JP5797222B2 - Glass substrate manufacturing method and manufacturing apparatus - Google Patents

Description

  The present invention relates to a glass substrate manufacturing method and a manufacturing apparatus.

  In recent years, flat panel displays such as liquid crystal displays and organic EL displays have been required to display high-definition images, and glass substrates used for displays are not α-Si TFT (Amorphous Silicon Thin Film Transistor), It is required to be applicable to low-temperature polysilicon (hereinafter referred to as LTPS) TFT. When manufacturing a panel of LTPS • TFT, heat treatment at a higher temperature is required as compared with α-Si • TFT. However, when such a high-temperature heat treatment is performed on the glass substrate on which the TFT is formed, the glass substrate shrinks due to thermal shrinkage, and a shift of the TFT circuit formed on the glass substrate occurs. Such a shift causes a display defect in a display such as a liquid crystal panel. For this reason, the glass substrate on which LTPS · TFT is formed is required to have a small thermal shrinkage rate and a small variation in the thermal shrinkage rate for each glass substrate.

  Generally, the thermal shrinkage rate of a glass substrate decreases as the viscosity of the glass in a low temperature range increases, that is, as the strain point of the glass increases. Thus, conventionally, a technique has been proposed in which the strain point is increased by adjusting the composition of the glass raw material, thereby reducing the thermal shrinkage rate of the glass substrate (Patent Document 1).

JP 2011-126728 A

By the way, when manufacturing a glass substrate, even if the cooling conditions at the time of slow cooling are constant, the thermal contraction rate may vary for each glass substrate obtained depending on the time of production. The reason for the variation in thermal shrinkage is that the amount of moisture contained in the molten glass varies depending on the production period, resulting in different amounts of moisture for each glass substrate, resulting in different strain points and different thermal shrinkage rates. Can be mentioned. Such a variation in the thermal shrinkage rate is not preferable as a glass substrate applied to the LTPS • TFT.
This is because the problem of TFT circuit misalignment due to the large absolute value of the thermal contraction rate can be reduced by changing the device settings during the manufacture of the LTPS / TFT panel. On the other hand, the influence of the variation in the thermal shrinkage rate for each glass substrate is particularly important because it is difficult to reduce even if the apparatus setting is changed.
However, with the technique disclosed in Patent Document 1, even if the absolute value of heat shrinkage can be reduced, variation in the heat shrinkage rate of each glass substrate cannot be sufficiently suppressed.

  An object of this invention is to provide the manufacturing method and manufacturing apparatus of a glass substrate which can suppress the variation in the thermal contraction rate for every glass substrate.

One aspect of the present invention is a melting step in which a glass raw material and cullet are melted to produce a molten glass,
A method for producing a glass substrate for display, comprising producing a glass substrate having a strain point of 680 degrees or more, comprising a molding step of forming the molten glass into a sheet glass,
In order to reduce the variation of the strain point and the heat shrinkage rate for each glass substrate by setting the variation of β-OH value for each glass substrate to ± 0.015 / mm or less, β A control step of adjusting the β-OH value of the glass substrate by controlling the blending ratio of the cullet with respect to the mixture with the cullet having a high -OH value;
In the control step,
By determining the β-OH value of the manufactured glass substrate to determine the amount of change in β-OH value due to changes in manufacturing conditions,
Wherein the beta-OH value of the glass substrate, the so that the thermal shrinkage of the glass substrate becomes a predetermined target beta-OH value to be equal to or less than 70 ppm, based on the change amount of the beta-OH value Control the mixing ratio of cullet ,
The heat shrinkage rate is 10 ° C./min from room temperature, held at 550 ° C. for 1 hour, then lowered to room temperature at 10 ° C./min, raised again at 10 ° C./min, and heated at 550 ° C. Using the amount of shrinkage of the glass substrate after the heat treatment for holding for 1 hour and lowering to room temperature at 10 ° C./min, the following formula:
Thermal shrinkage rate (ppm) = {Shrinkage amount of glass substrate by heat treatment / Length of glass substrate before heat treatment} × 10 ⁶
Ru der ones determined by, characterized in that.
According to this manufacturing method, the β-OH value of the glass substrate is controlled by controlling the compounding ratio of the cullet to the mixture of the glass raw material and the cullet so that the β-OH value of the glass substrate becomes the target β-OH value. Even if the manufacturing conditions that give the change are changed, it is possible to suppress the change in the β-OH value of the manufactured glass substrate, and to reduce the variation in the β-OH value for each glass substrate. Therefore, the variation of the strain point for each glass substrate can be reduced, and the variation of the thermal shrinkage rate for each glass substrate can be reduced.

