moisture content measuring method of glass substrate, and manufacturing method of glass substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a measuring method of accurately measuring a β-OH value for moisture content measurement of a glass substrate, and to provide a glass substrate manufacturing method of stably manufacturing a glass substrate having a small thermal contraction amount, while suppressing the fluctuation in thermal shrinkage occurring in a manufacturing process by accurately controlling the β-OH value of the glass substrate in the manufacturing process.SOLUTION: In a moisture content measuring method of a glass substrate by measurement of a β-OH value, a coating layer that has a refractive index equivalent to that of the glass substrate and is made of a component containing no material having a hydroxyl group is formed on a principal surface of the glass substrate, which is an object of the moisture content measurement. The moisture content of the glass substrate having the coating layer is measured using an IR (infrared spectroscopic analysis).SELECTED DRAWING: Figure 3

Description

  The present invention relates to a method for measuring a moisture content of a glass substrate and a method for producing a glass substrate including a moisture content measuring step.

  In the production of glass plates, if a raw material with a high water content (for example, a hydroxide raw material) is used as the glass raw material, or if oxygen combustion heating with high combustion efficiency is performed in the melting step of the glass raw material, the amount of water dissolved in the glass is reduced. To increase. In particular, in the production of a glass substrate for a flat panel display, moisture contained in the glass affects the quality of the glass substrate.

  In the field of display panels in recent years, high definition of pixels has progressed to improve image quality, and the glass does not easily change its dimensions even when the glass substrate is heat-treated at a high temperature during the manufacturing process of the display panel. There is a need for a substrate.

  In general, thermal contraction of a glass substrate is suppressed by increasing a characteristic temperature (hereinafter, abbreviated as a low temperature viscosity characteristic temperature) in a low temperature viscosity region typified by a strain point or Tg (glass transition point) of the glass substrate. . On the other hand, when the low temperature viscosity characteristic temperature is increased, the meltability of the glass is lowered. When the moisture content of the glass is reduced, the thermal shrinkage rate during display production tends to be reduced, and in order to achieve both a low shrinkage rate and meltability, the β-OH value, which is an indicator of the moisture content of the glass, is adjusted to be small. It is known (Patent Document 1).

JP2015-231942A

  Conventionally, in the measurement of water content in glass, to measure the hydroxyl content in glass, β-OH is measured by IR spectroscopy, and the water content in glass is estimated by measuring β-OH. As an indicator.

  In the production of glass substrates for flat panel displays, in order to produce a glass substrate with a low thermal shrinkage rate, and to prevent the glass substrate quality from deteriorating due to the amount of moisture in the glass, the glass substrate production process The glass substrate after forming and cooling is periodically sampled, the β-OH value of the formed glass substrate is measured, the raw materials are mixed, the conditions for melting and heating, and the platinum used in the molten glass processing step It is necessary to properly manage the atmospheric conditions outside the equipment.

  However, in the measurement of the β-OH value of the glass substrate, the infrared absorption spectrum may not be constant, and in order to optimally manage the production of the glass substrate for the flat panel display, the β-OH value is measured. It was necessary to improve the accuracy of

  The present invention provides a measuring method for measuring the β-OH value with high accuracy for measuring the moisture content of the glass substrate, and also accurately manages the β-OH value of the glass substrate in the manufacturing process, thereby providing a manufacturing process. A glass substrate manufacturing method that stably suppresses a variation in the heat shrinkage rate generated in the process and stably manufactures a glass substrate having a small heat shrinkage amount is provided.

The present invention provides the following [1] to [6].
[1] A method for measuring a moisture content of a glass substrate by measuring a β-OH value,
A film layer made of a component having a refractive index comparable to that of the glass substrate and not containing a substance having a hydroxyl group is formed on at least one main surface of the glass substrate for measuring the moisture content, and the film A method for measuring a moisture content of a glass substrate, comprising: measuring the moisture content of the glass substrate on which the layer is formed using IR (infrared spectroscopy).
[2] A melting step of melting glass raw material and cullet to form a molten glass, a molding step of a glass substrate for molding the molten glass into a plate shape, and measuring the β-OH value of the glass substrate after the molding A method for producing a glass substrate, comprising a moisture content measuring step for specifying a moisture content of the glass substrate,
In the moisture content measurement step, a coating layer made of a component having a refractive index comparable to that of the glass substrate and not containing a substance having a hydroxyl group is formed on at least one main surface of the glass substrate. A method for producing a glass substrate, comprising: measuring the moisture content of the glass substrate on which the coating layer is formed using IR (infrared spectroscopy).
[3] The β-OH value obtained in the moisture content measurement step is fed back to the melting step,
In the melting step, the mixing ratio of the cullet to the mixture of the glass raw material and cullet is controlled based on a comparison between a predetermined reference β-OH value and the β-OH value actually measured in the moisture content measuring step. The method for producing a glass substrate according to [2].
[4] The β-OH value obtained in the moisture content measurement step is fed back to the melting step,
In the melting step, based on a comparison between a predetermined reference β-OH value and the β-OH value actually measured in the moisture content measuring step, gas heating combustion (oxygen combustion heating) and electricity used for the glass melting are performed. The method for producing a glass substrate according to [2] or [3], wherein the ratio of heating (direct current heating) is controlled.
[5] The method for producing a glass substrate according to any one of [2] to [4], wherein the glass substrate is a glass substrate for a low-temperature polysilicon thin film transistor mounted display.
[6] The method for producing a glass substrate according to any one of [2] to [5], wherein the glass substrate is a glass substrate for a liquid crystal display or a glass substrate for an organic EL display.
[7] The method for producing a glass substrate according to any one of [2] to [6], wherein fluctuation of the β-OH value is suppressed to within ± 0.2.

