JP6964449B2 - Manufacturing method of glass substrate for display device and glass substrate manufacturing device for display device - Google Patents

Description

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

As a display device, for example, a liquid crystal panel used in a liquid crystal display device is mainly composed of two substrates and a liquid crystal material in between. More specifically, in the liquid crystal panel, a liquid crystal material is formed between a substrate in which a color filter is formed on a glass substrate and a substrate in which a semiconductor element such as a TFT (Thin Film Transistor) is formed on the glass substrate. It is manufactured by being sandwiched and the periphery of the substrate being sealed with a sealant.
In the process of manufacturing a liquid crystal panel, ultraviolet rays (wavelength 300 to 380 nm) are irradiated through a glass substrate. For example, ultraviolet rays (wavelength 300 to 380 nm) are irradiated through a glass substrate to perform lithography and sealing around the substrate with an ultraviolet curable resin. Further, a method of irradiating ultraviolet rays through a glass substrate to polymerize a photopolymerizable polymer in a liquid crystal material to stabilize the orientation of liquid crystal molecules is also used. In recent years, among the wavelengths of 300 to 380 nm, ultraviolet rays having a wavelength of around 300 nm are often used, and it is particularly desired to improve the ultraviolet transmittance in the vicinity of wavelength of 300 nm.

It is known that the ultraviolet transmittance in the vicinity of a wavelength of 300 nm ^{decreases when the amount of trivalent iron ions (Fe 3+} ) contained in the glass substrate is large (for example, Patent Document 1). Therefore, it is considered effective to manufacture a glass substrate having a small amount of _{Fe 2} O ₃ as a glass substrate for a liquid crystal display device.

International Publication No. 2012/132449

However, the glass raw material often contains iron oxide as an impurity. Moreover, since iron oxide is accompanied by valence fluctuations in the manufacturing process of the glass substrate, it is difficult to control the amount _{of Fe 2} O _{3 in the glass substrate. Further, the permissible amount of Fe 2} O ₃ in the glass substrate, which does not reduce the ultraviolet transmittance in the vicinity of the wavelength of 300 nm, is extremely small. Therefore, depending on the amount of iron oxide contained in the glass raw material, the allowable amount that does not reduce the ultraviolet transmittance may be exceeded, and the ultraviolet transmittance in the vicinity of the wavelength of 300 nm may decrease.

The present invention is intended to provide a method for manufacturing a glass substrate for a display device having a high transmittance of light having a wavelength of 300 nm, and a method for manufacturing a glass substrate for a display device.

The present invention provides the following (1) to ( 5 ).

(1) A method for manufacturing a glass substrate for a display device.
The melting process of melting glass raw materials containing iron oxide to make molten glass,
A stirring step of stirring while flowing the molten glass in a stirring tank,
Prior to the stirring step, a clarification step of clarifying the molten glass is provided.
The molten glass produced in the melting step _{contains SnO 2} and contains SnO 2.
The concentration ratio [Sn ⁴⁺ ] / [Sn ^{2+ ] of Sn 4+} and Sn ²⁺ contained in the molten glass that is agitated in the stirring step is 1 or more.
_{In the stirring step, the Fe 2} O ₃ content in the molten glass is adjusted by adjusting the length of time that the molten glass is maintained at a temperature of 1400 ° C. or higher in the stirring tank. A method for manufacturing a glass substrate for a display device, which comprises setting the transmittance of light having a wavelength of 300 nm in the glass substrate for a display device to 30% or more.

(2) In the stirring step, the temperature of the stirring tank portion located on the upstream side in the flow direction of the molten glass is higher than the temperature of the stirring tank portion located on the downstream side in the flow direction. The method for manufacturing a glass substrate for a display device according to (1) above, wherein the length of time is adjusted by adjusting the temperature of the stirring tank.