In the first preferred embodiment of the method for producing a glass substrate, in the melting step, the glass raw material and cullet are charged into a melting tank according to a blending ratio determined based on a β-OH value of the produced glass substrate. .
In addition, it is more preferable that the said mixture ratio is determined based on the change result or schedule of the manufacturing conditions which influence (beta) -OH value amount in glass.
As described above, the β-OH value of the glass substrate is reflected when the glass substrate is manufactured next, and the feedback control is performed, so that the β-OH value of the glass substrate can be accurately controlled.

  In a second preferred embodiment of the method for producing a glass substrate, the glass substrate has a strain point of 680 degrees or more.

In a third preferred embodiment of the method for producing a glass substrate, the glass substrate has a total content of Li ₂ O, Na ₂ O, and K ₂ O of 0 to 2% by mass.

In a fourth preferred embodiment of the method for producing a glass substrate, the glass substrate is a flat panel display glass substrate.
In a fifth preferred embodiment of the method for producing a glass substrate, the glass substrate is a glass substrate for a LTPS / TFT mounted display.
Moreover, in the 6th preferable form of the manufacturing method of the said glass substrate, the said glass substrate is a glass substrate for liquid crystal displays or a glass substrate for organic EL displays.

In a preferred seventh embodiment of the method for producing a glass substrate, in the melting step of melting a glass raw material and cullet in a melting tank to form a molten glass, combustion heating in a gas phase using a combustion means, and melting glass The glass raw material is melted so that the glass containing SnO _{2 and} having a viscosity of 10 ^2.5 poise and having a temperature of 1580 ° C. or higher is obtained by using the electric heating performed by passing an electric current. The combustion heating and the energization heating are performed so that the ratio of the heat generation amount due to the combustion heating to the heat generation amount due to the combustion heat is from 1.5 to 2.8.
As a result, the β-OH value of the glass substrate is increased, and it is possible to suppress the strain point from being reduced, and the variation in heat collection / shrinkage can be reduced. Furthermore, the clarification of the molten glass can be performed efficiently, and damage or melting of the melting tank can be suppressed.

Another aspect of the present invention is a melting tank for melting glass raw material and cullet to make molten glass,
A glass substrate manufacturing apparatus for manufacturing a glass substrate for display having a strain point of 680 degrees or more, and a molding furnace for forming the molten glass into a sheet glass,
In order to reduce the variation of the strain point and the heat shrinkage rate for each glass substrate by setting the variation of β-OH value for each glass substrate to ± 0.015 / mm or less, β A control unit for adjusting the β-OH value of the glass substrate by controlling the blending ratio of the cullet with respect to the mixture with the cullet having a high -OH value;
In the control unit,
By determining the β-OH value of the manufactured glass substrate to determine the amount of change in β-OH value due to changes in manufacturing conditions,
Wherein the beta-OH value of the glass substrate, the so that the thermal shrinkage of the glass substrate becomes a predetermined target beta-OH value to be equal to or less than 70 ppm, based on the change amount of the beta-OH value Control the mixing ratio of cullet ,
The heat shrinkage rate is 10 ° C./min from room temperature, held at 550 ° C. for 1 hour, then lowered to room temperature at 10 ° C./min, raised again at 10 ° C./min, and heated at 550 ° C. Using the amount of shrinkage of the glass substrate after the heat treatment for holding for 1 hour and lowering to room temperature at 10 ° C./min, the following formula:
Thermal shrinkage rate (ppm) = {Shrinkage amount of glass substrate by heat treatment / Length of glass substrate before heat treatment} × 10 ⁶
Ru der ones determined by, characterized in that.
According to this manufacturing apparatus, the blending ratio of cullet to the mixture of the glass raw material and the cullet is controlled so that the β-OH value of the glass substrate becomes the target β-OH value, whereby the β-OH value of the glass is obtained. Even if the production conditions that affect it change, it is possible to suppress the change in the β-OH value of the manufactured glass substrate, and to reduce the variation in the β-OH value for each glass substrate to be obtained. Therefore, the variation of the strain point for each glass substrate can be reduced, and the variation of the thermal shrinkage rate for each glass substrate can be reduced.

Another aspect of the present invention is a method of manufacturing a glass substrate,
A melting step for producing molten glass, a molding step for molding the molten glass into a sheet glass,
And the β-OH value of the glass substrate is controlled to be a target β-OH value.
According to this manufacturing method, even if the manufacturing condition affecting the β-OH value of the glass is changed by controlling the β-OH value of the glass substrate to be the target β-OH value, the glass substrate is manufactured. It is possible to suppress a change in the β-OH value of the glass substrate, and to reduce the variation in the thermal shrinkage rate for each glass substrate.