  According to the glass substrate moisture content measurement method and the glass substrate production method including the moisture content measurement step according to the present invention described above, the β-OH value of the glass substrate after molding is accurately measured in the glass substrate production process. Therefore, while monitoring the moisture content of the glass substrate after molding, the raw material composition, the conditions for melting and heating, the atmospheric conditions outside the platinum device used in the post-processing after melting, etc., more precisely Production conditions can be managed. As a result, the β-OH value of the glass substrate is controlled with high accuracy, and variation in the heat shrinkage rate generated in the manufacturing process can be suppressed, and a glass substrate with a small amount of heat shrinkage can be stably manufactured.

It is a flowchart which shows the flow of the manufacturing method of the glass substrate of this embodiment. It is a figure which shows typically an example of the apparatus which performs the melting process-cutting process in the manufacturing method of the glass substrate of this invention. It is a figure which shows the image of the coating layer on the glass substrate in the moisture content measuring method of this embodiment. (A) is a schematic diagram for explaining a cross-sectional image of a glass substrate on which a film layer is formed, and (b) is a schematic diagram for explaining an image of a cross-sectional surface of a glass substrate in conventional moisture content measurement without forming a film layer. . It is a figure which shows IR transmission spectrum of the Example of this embodiment, and the comparative example (conventional moisture content measurement which does not form a membrane | film | coat layer), (a) And (b) is IR of two typical examples of glass. "Without film layer" is the transmission spectrum measured with the conventional measurement method, and "With film layer" is the transmission spectrum when the film layer is formed on the same sample and measured. is there.

(1) Overview of Manufacturing Method of Glass Substrate The manufacturing method of the glass substrate includes a melting step (ST1), a clarification step (ST2), a homogenization step (ST3), a supply step (ST4), and a molding step ( ST5), a slow cooling step (ST6), and a cutting step (ST7) are mainly included (see FIG. 1). In addition to this, a plurality of glass substrates having a cutting and grinding process, a cleaning process, an inspection process, a packing process, and the like and stacked in the packing process are transported to a supplier.

  The melting step (ST1) is performed in a melting tank. In the melting step, molten glass is made by introducing a glass raw material to the liquid surface of the molten glass stored in the melting tank. Furthermore, molten glass is poured from the outlet provided at the bottom of the melting tank toward the subsequent process.

The melting step (ST1) is performed in a melting furnace. In a melting furnace, a glass raw material is put into a liquid surface of molten glass stored in a melting furnace and heated to make molten glass. Furthermore, molten glass is flowed toward the downstream process from the outlet provided in one bottom part of the inner side wall of the melting furnace.
In addition to the method in which electricity flows through the molten glass itself and heats itself by heating, the glass raw material can be melted by supplementing a flame with a burner. A clarifier is added to the glass raw material. As a fining agent, a metal oxide of a type that releases oxygen by a reduction reaction at a high temperature, such as SnO ₂ , As ₂ O ₃ , Sb ₂ O ₃ , and Fe ₂ O ₃ , is known, but is not particularly limited. However, the use of As ₂ O ₃ as a clarifying agent is not desirable from the viewpoint of reducing environmental burden.

The clarification step (ST2) is performed at least in the clarification tank. In the clarification step, first, the molten glass in the clarification tank is heated to cause a reductive reaction in the clarifier contained in the molten glass to generate O ₂ . This O ₂ is absorbed by bubbles containing CO ₂ , SO _2, N _2, etc. contained in the molten glass due to decomposition reaction of the glass raw material, impurities in the glass raw material, entrainment of the atmosphere during melting, etc. As a result, the bubble diameter of the bubbles in the molten glass is enlarged, and the rising speed of the bubbles is increased. By improving the rising speed of the bubbles, the bubbles are lifted to the liquid surface of the molten glass to promote defoaming. That is, the bubbles that have risen to the liquid surface of the molten glass are broken at the liquid surface, and the gas contained in the bubbles is released into the gas phase space in the clarification tank.
Thereafter, the temperature of the molten glass is lowered to cause the fining agent to oxidize and reabsorb O ₂ in the molten glass. The resorption of the O _2, the small bubbles in the molten glass that has not been degassed, together have a reduced O ₂ is degassing the glass temperature of Awanai, gas pressure in the small bubbles is reduced, the reduction Disappear. In addition, a clarification pipe | tube is provided with the vent pipe connected to air | atmosphere in order to discharge | release the gas discharge | released from the molten glass to the gaseous-phase space to air | atmosphere.