(3) In the stirring step, using a plurality of containers connected to each other in the flow direction as the stirring tank, stirring is performed in each of the containers.
The first container and the second container so that the temperature of the first container located on the upstream side in the flow direction of the molten glass is higher than the temperature of the second container located on the downstream side in the flow direction. The method for manufacturing a glass substrate for a display device according to (1) above, wherein the length of time is adjusted by adjusting the temperature of the container.

( 4 ) In the stirring step, when the length of the time is referred to as the length of the first time, it is longer than the length of the second time in which the molten glass is maintained at a temperature of less than 1400 ° C. in the stirring tank. The method for manufacturing a glass substrate for a display device according to any one of (1) to (3 ) above, which increases the length of the first time.

( 5 ) A glass substrate manufacturing device for display devices.
A melting tank that melts glass raw materials containing iron oxide to make molten glass,
A clarification tube for clarifying the molten glass and
In the stirring tank, a stirring device for stirring while flowing the clarified molten glass is provided.
The molten glass made in the melting tank _{contains SnO 2} and contains SnO 2.
The concentration ratio [Sn ⁴⁺ ] / [Sn ^{2+ ] of Sn 4+} and Sn ²⁺ contained in the molten glass that is agitated in the stirring tank is 1 or more.
The stirring device adjusts the length of time that the molten glass is maintained at a temperature of 1400 ° C. or higher in the stirring tank to adjust the content _{of Fe 2} O _{3 in the molten glass.} the Viewing transmittance of light of the apparatus 300nm wavelength of the glass substrate to 30% or more, the display device glass substrate manufacturing apparatus characterized by.

According to the present invention, it is possible to manufacture a glass substrate having a high transmittance of light having a wavelength of 300 nm.

It is a flow chart which shows the manufacturing method of the glass substrate for a display device. It is the schematic of the glass substrate manufacturing apparatus for a display device. It is the schematic of the modification of the glass substrate manufacturing apparatus for a display device. It is a graph which shows the relationship between the ultraviolet transmittance and the wavelength of the glass substrate for a display device.

Hereinafter, a method for manufacturing a glass substrate for a display device (hereinafter, simply referred to as a glass substrate) and a glass substrate manufacturing device for a display device (hereinafter, simply referred to as a glass substrate manufacturing device) of the present embodiment will be described.
(Overview of manufacturing method of glass substrate)
FIG. 1 is a diagram showing an example of a process of the method for manufacturing a glass substrate of the present embodiment. The glass substrate manufacturing method includes a melting step (ST1), a clarification step (ST2), a stirring step (ST3), a molding step (ST4), a slow cooling step (ST5), a cutting step (ST6), and an inspection step (ST7). ) Mainly. In addition to this, it may have a grinding process, a polishing process, a cleaning process, a packing process, and the like. The manufactured glass substrates are laminated in the packaging process as needed and transported to the supplier.

In the melting step (ST1), molten glass is produced by heating a glass raw material. The glass raw material contains iron oxide. Iron oxide may be contained as an impurity in the glass raw material, or may be contained as a clarifying agent.
In the clarification step (ST2), the temperature of the molten glass is raised to generate bubbles containing _{oxygen, CO 2} or SO _{2 contained in the molten glass.} The bubbles absorb oxygen generated by the reduction reaction of a clarifying agent (tin oxide or the like) contained in the molten glass, grow, and float on the liquid surface of the molten glass and are released. After that, in the clarification step, the temperature of the molten glass is lowered to promote the oxidation reaction of the reducing substance produced by the reduction reaction of the clarifying agent. As a result, gas components such as oxygen in the bubbles remaining in the molten glass are reabsorbed in the molten glass, and the bubbles disappear.

In the stirring step (ST3), after the clarification step (ST2), the molten glass is stirred with a stirrer to homogenize the glass components. This makes it possible to reduce the uneven composition of the glass, which is a cause of veins and the like. The stirring step is performed while flowing molten glass in a stirring tank described later. The homogenized molten glass is supplied to the molding apparatus. The stirring step (ST3) will be described in detail later.