According to the present invention, β-OH for each glass substrate obtained by controlling the compounding ratio of cullet to the mixture of glass raw material and cullet so that the β-OH value of the glass substrate becomes the target β-OH value. The variation in value is reduced. Therefore, the variation of the strain point for each glass substrate is reduced, and the variation of the thermal shrinkage rate for each glass substrate is reduced. Moreover, according to this manufacturing method, the β-OH value of the glass substrate can be easily adjusted by controlling the blending ratio of cullet.
Further, by controlling the β-OH value of the glass substrate to be the target β-OH value, variation in β-OH value for each glass substrate to be obtained is reduced. Therefore, the variation of the strain point for each glass substrate is reduced, and the variation of the thermal shrinkage rate for each glass substrate is reduced.

It is a figure which shows an example of the process of the manufacturing method of the glass substrate of this invention. It is a figure which shows typically an example of the apparatus which performs the determination process-measurement process shown in FIG. It is a figure explaining the melting tank of the manufacturing apparatus of the glass substrate of this invention.

  The glass substrate manufacturing method and glass substrate manufacturing apparatus of the present invention will be described below.

(Glass substrate manufacturing method)
First, the manufacturing method of a glass substrate is demonstrated.
In FIG. 1, the figure explaining an example of the flow of the manufacturing method of a glass substrate is shown.
The manufacturing method of the glass substrate includes a determination process (ST1), a melting process (ST2), a clarification process (ST3), a homogenization process (ST4), a supply process (ST5), a molding process (ST6), It has mainly a slow cooling process (ST7), a cutting process (ST8), and a measurement process (ST9). The control process of the manufacturing method of the glass substrate of the present invention includes a determination process (ST1) and a measurement process (ST9). In addition to this, the glass substrate of the final product is obtained through a grinding process, a polishing process, a cleaning process, an inspection process, a packing process, and the like.

In the control step, the absorbance (β-OH value) due to the OH group in the glass substrate by infrared spectroscopy is used as the moisture content of the glass substrate, and the β-OH value in the glass substrate becomes the target β-OH value. The blending ratio of cullet to the mixture of glass raw material and cullet (hereinafter also referred to as cullet ratio) is controlled. 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 glass substrate manufacturing method of the present embodiment, the influence of fluctuations in the amount of moisture in the glass substrate is suppressed by controlling the blending ratio of cullet to the mixture of the glass raw material and cullet. Such control of the cullet ratio is performed prior to the melting step (ST2), so that in the melting step (ST2), the glass raw material and the cullet are charged according to the controlled cullet ratio. The control process will be described later in detail.

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 determined in the control step. 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 SnO ₂ (tin oxide) as a clarifying agent from the viewpoint of reducing environmental burden.

In the present embodiment, in the melting tank, combustion heating in the gas phase using a 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 are used. Thus, the glass raw material can be melted so that the glass contains SnO ₂ and the temperature when the viscosity is 10 ^2.5 poise is 1580 ° C. or higher. At this time, it is preferable that the combustion heating and the current heating are performed so that the ratio of the heat generated by the combustion heating to the heat generated by the current heating 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 heat collection and shrinkage 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.

The clarification step (ST3) is performed at least in the clarification tank. In the clarification step (ST3), the molten glass in the clarification tank is heated, so that bubbles containing O ₂ , CO _2, or SO ₂ contained in the molten glass are produced by the reduction reaction of the clarifier. _It absorbs ₂ and grows, and bubbles rise to the liquid surface of the molten glass and are released. Furthermore, in the clarification step, the reducing substance obtained by the reduction reaction of the clarifier undergoes an oxidation reaction by lowering the temperature of the molten glass. Thereby, gas components such as O ₂ in the foam remaining in the molten glass are reabsorbed in the molten glass, and the foam disappears. The oxidation reaction and reduction reaction by the fining agent are performed by controlling the temperature of the molten glass. In the clarification step, a reduced pressure defoaming method in which a reduced pressure atmosphere is created in a clarification tank and bubbles present in the molten glass are grown in a reduced pressure atmosphere and defoamed can be used. in this case,
It is effective in that no clarifier is used. In the clarification step described later, a clarification method using tin oxide as a clarifier is used.

  In the homogenization step (ST4), the glass component is homogenized by stirring the molten glass in the stirring tank supplied through the pipe extending from the clarification tank using a stirrer. Thereby, the composition unevenness of the glass which is a cause of striae or the like can be reduced. One stirring tank or two or more stirring tanks may be provided. In the supplying step (ST5), the molten glass is supplied to the molding apparatus through a pipe extending from the stirring tank.