In the homogenization step (ST3), the glass component is homogenized by stirring the molten glass in the stirring tank supplied through the pipe extending from the clarification pipe using a stirrer. Thereby, the composition unevenness of the glass which is a cause of striae or the like can be reduced.
In the supply step (ST4), the molten glass is supplied to the molding apparatus through a pipe extending from the stirring tank.

In the molding apparatus, a molding step (ST5) and a slow cooling step (ST6) are performed.
In the forming step (ST5), the molten glass is formed into a sheet glass to make a flow of the sheet glass. For forming, an overflow downdraw method is used.
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 cutting step (ST7), the sheet glass supplied from the forming device is cut into a predetermined length in the cutting device 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. After this, the end surface of the glass substrate is ground and polished, the glass substrate is cleaned, and after checking for abnormal defects such as bubbles, the glass substrate that has passed the inspection is packed as the final product. The

  Drawing 2 is a figure showing typically an example of the manufacture device of the glass substrate which performs the melting process (ST1)-cutting process (ST7) in this embodiment. As shown in FIG. 2, the apparatus mainly includes a melting apparatus 100, a forming apparatus 200, and a cutting apparatus 300. The melting apparatus 100 includes a melting furnace 101, a clarification tube 102, a stirring tank 103, and glass supply tubes 104, 105, and 106.

In the melting apparatus 101 shown in FIG. 2, the glass raw material is charged using the bucket 101d, but the raw material charging method is not limited, and a screw feeder type or bush plate type charging machine may be used.
In the clarification tube 102, the temperature of the molten glass MG is adjusted, and the clarification of the molten glass MG is performed using the oxidation-reduction reaction of the clarifier. Further, in the stirring vessel 103, the molten glass MG is stirred and homogenized by the stirrer 103a. In the forming apparatus 200, the sheet glass SG is formed from the molten glass MG by the overflow down draw method using the formed body 210.
A flow path of the molten glass MG from the melting furnace 101 to the molding apparatus 200 shown in FIG. 2, specifically, a glass supply pipe 104, a clarification pipe 102, a glass supply pipe 105, a stirring tank 103, and a glass supply pipe 106. At least a part of the inner surface of the flow path forming the flow path of the molten glass MG is made of platinum or a platinum alloy.

(2) Glass substrate The glass substrate manufactured in the embodiment of the present invention is, for example, a glass substrate for flat panel display or a glass substrate for curved panel display, for example, a glass substrate for liquid crystal display or an organic EL display. It is suitable as a glass substrate. In addition, the glass substrate can also be used as a display for a portable terminal device, a cover glass for a housing, a touch panel plate, a glass substrate for a solar cell, or a cover glass. Particularly, it is suitable for a glass substrate for liquid crystal display. Panel manufacturing such as LTPS (low temperature polysilicon) TFT, oxide semiconductor TFT, IGZO (Indium-Gallium-Zinc-Oxide) TFT display glass substrate, etc., which are required to have particularly low thermal shrinkage. It can be suitably used for products that require high temperature treatment in the process.

Although the glass substrate manufactured in this embodiment is not particularly limited, for example, the vertical dimension and the horizontal dimension are 500 mm to 3500 mm, 1500 mm to 3500 mm, 1800 to 3500 mm, 2000 mm to 3500 mm, etc., and 2000 mm to 3500 mm. Preferably there is.
The thickness of the glass substrate is, for example, 0.01 mm to 1.1 mm. More preferably, it is a very thin rectangular plate of 0.75 mm or less, and for example, a thickness of 0.55 mm or less, more preferably 0.45 mm or less is more preferable. As a lower limit of the thickness of a glass substrate, 0.15 mm or more is preferable and 0.25 mm or more is more preferable.