The molding step (ST4) and the slow cooling step (ST5) are performed by a molding apparatus.
In the molding step (ST4), the molten glass is molded into a sheet glass which is a strip-shaped glass having a predetermined thickness to create a flow of the sheet glass. Float method, fusion method (overflow down draw method), etc. are used for molding, but since it is difficult to lengthen the slow cooling device on the production line by the fusion method, glass including offline heat treatment (described later). The fusion method is suitable as a method for manufacturing a substrate.
In the slow cooling step (ST5), the molded and flowing sheet glass has a desired thickness and is cooled so as not to cause internal strain and further to prevent warpage.
In the cutting step (ST6), a plate-shaped glass substrate is obtained by cutting the sheet glass after slow cooling to a predetermined length. Cutting the sheet glass into a base plate of a predetermined length is also called plate picking. The glass substrate obtained by the plate sampling is further cut into a predetermined size to produce a glass substrate having a target size.

In the cutting step (ST6), the glass substrate obtained by the plate sampling may be guided and conveyed to a furnace for which the heat treatment step is performed while being pinched by, for example, a transfer mechanism (not shown), and the heat treatment may be performed. The glass substrate after plate-cutting or heat treatment is further conveyed to a cutting device and cut to the size of a product to obtain a glass substrate. For the glass substrate obtained by the cutting step (ST6), for example, the following steps are performed.
In the grinding and polishing steps, end face processing including grinding, polishing and corner cutting of the end face of the glass substrate is performed. The glass substrate after the end face processing is cleaned (primary cleaning) in order to remove fine foreign matter and dirt on the glass surface in the cleaning process. After the primary cleaning, for example, the glass substrate is subjected to surface treatment including a roughening step and a rinsing step. After the surface treatment, the glass substrate is further cleaned (secondary cleaning).

In the inspection step (ST7), an optical inspection is performed for scratches, dust, dirt, scratches including optical defects, and for foreign matter. Further, in the inspection step (ST7), the ultraviolet transmittance in the vicinity of the wavelength of 300 nm may be measured. In the packing process, the glass substrate having the quality conformed by the inspection is loaded on the pallet and packed as a laminated body alternately laminated with the paper protecting the glass substrate. The packed glass substrate is shipped to the supplier.

(Overview of glass substrate manufacturing equipment)
FIG. 2 is a schematic view of a glass substrate manufacturing apparatus that performs the melting step (ST1) to the cutting step (ST6) in the present embodiment. As shown in FIG. 2, the glass substrate manufacturing apparatus mainly includes a melting apparatus 100, a forming apparatus 200, and a cutting apparatus 300. The melting device 100 includes a melting tank 101, a clarification pipe 102, a stirring tank 130, transfer pipes 104 and 105, and a glass supply pipe 106.
The melting tank 101 shown in FIG. 2 is provided with a heating means such as a burner (not shown). The glass raw material to which the clarifying agent is added is put into the melting tank 101, and the melting step (ST1) is performed. The molten glass melted in the melting tank 101 is supplied to the clarification pipe 102 via the transfer pipe 104.
In the clarifying tube 102, the temperature of the molten glass MG is adjusted while flowing the molten glass MG, and the clarification step (ST2) of the molten glass is performed by utilizing the redox reaction of the clarifying agent. Specifically, when the temperature of the molten glass in the clarifying tube 102 is raised _{, the bubbles containing oxygen, CO 2} or SO ₂ contained in the clarifying glass absorb the oxygen generated by the reduction reaction of the clarifying agent. It grows and floats on the liquid surface of the molten glass and is released into the gas phase space. After that, by lowering the temperature of the molten glass, the reducing substance produced by the reduction reaction of the clarifying agent undergoes an oxidation reaction. As a result, gas components such as oxygen in the bubbles remaining in the molten glass are reabsorbed in the molten glass, and the bubbles disappear. The clarified molten glass is supplied to the stirring tank 130 via the transfer pipe 105.
In the stirring tank 130, the molten glass is stirred by the stirrer 131 to perform the stirring step (ST3). The molten glass homogenized in the stirring tank 130 is supplied to the molding apparatus 200 via the glass supply pipe 106. The stirring tank 130 is heated by, for example, a heating means such as a heater, which will be described later, arranged around the stirring tank 130.
In the molding apparatus 200, the sheet glass SG is molded from the molten glass (molding step ST4) and slowly cooled (slow cooling step ST5) by, for example, an overflow down draw method.
In the cutting device 300, a plate-shaped glass substrate cut out from the sheet glass SG is formed (cutting step ST6).