In the molding apparatus, a molding step (ST6) and a slow cooling step (ST7) are performed. In the forming step (ST6), the molten glass is formed into a sheet glass to make a flow of the sheet glass. For the molding, other methods such as an overflow downdraw method or a float method can be used.
In this embodiment, the overflow downdraw method is used. In the slow cooling step (ST7), the sheet glass that is formed and flows is cooled so that the thermal shrinkage rate, internal strain, and warpage are reduced (thermal shrinkage reduction process). Thus, in the manufacturing method of the glass substrate of this invention, it is preferable to perform a thermal contraction reduction process only by the online annealing which performs slow cooling in the slow cooling process (ST7) after sheet glass shaping | molding. The reason why it is preferable to perform the thermal shrinkage reduction process only by online annealing is that when the thermal shrinkage process is performed by offline annealing in which the heat treatment is performed again after cutting the sheet glass in the cutting step (ST8), a separate annealing furnace is required. is there. An annealing furnace is another furnace of the slow cooling furnace 202 of the shaping | molding apparatus mentioned later, for example. When the thermal shrinkage reduction treatment is performed by offline annealing, the thermal shrinkage rate can be reduced without adjusting the strain point to, for example, 680 ° C. or higher by adjusting the glass composition. However, such a method has a significantly low production efficiency.

  In the cutting step (ST8), in the cutting device, the sheet glass supplied from the forming device is cut into a predetermined length to obtain a plate-like glass plate. At this time, an ear | edge part is cut out from a sheet glass and a cullet produces | generates. The cut glass plate is further cut into a predetermined size to produce a glass substrate of a target size. After this, the end surface of the glass substrate is ground and polished, the glass substrate is cleaned, and further, the presence of abnormal defects such as bubbles and striae is inspected. Will be packed as.

(Control process)
Next, the control process will be described in more detail. In the control process, the β-OH value of the glass substrate is measured in the measurement process (ST9), and the cullet for the mixture of the glass raw material and the cullet is determined based on the measured β-OH value in the determination process (ST1). The blending ratio (cullet ratio) is determined.

(Measurement process)
In the measurement step, the β-OH value of the glass substrate cut to a predetermined length in the cutting step is obtained from the infrared absorption spectrum of the glass substrate obtained using a spectrophotometer according to the following equation. In addition, the frequency which measures the beta-OH value of a glass substrate is not specifically limited.
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 (%) at a hydroxyl group absorption wavelength of 2800 nm
The β-OH value is expressed in mm ⁻¹ . As the β-OH value, a value measured for the purpose of keeping the water content in the glass substrate within a certain amount so that bubbles are not generated in the glass substrate can be used. In other embodiments, the measurement step (ST9) may be performed not immediately after the cutting step (ST8) but immediately before the determination step performed before the melting step (ST2).

(Decision process)
In the determination step (ST1), based on the measured β-OH value of the glass substrate, the blending ratio (cullet ratio) of the cullet to the mixture of the glass raw material and the cullet is determined. At this time, the β-OH value of the cullet is measured in advance by the same method as the method for measuring the β-OH value of the glass substrate. In this way, the β-OH value of the glass substrate is measured, the cullet ratio is determined, and further, in the melting step (ST2), the glass raw material and the cullet are fed into the melting tank according to the determined cullet ratio, thereby providing feedback. Control is performed, and the β-OH value of the glass substrate is accurately controlled.

Next, the reason why the β-OH value of the glass substrate can be controlled by controlling the cullet ratio will be described.
The β-OH value in the glass substrate is mainly (1) Of the moisture contained in the glass raw material and cullet, the amount of moisture dissolved in the molten glass without being released out of the molten glass as gas bubbles in the melting step And (2) the amount of moisture dissolved in the molten glass from the atmosphere in contact with the molten glass liquid surface in the melting step through the molten glass liquid surface.
When the glass to be manufactured is a glass substrate for LTPS / TFT mounted display or a glass substrate for organic EL display having a low alkali metal oxide amount and a high melting temperature compared to soda lime glass, etc., melting in the above (2) The amount of moisture that dissolves in the glass increases. This is because in the production of glass having a high melting temperature, an oxygen gas burner having a high combustion efficiency and a high combustion efficiency is used as a gas burner used in the melting process, instead of an air combustion gas burner. Since the oxygen gas burner does not contain nitrogen that does not participate in combustion, instead of obtaining a high combustion temperature, the combustion exhaust gas contains a large amount of water vapor. That is, the amount of water that dissolves in the molten glass increases.
Here, since the cullet is once melted and vitrified, the cullet generally has a higher β-OH value than the glass raw material and the cullet. Therefore, by increasing the cullet ratio, the β-OH value of the produced glass substrate can be increased, and by reducing the cullet ratio, control such as lowering the β-OH value of the produced glass substrate can be achieved. It becomes possible.