As a glass substrate manufactured by this embodiment, the glass substrate of the following glass compositions is illustrated. That is, the raw material of molten glass is prepared so that the glass substrate of the following glass compositions is manufactured.
<Glass composition>
Examples of the glass composition to which the present embodiment is applied include the following (mass% display).
SiO _2: 50~70% _{(preferably, 57~64%), Al 2 O} 3: 5~25% ( _{preferably, 12~18%), B 2 O} 3: 0~15% ( preferably, 6 ~ 13%), and may optionally contain the following composition. As optional components, MgO: 0 to 10% (preferably 0.5 to 4%), CaO: 0 to 20% (preferably 3 to 7%), SrO: 0 to 20% (preferably, from 0.5 to 8%, more preferably 3~7%), BaO: 0~10% ( preferably 0-3%, more preferably _{0~1%), ZrO 2: 0~10} % ( preferably 0-4%, more preferably _{0~1%), P 2 O 5} : 0~5% ( preferably 0-3%) can be mentioned. Furthermore, it is more preferable that R ′ ₂ O: more than 0.10% and 2.0% or less (provided that R ′ is at least one selected from Li, Na, and K).
_{Alternatively,} SiO 2: _{50~70% (preferably, 55~65%), B 2 O} 3: 0~10% ( _{preferably, 0~5%, 1.3~5%),} Al 2 O 3: 10-25% (preferably 16-22%), MgO: 0-10% (preferably 0.5-4%), CaO: 0-20% (preferably 2-10%, 2-6 %), SrO: 0 to 20% (preferably 0 to 4%, 0.4 to 3%), BaO: 0 to 15% (preferably 4 to 11%), RO: 5 to 20% (preferably Is preferably 8 to 20%, 14 to 19%), P ₂ O ₅ : 0 to 5% (preferably 0 to 3%), where R is Mg, Ca, Sr and Ba At least one kind selected from: Furthermore, it is more preferable that R ′ ₂ O contains more than 0.10% and 2.0% or less (provided that R ′ is at least one selected from Li, Na and K).
Furthermore, the following are mentioned as a physical-property value of the glass substrate of this embodiment.
<Young's modulus>
As a Young's modulus of the glass substrate to which this embodiment is applied, for example, 72 (Gpa) or more is preferable, 75 (Gpa) or more is more preferable, and 77 (Gpa) or more is even more preferable.
<Strain point>
As a distortion rate of the glass substrate to which this embodiment is applied, 650 degreeC or more is preferable, for example, 680 degreeC or more is more preferable, 700 degreeC or more and 720 degreeC or more are still more preferable.
Further, for example, the liquid phase viscosity of the glass substrate is 10 ^4.3 poise to 10 ^6.7 poise.
Of course, in the present invention, the glass composition of the glass substrate is not limited.
<Others>
As a method for forming sheet glass from molten glass in this embodiment, a float method, a fusion method, or the like is used. However, a method for manufacturing a glass substrate including offline heat treatment of the glass substrate in this embodiment is a fusion method (overdown). The draw method is suitable for the fusion method because it is difficult to lengthen the slow cooling device on the production line. The thermal shrinkage rate of the glass substrate before reducing the thermal shrinkage rate by the heat treatment of this embodiment is maintained at a temperature of 500 ° C. for 30 minutes and then allowed to cool to room temperature. And 50 ppm or less, preferably 40 ppm or less, more preferably 30 ppm or less, and even more preferably 20 ppm or less.
Accompanying the demand for a glass substrate having a small heat shrinkage rate, it is required to measure a minute amount of heat shrinkage with high accuracy. As a method for measuring the thermal shrinkage rate, the thermal shrinkage rate (C) of the glass substrate is [C (thermal shrinkage rate) = (L ₀ −L) / L ₀ (where L _{0 is} a glass plate before thermal shrinkage). , L: length of glass plate after heat shrinkage), for example, heat shrinkage rate (ppm) = {shrinkage amount of glass in heat treatment / distance between marking lines of glass before heat treatment} × 10 ⁶ Desired.

  As a method for forming sheet glass from molten glass in this embodiment, a float method, a fusion method, or the like is used. However, a method for manufacturing a glass substrate including offline heat treatment of the glass substrate in this embodiment is a fusion method (overdown). The draw method is suitable for the fusion method because it is difficult to lengthen the slow cooling device on the production line.

(3) Measuring method of moisture content of glass substrate (3-1) Features The measuring method of moisture content of the glass substrate of the present invention is a measuring method of moisture content of the glass substrate by measuring β-OH value,
A film layer (see FIG. 3 (a)) having a refractive index comparable to that of the glass substrate and not containing a substance having a hydroxyl group is used as the main object of the glass substrate for the water content measurement. The moisture content of the glass substrate formed on the surface and having the coating layer formed thereon is measured using IR (infrared spectroscopy).

(3-2) Forming method of coating layer The component (substance) that forms the coating layer on the main surface of the glass plate whose moisture content is to be measured is the same as the glass to be measured (the glass containing an inorganic material as a component). The component (substance) having a refractive index is appropriately selected from materials having no hydroxyl group (—OH), and the type and the component are not particularly limited.
For example, when the refractive index of the glass plate for measuring the moisture content is “1.5”, it is a component (substance) having a refractive index in the range of 1.3 to 1.7 and does not have a hydroxyl group (—OH). Selected from substances. That is, the difference between the refractive index of the glass plate for measuring the moisture content and the refractive index of the coating layer should be within ± 0.2, preferably within ± 0.1, more preferably within ± 0.05. .
Examples of the material of the coating layer formed on the main surface of the glass plate include oil, a gel material, and a resin.
The film layer on the glass plate may be a liquid film layer, a solid film layer, or a highly viscous film layer that is not completely solid.