(Overview of glass substrate)
Here, the glass substrate manufacturing method of the present embodiment or the glass substrate manufactured by the glass substrate manufacturing apparatus will be described.
The glass substrate is a glass substrate used for display devices such as liquid crystal display devices and organic EL display devices. When used in a liquid crystal display device, it is used as two glass substrates sandwiching a liquid crystal material of a liquid crystal panel. When used for an organic EL, it is used as a glass substrate arranged on the side of the anode constituting the light emitting element. Further, the glass substrate is used for high-definition displays such as oxide semiconductor displays using oxide semiconductors such as IGZO (indium, gallium, zinc, oxygen) and LTPS displays using LTPS (low temperature polysilicon) semiconductors. It may be a thing. Further, the glass substrate may be used for a display device such as a flat panel display or a curved panel display.
The size of the glass substrate is not particularly limited, but 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, and preferably 2000 mm to 3500 mm, respectively.
The thickness of the glass substrate is, for example, 0.1 to 1.1 mm, more preferably 0.75 mm or less, 0.55 mm or less, and further 0.45 mm or less. The lower limit of the thickness of the glass substrate is preferably 0.15 mm, more preferably 0.25 mm.
Further, the transmittance of the glass substrate is 30% or more at a wavelength of 300 nm. Here, when the transmittance of the wavelength of 300 nm is 30% or more, the transmittance of light having a wavelength of 300 nm is 30% in the range of 0.1 to 1.1 mm in thickness of the glass substrate, regardless of the thickness. That is all. The transmittance of the glass substrate is set to the above value at the stage of manufacturing a liquid crystal panel or an organic EL panel by irradiating it with ultraviolet rays having a wavelength of 300 nm, for example, sealing a liquid crystal material or an organic EL material. This is because the process of polymerizing the photopolymerized polymer in the liquid crystal material and stabilizing the orientation of the liquid crystal molecules is efficiently performed.

Examples of the glass substrate include aluminum noborosilicate glass having the composition shown below. The numerical values shown in parentheses below are preferable composition ratios. The% indication of the composition ratio below means mass%.
SiO ₂ : 50-70% (55-68%, 58-62%),
Al ₂ O ₃ : 10 to 25% (15 to 20%, 15 to 18%),
B ₂ O ₃ : 4-18% (6-14%, 10-13%),
MgO: 0-10% (0-5%, 1-2%),
CaO: 0-20% (1-10%, 4-7%),
SrO: 0 to 20% (0 to 10%, 1 to 3%),
BaO: 0-10% (0-2%, 0-1%),
K ₂ O: 0 to 2% (0.1 to 2%, 0.1 to 0.5%),
SnO ₂ : 0 to 1% (0.01 to 0.5%, 0.05 to 0.4%, 0.1 to 0.3%, 0.15 to 0.25%),
Fe ₂ O ₃ : 0.01 to 0.045% (0.015 to 0.04%, 0.02 to 0.035%).

Further, for example, aluminoborosilicate glass having the composition shown below can be mentioned.
SiO ₂ : 60-80% (65-78%, 68-73%),
Al ₂ O ₃ : 5 to 20% (8 to 18%, 12 to 18%),
B ₂ O ₃ : 0-10% (0-8%, 0-6%),
MgO: 0-10% (0-7%, 0-1%),
CaO: 0-20% (2-12%, 3-10%),
SrO: 0 to 20% (0 to 10%, 0 to 1%),
BaO: 0-10% (0-2%, 0-1%),
K ₂ O: 0 to 2% (0.1 to 2%, 0.1 to 0.5%),
SnO ₂ : 0 to 1% (0.01 to 0.5%, 0.05 to 0.4%, 0.1 to 0.3%, 0.15 to 0.25%),
Fe ₂ O ₃ : 0.01 to 0.045% (0.015 to 0.04%, 0.02 to 0.035%).