  The cullet ratio is determined so that the β-OH value of the glass substrate becomes the target β-OH value based on the measured β-OH value. For example, the cullet ratio is preferably determined on the basis of the measured β-OH value, based on the change in production conditions and the change schedule that affect the β-OH value of the glass substrate. The target β-OH value can take various values. For example, based on the β-OH value of a glass substrate produced in the past, the amount of hydrate in the glass raw material and the amount of water in the liquid surface atmosphere May be determined with reference to FIG. The target β-OH value is preferably as low as possible from the viewpoint of reducing the absolute value of the heat shrinkage rate. The target β-OH value can be set to 0.35 / mm or less, for example. In the present embodiment, the cullet ratio is, for example, 20 to 30% by mass with respect to 100% by mass of the mixture of the glass raw material and cullet. In addition, a cullet ratio may be determined as a compounding ratio with respect to the mixture of a glass raw material and a cullet, and may be determined as a compounding ratio with respect to a glass raw material. In another embodiment, the determination step (ST1) is not performed immediately before the melting step (ST2), and may be performed subsequent to the measurement step (ST9) after the cutting step (ST8) in which the cullet is generated. Good. Further, the determination step (ST1) may be performed after a measurement step (ST9) with a time (for example, several days), and is performed immediately after the measurement step (ST9) and subsequently to the measurement step (ST9). It may be broken.

In addition, as a change or change of the manufacturing conditions affecting the β-OH value of the glass substrate described above, for example, a change of the glass raw material, a storage method of the glass raw material, a time during which the molten glass stays in the melting tank, in the melting step Examples thereof include a molten glass temperature, a gas burner gas used in the melting process, a gas burner / electric melting ratio, and the like. In addition, the β-OH value of the glass substrate can be reduced by changing the gas used in the gas burner to, for example, a gas having a long carbon chain (for example, propane gas instead of methane gas).
The above glass substrate manufacturing method can be performed using, for example, a glass substrate manufacturing apparatus described later. In that case, only a part of the steps of the glass substrate manufacturing method may be performed using the glass substrate manufacturing apparatus.

According to the manufacturing method of the glass substrate of this embodiment, the compounding ratio of the cullet to the mixture of the glass raw material and the cullet is controlled so that the β-OH value of the glass substrate becomes the target β-OH value. As a result, even if there is a change in manufacturing conditions that affect the β-OH value, for example, the variation in β-OH value for each glass substrate is reduced. Therefore, the variation of the strain point for each glass substrate is reduced, and the variation of the thermal shrinkage rate for each glass substrate is reduced. Moreover, the β-OH value of the glass substrate can be easily adjusted by controlling the mixing ratio of cullet.
In the method for manufacturing a glass substrate of another embodiment, other methods such as a slot down draw method, a float method, and a roll out method may be used instead of the overflow down draw method. Further, it is not always necessary to add cullet to the glass raw material, and the molten glass may be made using only the glass raw material.

(Glass substrate manufacturing equipment)
Next, a glass substrate manufacturing apparatus will be described.
FIG. 2 is a diagram schematically illustrating an example of an apparatus that performs the determination step (ST1) to the measurement step (ST9) in the present 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 tank 101, a clarification tank 102, a stirring tank 103, glass supply pipes 104, 105, 106, and a determination unit 116. The cutting device 300 includes a measuring unit 117. The control unit of the glass substrate manufacturing apparatus of the present invention includes a determination unit 116 and a measurement unit 117. A control part controls the compounding ratio of the cullet with respect to the mixture of a glass raw material and a cullet so that the β-OH value of the glass substrate becomes the target β-OH value. Specifically, the determination unit 116 and the measurement unit 117 determine the cullet ratio and measure the β-OH value prior to that.

In the melting tank 101 of the example shown in FIG. 2, the glass raw material and cullet are charged using a bucket 101d. A determination unit 116 is connected to the melting tank 101. The determination unit 116 determines the cullet ratio based on the β-OH value of the glass substrate measured by the measurement unit 117. In the clarification tank 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.
The forming apparatus 200 includes a forming furnace 201 and a slow cooling furnace 202, and a sheet glass SG is formed from the molten glass MG by an overflow down draw method using a formed body 210 disposed in the forming furnace 201.
The cutting device 300 cuts the sheet glass SG supplied from the forming device 200 into a predetermined size, and creates a glass substrate having a target size. At this time, cullet is generated. A measuring unit 117 is connected to the cutting device 300. The measuring unit 117 measures the β-OH value of the glass substrate.

According to the glass substrate manufacturing apparatus of the present embodiment, the cullet ratio relative to the mixture of the glass raw material and the cullet is controlled so that the β-OH value of the glass substrate becomes the target β-OH value, for example, β Even if there is a change in the production conditions affecting the —OH value, the variation in β-OH value for each glass substrate obtained is reduced. Therefore, the variation of the strain point for each glass substrate is reduced, and the variation of the thermal shrinkage rate for each glass substrate is reduced.
Moreover, the β-OH value of the glass substrate can be easily adjusted by controlling the mixing ratio of cullet.

(Glass substrate)
Here, the outline of the glass substrate manufactured with the manufacturing method and manufacturing apparatus of the glass substrate of this invention is demonstrated.
The thickness of the glass substrate is, for example, 0.1 to 1.5 mm.
The size of the glass substrate is, for example, 300 to 2500 mm × 400 to 3500 mm (length in the lateral direction × length in the longitudinal direction).