As a method of forming a coating layer on the main surface of the glass plate for measuring the moisture content, for example, a liquid coating layer component is applied on the main surface of the glass plate, and a liquid coating layer having a predetermined thickness is formed. In the state formed on the main surface of the glass plate, the infrared absorption spectrum of the glass plate having the coating layer can be measured.
The coating method for applying the liquid coating layer substance is not particularly limited as long as the coating layer can be formed with a predetermined thickness on the main surface of the glass plate. Use it.

  Even when a solid film layer is formed on the main surface of the glass plate for measuring the moisture content, the method for forming the film layer is not particularly limited. For example, first, a liquid film layer component is formed on the main surface of the glass plate. If a coating layer with a predetermined thickness is formed on the main surface of the glass plate and the main surface of the coating layer that is not in contact with the glass plate is smooth and has no irregularities, and has a very high smoothness, it is solid. A coating layer may be formed. The same applies when a highly viscous coating layer that is not completely solid is formed on a glass plate.

  The thickness for forming the coating layer on the main surface of the glass plate may be, for example, in the range of 1/10 to 1/1000 of the thickness of the glass plate, or the main surface of the coating layer not in contact with the glass plate As long as the film can be kept smooth and free of irregularities, the thickness of the coating layer may be thicker or thinner than this range.

[Measurement of β-OH value]
The β-OH value [mm ⁻¹ ] of glass is determined by the following formula in the spectrum obtained by measuring an infrared absorption spectrum with IR of glass.
β-OH value = (1 / X) log ₁₀ (T1 / T2)
X: Glass thickness (mm)
T1: Transmittance (%) at a reference wavelength of 2600 nm
T2: Minimum transmittance (%) near the hydroxyl absorption wavelength of 2800 nm
Usually, as a moisture content calculation of a glass plate, a plurality of samples are cut out from a glass substrate obtained under the same conditions, and a β-OH value is measured for the plurality of samples to obtain a moisture content.

  As described above, a coating layer made of a component having a refractive index comparable to that of the glass substrate and not containing a substance having a hydroxyl group is formed on the main surface of the glass substrate, and the coating layer is formed on the main surface. When the moisture content of a glass substrate is measured by IR, the infrared absorption spectrum becomes smooth and a stable infrared absorption spectrum is obtained, so that a more accurate β-OH value can be measured, and the accuracy of moisture content measurement. Will improve.

(4) Moisture content measurement step and feedback process of glass substrate (4-1) Feedback control in glass raw material and cullet raw material composition One of the glass substrate manufacturing methods of the present embodiment is the moisture content measurement method of the present invention. On the basis of the moisture content of the glass substrate after forming and cooling, after measuring the β-OH value using the absorbance (β-OH value) due to the OH group in the glass substrate by infrared spectroscopy (measured β- OH value), in the melting step, based on a comparison between a predetermined reference β-OH value and an actually measured β-OH value, a mixing ratio of cullet (hereinafter also referred to as cullet ratio) with respect to a mixture of the glass raw material and cullet. Includes feedback process of controlling raw material formulation. The installation of the moisture content measurement step of the present invention may include, for example, feeding back the glass substrate after the slow annealing in preparation for the slow cooling of the molding or before the melting step.

The reason why the cullet is used together with the glass raw material is to reduce the energy for melting the glass raw material. Since the cullet is melted once and vitrified, it can be melted with less energy compared to melting the glass raw material. In addition, by using cullet together with the glass raw material, it is possible to suppress the generation of industrial waste and to reduce the raw material cost by reusing the glass that does not become a product generated in the manufacturing process of the glass substrate.
The glass raw materials, which are the components such as _{SiO 2, Al 2 O 3,} B 2 O 3 that is provided so as to be the composition of the glass substrate to be described later. The cullet is glass or glass waste called an ear generated in the glass substrate manufacturing process. The ears are portions on both sides in the width direction of the sheet glass, which were cut from the glass plate in the cutting step (ST8).

The moisture in the glass substrate must remain in the glass without being released from the molten glass or from the atmosphere near the liquid surface of the molten glass in the melting tank. Is contained in the glass substrate. In order to keep the moisture content in the glass substrate constant, it is mentioned to keep the moisture content in the glass raw material, the glass melting temperature in the melting tank, and the molten glass amount constant.
However, in order to realize the thickness of the glass substrate to be manufactured and the required quality, it is necessary to change the glass melting temperature in the melting tank or to change the amount of molten glass in the melting tank. As a result, the amount of moisture in the glass substrate changes, and it is difficult to keep the amount of moisture in the glass substrate constant. In addition, the amount of water in the glass substrate may change unintentionally due to external factors.