Here, the content of Fe ₂ O ₃ is (in terms of the) value expressed in Fe ₂ O ₃ in total oxides such as Fe ²⁺ and Fe ^3+. As _{the content of Fe 2} O ₃ increases, the ultraviolet transmittance decreases. Therefore, in the manufactured glass substrate, the content rate (mass%) of _{Fe 2} O _{3 is limited to a predetermined range.} The content of Fe ₂ O ₃ is preferably 0.02% by mass or less, and more preferably 0.015% by mass or less.
Here, _{it is preferable to set SnO 2} to 0.15 to 0.25% from the viewpoint of improving the transmittance of ultraviolet rays. By including 0.15 to 0.25% by mass of SnO ₂ in the glass substrate, the glass can be sufficiently clarified and a glass substrate having a transmittance of 30% or more at a wavelength of 300 nm can be produced.

In the measurement of the transmittance of ultraviolet rays, the manufactured glass substrate is cut to prepare a substantially square glass sample having a side of 30 mm. The transmittance referred to in the present invention is a value obtained by measuring the transmittance when the glass specimen is irradiated with light having a wavelength of 200 nm to 800 nm using a spectrophotometer. As the spectrophotometer, for example, "UV-3100PC" manufactured by Shimadzu Corporation is used.

Such a glass substrate _{contains a silica raw material containing SiO 2} as a main component (a component of _{98% by mass or more), and alumina and CaCO 3 containing Al 2} O ₃ as a main component (a component of 98% by mass or more). Manufactured using raw materials such as limestone as the main component (90% by mass or more). Examples of the silica raw material include silica sand. The silica raw material, _{alumina containing Al 2} O ₃ as a main _{component, limestone containing CaCO 3} as a main component, and the like contain a small amount of iron oxide as an impurity. The impurity is not a component that is intentionally contained, but a component that is unintentionally contained in an amount of 0.5% by mass or less with respect to the raw material.

(Stirring process)
Next, the stirring step (ST3) will be described in detail.
_{In the stirring step (ST3), Fe 2} O in the molten glass is adjusted by adjusting the length of time that the molten glass is maintained at a temperature of 1400 ° C. or higher in the stirring tank (the residence time of the molten glass in the stirring tank). _{By adjusting the content of 3} , the transmission rate of light (ultraviolet light) having a wavelength of 300 nm on the glass substrate is increased to 30% or more. According to the study of the present inventor, there is a correlation between the transmittance of ultraviolet rays having a wavelength of 300 nm and the temperature change (temperature profile) of the molten glass during the manufacturing method of the glass substrate, particularly, 1400 ° C. It was revealed that there is a correlation between the temperature profile of the molten glass in the vicinity and the transmittance of ultraviolet rays having a wavelength of 300 nm. In the method for manufacturing a glass substrate, the temperature of the molten glass is generally set to around 1400 ° C. in the stirring step. _{The lower the content of Fe 2} O ₃ in the molten glass, the higher the transmittance of ultraviolet rays having a wavelength of 300 nm. Based on these facts and the above correlation, the present inventor can adjust the content _{of Fe 2} O ₃ in the molten glass by adjusting the residence time of the molten glass in the stirring tank, whereby the content of Fe 2 O 3 in the molten glass can be adjusted. It has been found that the transmittance of light having a wavelength of 300 nm on a glass substrate can be set to 30% or more (for example, 40% or more, 50% or more). Incidentally, the content of Fe ₂ O ₃ refers to the content of Fe ₂ O ₃ contained in molten glass even after the stirring step (ST3).
The glass raw material often contains iron oxide as an impurity, and depending on the amount of iron oxide contained in the glass raw material, the ultraviolet transmittance in the vicinity of a wavelength of 300 nm may decrease. According to the method for producing a glass substrate of the present embodiment, the amount of iron oxide contained in the glass raw material exceeds an allowable range (for example, 0.045% by mass or less) that does not reduce the ultraviolet transmittance in the vicinity of a wavelength of 300 nm. Even so, the transmittance of ultraviolet rays having a wavelength of 300 nm can be increased to 30% or more by adjusting the residence time of the molten glass in the stirring tank to adjust _{the content of Fe 2} O _{3 in the molten glass.} can. Therefore, for example, when manufacturing a liquid crystal panel of a liquid crystal display device or an organic EL panel of an organic EL display device using the obtained glass substrate, ultraviolet rays having a wavelength of 300 to 380 nm, particularly 300 to 350 nm, are emitted to the glass substrate. When irradiated, lithography and sealing around the substrate with an ultraviolet curable resin can be preferably performed. In particular, when manufacturing a liquid crystal panel, it is possible to preferably stabilize the orientation of the liquid crystal molecules.