  As a glass plate for liquid crystal display and a glass plate for organic EL (Electro-Luminescence), a non-alkali glass substrate containing substantially no alkali metal oxide or an alkali trace glass substrate containing only 2% or less of alkali metal oxide Is preferably applied.

In addition, regarding the characteristics of the glass constituting the glass substrate, the temperature of the molten glass at a viscosity of 10 ^2.5 poise may be 1580 ° C. or higher, for example, 1590 to 1700 ° C. Further, the specific resistance of the glass constituting the glass substrate in the molten glass at 1550 ° C. may be 100 Ω · cm or more, and may be 100 to 350 Ω · cm, and may be 150 to 350 Ω · cm. it can. The higher the specific resistance, the more prominent the problem of melting of the melting tank described above. Incidentally, an attempt to increase the strain point of the glass substrate, there is a tendency that the specific resistance and the viscosity becomes high temperature of the molten glass in 10 ^2.5 poise.

A glass substrate consists of a composition shown below, for example. In the following composition ratios,% means mass%.
SiO _2: 50~70%,
Al ₂ O _3: 5~25%,
B ₂ O _3: 0~15%.
In addition, you may include arbitrarily the composition shown below.
MgO: 0 to 10%,
CaO: 0 to 20%,
SrO: 0 to 20%,
BaO: 0 to 10%,
ZrO _2: 0~10%.
Further, among the above compositions, in _{particular, SiO 2: 50~70%, B} 2 O 3: 5~18%, Al 2 O 3: 10~25%, MgO: 0~10%, CaO: 0~20 %, SrO: 0 to 20%, BaO: 0 to 10%, RO: 5 to 20% (wherein R is selected from Mg, Ca, Sr and Ba, and is all components contained in the glass substrate). It is preferable to contain.

Furthermore, R ′ ₂ O: more than 0% and 2.0% or less (provided that R ′ is all components contained in the glass substrate selected from Li, Na, and K). This can prevent the melting temperature from becoming excessively high even if the β-OH value is reduced. As the β-OH value of the glass substrate decreases, the strain point increases, so that the absolute value of the thermal contraction rate of the glass substrate can be decreased. Thereby, the variation in the thermal contraction rate of a glass substrate can also be reduced.

Furthermore, it is preferable that 0.05 to 1.5% of the refining agent is contained in total, and As ₂ O ₃ , Sb ₂ O ₃ and PbO are not substantially contained. This is because As ₂ O ₃ , Sb ₂ O ₃ and PbO are substances having an effect of clarifying glass, but are substances having a large environmental load. Here, “substantially not contained” means that the mass% is less than 0.01% and is not intentionally contained except for impurities. The fining agent preferably contains SnO ₂ The content of iron oxide in the glass is preferably 0.01 to 0.2%.

The following glass composition is mentioned as a glass composition of the glass substrate in which LTPS * TFT is formed. In the following composition ratios,% means mass%.
_{SiO 2: 52~78%, Al 2} O 3: 3~25%, B 2 O 3: 0~15%, RO ( where, R represents Mg, Ca, among Sr and Ba, all contained in the glass substrate Component): 3 to 20%, R ′ ₂ O (where R is all components contained in the glass substrate among Li, Na and K): 0.01 to 0.8%, Sb ₂ O ₃ : 0 0.3 mass%, As ₂ O ₃ is not substantially contained, the mass ratio CaO / RO is 0.65 or more, and the mass ratio (SiO ₂ + Al ₂ O ₃ ) / B ₂ O ₃ Is in the range of 7 to 30, and the mass ratio (SiO ₂ + Al ₂ O ₃ ) / RO is 5 or more. At this time, the strain point is preferably 688 ° C. or higher.

The β-OH value of the glass substrate is preferably 0.45 / mm or less, more preferably 0.35 / mm or less, further preferably 0.30 / mm or less, 0.25 / Mm or less is more preferable. This is because the smaller the β-OH value, the higher the strain point (viscosity increases) and the lower the heat shrinkage rate. On the other hand, if the β-OH value is forcibly lowered, the raw material price and manufacturing cost rise. Therefore, the β-OH value of the glass substrate is preferably 0 to 0.35 / mm, may be 0.05 to 0.35 / mm, and is 0.05 to 0.30 / mm. May be.
Further, according to the present invention, the variation of the β-OH value of the glass substrate can be maintained at ± 0.015 / mm or less, for example, and can be maintained at ± 0.01 / mm or less. Thus, by reducing the variation in the β-OH value, the variation in the thermal contraction rate for each glass substrate can be reduced.