Therefore, in the method for producing a glass substrate of the present embodiment, the measured data (actually measured β-OH value) of the moisture content of the glass substrate after the slow cooling of molding is monitored using the β-OH value measuring method of the present invention. Furthermore, by feeding back to the melting process and controlling the blending ratio of the cullet to the mixture of the glass raw material and the cullet based on the comparison between the predetermined reference β-OH value and the measured β-OH value, in the glass substrate It is possible to more accurately and accurately suppress the influence of fluctuations in the amount of water.
In the melting step (ST2), the amount of cullet with respect to the glass raw material is controlled, and in the melting step (ST2), the glass raw material and cullet are optimally mixed and adjusted according to the cullet ratio.

  As described above, the moisture content (β-OH value) is monitored according to the method for measuring the moisture content of the glass substrate of the present invention, and the measured β-OH value of the glass substrate is reflected in the manufacturing process of the next glass substrate. By performing feedback control in the blending, the β-OH value of the glass substrate can be managed with high accuracy.

(4-2) Feedback process of combustion heating control in melting tank One of the methods for producing a glass substrate of the present embodiment is based on the moisture content measuring method of the present invention. After measuring the β-OH value using the absorbance (β-OH value) due to the OH group in the glass substrate by infrared spectroscopy (measured β-OH value), in the melting step, a predetermined reference β- Based on the comparison between the OH value and the measured β-OH value, the ratio of the gas heating combustion (oxygen combustion heating) and the electric heating (direct current heating) used for the glass melting is controlled. Includes processes. The installation of the moisture content measurement step of the present invention may include, for example, feeding back the glass substrate after the slow annealing in preparation for the slow cooling of the molding or before the melting step.

  The melting step (ST2) is performed in a melting tank. In the melting tank, molten glass is made by introducing the glass raw material and cullet into the liquid surface of the molten glass stored in the melting tank in accordance with the cullet ratio. Glass raw material and cullet charging method, for example, a method of inverting the bucket containing the glass raw material etc. and putting it into the molten glass in the melting tank, or a method of feeding the glass raw material etc. using a belt conveyor, A method of feeding glass raw material or the like with a screw feeder may be used. In this embodiment, a glass raw material etc. are supplied using a bucket.

The molten glass of the melting tank may be heated by, for example, radiant heat from a flame of a burner, and an electric current is passed between at least one pair of electrodes (not shown) made of molybdenum, platinum, tin oxide, or the like. The glass raw material may be melted by supplementary heating with a burner in addition to the current heating. In this embodiment, heating is performed by radiant heat from the flame of the burner and energization heating.
A fining agent is added to the glass raw material and cullet to be charged. SnO ₂ , As ₂ O ₃ , Sb ₂ O _{3 and the} like are known as fining agents, but are not particularly limited. However, it is preferable to use SnO2 (tin oxide) as a clarifying agent from the viewpoint of reducing environmental burden.

If the ratio of combustion heating typified by a burner is too high, the β-OH value of the glass substrate to be produced becomes high and the strain point becomes small, so that the variation in the heat shrinkage rate also becomes large.
As one of the embodiments, the actual measurement data (actual β-OH value) of the moisture content of the glass substrate after forming and cooling is monitored using the β-OH value measurement method of the present invention, and further to the melting step. It is possible to control the ratio of combustion heating and electric heating based on a comparison between a predetermined reference β-OH value and a measured β-OH value.

For example, in a melting tank, SnO ₂ is produced by using combustion heating in a gas phase using combustion means such as a burner and energization heating performed by passing a current through the molten glass using a pair of electrodes or the like. In the case where the glass raw material is melted so that the temperature is 1580 ° C. or more when the viscosity is 102.5 poises, at this time, using a predetermined reference β-OH value as an index, By measuring the moisture content (measured β-OH value) of the glass substrate, it is possible to check whether combustion heating and current heating are optimally performed. For example, by measuring and monitoring the moisture content (measured β-OH value) of the glass substrate after forming so that the combustion heating ratio does not become too high in the ratio of combustion heating and electric heating heating value, Combustion heating and energization heating can always be controlled optimally so that the ratio of the heating value by combustion heating to the heating value by combustion heating in the process is 1.5 or more and 2.8 or less.