The time for the molten glass to pass through the stirring tank is almost constant regardless of the glass composition. Therefore, the staying time of the molten glass in the stirring tank can be adjusted by increasing the ratio of the time during which the molten glass passes through the stirring tank to the time maintained at 1400 ° C. or higher as compared with the conventional case. ..
Specifically, such adjustment of the residence time is performed by forming a temperature distribution according to the region of the stirring tank along the flow direction of the molten glass. For example, a plurality of heating means are arranged around the stirring tank 130 shown in FIG. 2 along the direction in which the molten glass moves, and the heating amount of the stirring tank 130 by these heating means is controlled. A temperature distribution can be created according to the region of the stirring tank 130. As the heating means, for example, heaters 140a and 140b arranged in an electric furnace in which the stirring tank 130 is arranged are used. The temperature of the molten glass is lowered from the clarification step (ST2) to the molding step (ST5). Further, according to the study by the present inventor, it has been found that the region on the downstream side of the stirring tank has a higher correlation between the temperature of the molten glass and the ultraviolet transmittance in the vicinity of the wavelength of 300 nm. In the present embodiment, for example, the temperature of the stirring tank 130 is adjusted so that the temperature of the upstream portion of the stirring tank 130 is higher than the temperature of the downstream portion of the stirring tank 130. More specifically, the heater 140a arranged around the upstream portion 130a is controlled to maintain the temperature of the molten glass flowing through the upstream portion at 1400 ° C. or higher, and the heater arranged around the downstream portion The temperature of the molten glass flowing in the downstream portion is controlled to be less than 1400 ° C. by controlling 140b. In this way, the temperature distribution can be created according to the region of the stirring tank 130. In the stirring tank 130 shown in FIG. 2, the molten glass moves from the upper side to the lower side while being stirred by the stirrer 131.
Such setting of the temperature distribution of the stirring tank 130 is performed before the method for manufacturing the glass substrate (before the operation).

In the adjustment of the staying time described above, the temperature of the molten glass flowing in the downstream portion of the stirring tank 130 may be maintained at 1400 ° C. or higher. That is, the temperature of the molten glass may be maintained at 1400 ° C. or higher in the entire stirring tank 130. The ratio of the lengths of the upstream portion and the downstream portion of the stirring tank 130 along the flow direction of the molten glass is, for example, 1: 0 to 1: 1.

In the example shown in FIG. 2, the molten glass is supplied from the transfer pipe 105 to the upper part of the stirring tank 130, and the molten glass flows from the lower part of the stirring tank 130 to the glass supply pipe 106. On the contrary, the molten glass may be supplied from the transfer pipe 105 to the lower part of the stirring tank 130, and the molten glass may flow from the upper part of the stirring tank 130 to the glass supply pipe 106.