  The strain point of the glass substrate is preferably 680 ° C. or higher, and more preferably 690 ° C. or higher in that the thermal shrinkage rate can be reduced. By setting the strain point to 680 ° C. or higher, the absolute value of the thermal contraction rate of the glass substrate can be reduced. Thereby, the variation in the thermal contraction rate of a glass substrate can also be reduced. The strain point is measured using, for example, a viscometer that measures the viscosity by a beam bending method.

  The thermal contraction rate of the glass substrate is, for example, 70 ppm or less. A glass substrate having such a low thermal shrinkage rate has high thermal stability and is particularly preferable as a glass substrate on which LTPS · TFT is formed. Moreover, when performing a thermal shrinkage reduction process only by online annealing, in order to suppress the enlargement of manufacturing equipment and cost, it is preferable that it is 10-70 ppm.

  A glass substrate is a glass substrate for flat panel displays. Examples of the flat panel display include a liquid crystal display, a plasma display, and an organic EL display. Especially, it is preferably used for a liquid crystal display or an organic EL display in that the variation in heat shrinkage can be reduced.

(Experimental example)
Hereinafter, experimental examples were shown to confirm the effects of the present invention.

The glass substrate was manufactured by the overflow down draw method by controlling the cullet ratio according to the method for manufacturing the glass substrate of the present invention described above. Specifically, the glass substrate is SiO ₂ ; 61.3 mass%, Al ₂ O ₃ ; 19.5 mass%, B ₂ O ₃ ; 9 mass%, CaO; 9.8 mass%, K ₂ O; 0 .15% by mass, Fe ₂ O ₃ ; 0.05% by mass, SnO ₂ ; with respect to a glass raw material prepared so as to contain 0.2% by mass, a cullet having a β-OH value of 0.24 / mm The cullet ratio was added to the melting tank at a ratio of 30% by mass. The composition of cullet was the same as that of the glass substrate. Moreover, the β-OH value of the glass substrate was 0.24 / mm, and the target β-OH value was 0.24 / mm. At this time, the strain point of the glass was 700 ° C., and the temperature when the viscosity was 10 ^2.5 poise was 1595 ° C.
Next, when the molten glass temperature in the melting step was increased by 20 ° C., one week later, the β-OH value of the glass substrate was 0.26 / mm, and the heat shrinkage rate was also increased by 2%. Therefore, a cullet ratio for reducing the β-OH value of the glass substrate by 0.02 / mm was calculated, and the cullet ratio to be introduced into the melting process was changed. Here, the cullet ratio was reduced from 30% by mass to 21% by mass with respect to 100% by mass of the mixture of the glass raw material and cullet. As a result, the β-OH value of the glass substrate could be 0.24 / mm. Moreover, the thermal contraction rate for every glass substrate was also equivalent to the glass substrate manufactured before raising the molten glass temperature about 20 degreeC.
Moreover, the β-OH value increase rate when the glass melting temperature in the melting process is increased by 20 ° C. is estimated in advance, and the cullet ratio is increased from 30% by mass to 21% by mass in accordance with the increase of the melting temperature by 20 ° C. Even when it was lowered, the β-OH value of the glass substrate could be maintained at 0.24 / mm, and the thermal shrinkage rate could be maintained.
In addition, the β-OH value and the heat shrinkage rate of the glass substrate and cullet were determined as follows.
In order to calculate the cullet ratio for lowering the β-OH value by a predetermined value, the contribution of the glass raw material to the glass substrate β-OH value (the gas contained in the glass raw material and the cullet, in the melting step, the gas It is preferable to measure in advance the amount of water dissolved in the molten glass without being discharged out of the molten glass as bubbles. For example, when the contribution of the glass raw material used in this experimental example is 0.023, the temperature operation of the molten glass leads to a β-OH value due to moisture dissolved in the glass from an atmosphere having a high water vapor concentration in the melting step. Can be calculated by the following equation (1). “Raw material ratio” is the compounding ratio of the glass raw material to the mixture of the glass raw material and cullet.
β-OH value = (contribution ratio of glass raw material × raw material ratio) + (caret β-OH value × caret ratio) + contribution X (1)
That is, in the said Example, the contribution X1 before molten glass temperature operation is 0.152, and the contribution X2 after molten glass temperature operation is 0.172, and has increased by 0.20. Therefore, in order to return the β-OH value to 0.24 / mm before the temperature operation of the molten glass, as shown in the following formula (2) obtained by adding a numerical value to the above formula (1), the cullet ratio C It is sufficient to set ≈0.21.
0.24 = (0.023 × (1-C)) + (0.24 × C) +0.172
(2)

(Β-OH value of glass substrate and cullet)
About the obtained glass substrate and cullet, (beta) -OH value was calculated | required according to the above-mentioned formula from the infrared absorption spectrum of the glass substrate using the Fourier-transform infrared spectrophotometer, respectively. The cullet used was cut from sheet glass when a glass substrate was manufactured in the past.