If the ratio of combustion heating typified by a burner is too high, the β-OH value of the glass substrate to be produced becomes high and the strain point becomes small, so that the variation in the heat shrinkage rate also becomes large. Moreover, since the contribution of the heat generated by combustion heating increases and the temperature of the gas phase space increases, oxygen in the fining agent such as SnO ₂ contained in the glass raw material in the state of the glass raw material on the liquid surface of the molten glass. Oxygen diffuses as it is released into the gas phase space. For this reason, when the molten glass is defoamed in the refining process, which is a subsequent process, sufficient oxygen is not supplied from the refining agent contained in the molten glass, and the bubbles contained in the molten glass are allowed to grow by absorbing oxygen. It is not possible to release bubbles by raising the bubbles to the liquid surface of the glass. That is, the defoaming process cannot be performed sufficiently. This problem becomes prominent when SnO ₂ is used as a clarifier without using As ₂ O _3, which has a high clarification effect.

On the other hand, if the ratio of current heating is too high, the contribution of the amount of heat generated by current heating becomes relatively large, and the current that flows for current heating increases. Here, when the glass composition is adjusted so as to increase the strain point, the temperature when the viscosity is 10 ^2.5 poise tends to increase, and the specific resistance of the molten glass also tends to increase. For example, when glass containing SnO ₂ and having a viscosity of 10 ^2.5 poise and having a temperature of 1580 ° C. or higher is the ratio of the refractory bricks on the bottom wall of the melting tank at the temperature of the molten glass stored in the melting tank The difference from the resistance is reduced. This tendency is particularly noticeable in a glass substrate for an active matrix flat panel display that is substantially free of alkali metal oxide or has an alkali metal oxide content of 0% by mass to 0.8% by mass. Become.
For this reason, a part of electric current supplied to a pair of electrodes flows into the bottom wall of a melting tank main body instead of molten glass, and a bottom wall is electrically heated. Therefore, when making molten glass with high specific resistance and high temperature viscosity in the melting tank, a large amount of current is supplied to the electrode pair, so that a large amount of current flows also to the bottom wall. Will grow. Due to the increase in the amount of heat generated at the bottom wall, a phenomenon occurs in which heat is trapped due to the heat insulation characteristics of the bottom of the melting tank. This heat weight may weaken the mechanical strength of the refractory bricks at the bottom to cause thermal creep and deform the bottom. Furthermore, there is a possibility that the temperature of the refractory brick exceeds the heat resistance temperature and is melted by the heat. For this reason, it is not preferable that the contribution of the amount of heat generated by energization heating is excessive.

  In view of the above points, it is preferable that the ratio of the amount of heat generated by combustion heating to the amount of heat generated by energization heating is 1.5 to 2.8.

  The amount of heat generated by energization heating can be obtained by, for example, measuring power consumption from a power meter. The amount of power consumed (kW) is converted into the amount of heat generated by energization heating (kcal / hour) (1 kW = 860 kcal / hour). Note that the power consumption may be obtained from the voltage applied to the electrode 114 and the current flowing through the electrode 114. The calorific value of combustion heating using the combustion gas is calculated by multiplying the calorific value per unit volume due to combustion of the combustion gas by the supply amount of combustion gas per unit time (flow rate of combustion gas). The ratio of the calorific value used in the present embodiment is the ratio of the average value of the calorific value per certain time. Here, the fixed time may be one hour or one day.

A glass raw material prepared to have the following glass composition is melted at 1560 to 1640 ° C. using a continuous melting apparatus equipped with a refractory brick melting tank and a platinum alloy adjustment tank (clarification tank), and 1620 to After clarifying at 1670 ° C. and stirring at 1440-1530 ° C., it was formed into a thin plate with a thickness of 0.7 mm by the overflow down draw method, and the average speed was 100 ° / min within the temperature range of Tg to Tg−100 ° Was slowly cooled to obtain a glass substrate for liquid crystal display (for organic EL display).
The refractive index of the obtained glass substrate was about 1.51. A solution having a refractive index of 1.515 was applied to both surfaces (main surface) of the glass substrate. The solution used was a liquid that did not contain water and was more viscous than water. A film having a refractive index comparable to that of the glass substrate was formed on the main surface of the glass substrate, and the infrared absorption spectrum was measured by IR for the glass substrate having the film on the main surface. The spectrum results are shown in FIG. The β-OH value was calculated based on the following measurement formula.
(Used glass)
_{SiO 2: 60~65%, Al 2} O 3: 15~20%, B 2 O 3: 10~15%, MgO: 0~5%, CaO: 0~10%, SrO: 0~5%, BaO : Set to 0 to 5%. If it still fails, SiO ₂ : 60%, Al ₂ O ₃ : 16%, B ₂ O ₃ : 10%, MgO: 2%, CaO: 8%, SrO: 2%, BaO: 2%
(Glass shape)
The thickness of the glass of Example (a) was 0.7 mm, and the thickness of the glass of Example (b) was 0.5 mm.
[Measurement of β-OH value]
The β-OH value [mm ⁻¹ ] of glass is determined by the following formula in the spectrum obtained by measuring an infrared absorption spectrum with IR of glass.
β-OH value = (1 / X) log ₁₀ (T1 / T2)
X: Glass thickness (mm)
T1: Transmittance (%) at a reference wavelength of 2600 nm
T2: Minimum transmittance (%) near the hydroxyl absorption wavelength of 2800 nm
The value of β-OH of Example (a) calculated by this method is in the range of 0.320 to 0.330 in the case of no coating layer (conventional moisture measurement without forming a coating layer), While there was a variation of 0.010, when the coating layer was present, the variation was in the range of 0.320 to 0.325 and 0.005.
Moreover, the value of β-OH in Example (b) is in the range of 0.229 to 0.279 in the case of no coating layer, and there was a variation of 0.050, whereas there was a coating layer. In the case, the variation was 0.021 within the range of 0.224 to 0.245.
In the case of Example (a), the variation in the measured value of β-OH could be reduced by forming the coating layer in both cases of Example (b).