(Heat shrinkage)
The heat shrinkage rate was raised from room temperature at 10 ° C./min, held at 550 ° C. for 1 hour, then lowered to room temperature at 10 ° C./min, raised again at 10 ° C./min, and increased at 1 at 550 ° C. Using the shrinkage amount of the glass substrate after holding for a time and lowering to room temperature at 10 ° C./min, the following formula was used.
Thermal shrinkage (ppm) = {Shrinkage amount of glass before and after heat treatment / Glass length before heat treatment} × 10 ⁶

  As mentioned above, although the manufacturing method and manufacturing apparatus of the glass substrate of this invention 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, even if various improvement and a change are carried out. Of course it is good.

101 Melting tank 116 Control unit 201 Molding furnace ST1 Control process ST2 Melting process ST6 Molding process

Claims (7)

Melting process for melting glass raw material and cullet to make molten glass;
A method for producing a glass substrate for display, comprising producing a glass substrate having a strain point of 680 degrees or more, comprising a molding step of forming the molten glass into a sheet glass,
In order to reduce the variation of the strain point and the heat shrinkage rate for each glass substrate by setting the variation of β-OH value for each glass substrate to ± 0.015 / mm or less, β A control step of adjusting the β-OH value of the glass substrate by controlling the blending ratio of the cullet with respect to the mixture with the cullet having a high -OH value;
In the control step,
By determining the β-OH value of the manufactured glass substrate to determine the amount of change in β-OH value due to changes in manufacturing conditions,
Wherein the beta-OH value of the glass substrate, the so that the thermal shrinkage of the glass substrate becomes a predetermined target beta-OH value to be equal to or less than 70 ppm, based on the change amount of the beta-OH value Control the mixing ratio of cullet ,
The heat shrinkage rate is 10 ° C./min from room temperature, held at 550 ° C. for 1 hour, then lowered to room temperature at 10 ° C./min, raised again at 10 ° C./min, and heated at 550 ° C. Using the amount of shrinkage of the glass substrate after the heat treatment for holding for 1 hour and lowering to room temperature at 10 ° C./min, the following formula:
Thermal shrinkage rate (ppm) = {Shrinkage amount of glass substrate by heat treatment / Length of glass substrate before heat treatment} × 10 ⁶
Der Ru, method of manufacturing a glass substrate for a display, wherein the ones determined by.   The said glass substrate is a manufacturing method of the glass substrate for displays of Claim 1 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 for displays of Claim 1 or 2 which is a glass substrate for liquid crystal displays, or a glass substrate for organic EL displays. The method for producing a glass substrate for a display according to any one of claims 1 to 3 , wherein the blending ratio of the cullet is adjusted so that the blending ratio of the cullet is in a range of 20 to 30% by mass with respect to the mixture. . The melting step is performed using combustion heating performed using combustion means, and energization heating performed by passing a current through the molten glass,
Wherein as the ratio of the amount of heat generated by the combustion heat to the heating amount by the electrical heating is 1.5 or more 2.8 or less, performs the combustion heating and the conduction heat, according to any one of claims 1 4 Manufacturing method of glass substrate for display. The method for manufacturing a glass substrate for display according to claim 5 , wherein the combustion means is an oxygen gas burner. A melting tank for melting glass raw material and cullet to make molten glass;
A glass substrate manufacturing apparatus for manufacturing a glass substrate for display having a strain point of 680 degrees or more, and a molding furnace for forming the molten glass into a sheet glass,
In order to reduce the variation of the strain point and the heat shrinkage rate for each glass substrate by setting the variation of β-OH value for each glass substrate to ± 0.015 / mm or less, β A control unit for adjusting the β-OH value of the glass substrate by controlling the blending ratio of the cullet with respect to the mixture with the cullet having a high -OH value;
In the control unit,
By determining the β-OH value of the manufactured glass substrate to determine the amount of change in β-OH value due to changes in manufacturing conditions,
Wherein the beta-OH value of the glass substrate, the so that the thermal shrinkage of the glass substrate becomes a predetermined target beta-OH value to be equal to or less than 70 ppm, based on the change amount of the beta-OH value Control the mixing ratio of cullet ,
The heat shrinkage rate is 10 ° C./min from room temperature, held at 550 ° C. for 1 hour, then lowered to room temperature at 10 ° C./min, raised again at 10 ° C./min, and heated at 550 ° C. Using the amount of shrinkage of the glass substrate after the heat treatment for holding for 1 hour and lowering to room temperature at 10 ° C./min, the following formula:
Thermal shrinkage rate (ppm) = {Shrinkage amount of glass substrate by heat treatment / Length of glass substrate before heat treatment} × 10 ⁶
The Ru der ones determined, apparatus for manufacturing a glass substrate, characterized in that.

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