  Moisture of a glass substrate having a refractive index comparable to that of the glass substrate and having a coating layer made of a component not containing a substance having a hydroxyl group on the main surface of the glass substrate and having the coating layer on the main surface When the amount was measured by IR, the infrared absorption spectrum was constant, and a stable infrared absorption spectrum was obtained. Therefore, a more accurate β-OH value could be measured, and the accuracy of water content measurement was improved. According to the moisture content measuring method of the present invention, the fluctuation of the β-OH value obtained by the measurement can be suppressed to within ± 0.2.

  As described above, according to the moisture content measuring method by the β-OH measuring method of the glass substrate of the present invention, the β-OH value can be easily measured with high accuracy, and the β of the glass substrate can be measured during the manufacturing process. Since the information of -OH value can be monitored with high accuracy, in the glass substrate manufacturing method, by including the measuring step of the moisture content measuring method of the present invention, the composition of raw materials, the conditions for melting and heating, the molten glass It is possible to accurately manage the atmospheric conditions and the like outside the platinum device used in the processing step. Thereby, while suppressing the variation in the thermal contraction rate which generate | occur | produces in a manufacture process, the glass substrate with small heat shrinkage amount can be manufactured stably.

  As mentioned above, although the manufacturing apparatus of the glass substrate of this invention and the manufacturing method of the glass substrate were 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, various improvement and change You may do.

DESCRIPTION OF SYMBOLS 100 Glass substrate manufacturing apparatus 101 Melting tank 102 Clarification tube 103 Stirrer tank (stirrer)
104 Glass supply pipe 1
105 Glass supply tube 2
106 Glass supply tube 3
DESCRIPTION OF SYMBOLS 110 Dissolution tank wall surface 112 Electrode 200 Molding device 210 Molded body 300 Cutting device 400 Film layer 401 having refractive index equivalent to glass substrate Glass substrate

Claims (6)

A method for measuring a moisture content of a glass substrate by measuring a β-OH value,
A film layer made of a component having a refractive index comparable to that of the glass substrate and not containing a substance having a hydroxyl group is formed on at least one main surface of the glass substrate for measuring the moisture content, and the film A method for measuring a moisture content of a glass substrate, comprising measuring the moisture content of the glass substrate on which the layer is formed using IR (infrared spectroscopy). The glass substrate by melting a glass raw material and cullet to form a molten glass, a glass substrate forming step for forming the molten glass into a plate shape, and measuring the β-OH value of the glass substrate after the forming A method for producing a glass substrate, comprising a moisture content measurement step for specifying the moisture content of
In the moisture content measurement step, a coating layer made of a component having a refractive index comparable to that of the glass substrate and not containing a substance having a hydroxyl group is formed on at least one main surface of the glass substrate. A method for producing a glass substrate, comprising: measuring the moisture content of the glass substrate on which the coating layer is formed using IR (infrared spectroscopy). Feeding back the actual β-OH value measured in the moisture content measurement step to the melting step,
In the melting step, based on a comparison between a predetermined reference β-OH value and an actually measured β-OH value measured in the moisture content measurement step, the blending ratio of the cullet to the mixture of the glass raw material and cullet is determined. The manufacturing method of the glass substrate of Claim 2 controlled. Feeding back the actual β-OH value measured in the moisture content measurement step to the melting step,
In the melting step, based on a comparison between a predetermined reference β-OH value and an actual β-OH value measured in the moisture content measuring step, gas heating combustion (oxygen combustion heating) used for the glass melting, The manufacturing method of the glass substrate of Claim 2 or 3 which controls the ratio of an electrical heating (direct current heating).   The said glass substrate is a manufacturing method of the glass substrate as described in any one of Claims 2-4 which is a glass substrate for low-temperature polysilicon thin-film transistor mounted displays.   The said glass substrate is a manufacturing method of the glass substrate as described in any one of Claims 2-5 which is a glass substrate for liquid crystal displays, or a glass substrate for organic EL displays.

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