The staying time of the molten glass in the stirring tank may be adjusted by using the stirring tank 130 shown in FIG. FIG. 3 is a schematic view of a modified example of the glass substrate manufacturing apparatus. In FIG. 3, the elements of the glass substrate manufacturing apparatus other than the stirring tank 130 are configured in the same manner as the corresponding elements shown in FIG.
The stirring tank 130 shown in FIG. 3 includes a first container 130A and a second container 130B connected to each other in the flow direction. The first container 130A has a first stirrer 131A. The second container 130B has a second stirrer 131B. In the stirring tank 130 shown in FIG. 3, the molten glass is homogenized by stirring in the first container 130A and the second container 130B, respectively.
The upper parts of the first container 130A and the second container 130B are connected to each other by a transfer pipe 133.
The molten glass is supplied to the first container 130A from the lower part by the transfer pipe 105. The molten glass rises in the first container 130A while being agitated by the first stirrer 131A. The molten glass that has reached the upper part of the first container 130A is transferred to the upper part of the second container by the transfer pipe 133.
The second container 130B is supplied with molten glass from above by a transfer pipe 133. The molten glass descends in the second container 130B while being agitated by the second stirrer 131B. The molten glass that has reached the lower part of the second container 130B is transferred to the molded body of the molding apparatus 200 by the glass supply pipe 106.

In the modified example shown in FIG. 3, a plurality of heating means are arranged around the first container 130A, the transfer pipe 133, and the second container 130B along the direction in which the molten glass moves, and heating these means. The temperature distribution of the stirring tank 130 can be created by controlling the heating amount of the stirring tank 130 by means. As the heating means, for example, a heater in an electric furnace in which the first container 130A, the transfer pipe 133, and the second container 130B are arranged inside can be used. In this modification, specifically, the heater 140A arranged around the first container 130A is controlled to maintain the temperature of the molten glass flowing through the temperature of the first container 130A at 1400 ° C. or higher, and the second The heater 140B arranged around the container 130B is controlled so that the temperature of the molten glass flowing through the second container 130B is less than 1400 ° C. In this way, the temperature distribution can be created according to the region of the stirring tank 130.
Since the time for the molten glass to pass through the transfer pipe 133 is shorter than the time for passing through the first container 130A and the second container 130B, the staying time of the molten glass in the stirring tank 130 is the first. It can be regarded as equal to the total time of passing through the container 130A and the second container 130B.

In the modified example shown in FIG. 3, the adjustment of the staying time of the molten glass in the stirring tank is not limited to the above-mentioned method, and is, for example, on the upstream side of the first container 130A and the second container 130B. The temperature of the molten glass flowing through the located portion is maintained at 1400 ° C. or higher, and the temperature of the molten glass flowing through the portion located on the downstream side of the second container 130B is set to less than 1400 ° C. to reduce the temperature of the stirring tank 130. The temperature of the stirring tank 130 may be adjusted by maintaining the temperature of the molten glass at 1400 ° C. or higher in the entire first container 130A and the second container 130B.

In the stirring step (ST3), in _{order to enhance the effect of reducing the content of Fe 2} O ₃ in the molten glass, the length t1 of the time for maintaining the temperature of the molten glass at 1400 ° C. or higher in the stirring tank is stirred. It is preferable that the temperature of the molten glass in the tank is made longer than t2, that is, t1 / t2 is made larger than 1. Examples of the preferred range of t1 / t2 are 1-3. On the other hand, t1 / t2 may be less than 1.

When the molten glass stirred in the stirring step (ST3) _{contains tin oxide (SnO 2} ) as a clarifying agent, the concentration ratio of ^{Sn 4+} and Sn ²⁺ contained in the molten glass ^{[Sn 4+} ] / It is preferable that [Sn ²⁺ ] is 1 or more. In a molten glass having such a concentration ratio _{, an oxidation reaction from FeO to Fe 2} O ₃ is unlikely to occur. Therefore, by adjusting the staying time of the molten glass in the stirring tank, Fe ₂ O _{3 in the molten glass is adjusted.} The effect of reducing the content of The concentration ratio [Sn ⁴⁺ ] / [Sn ²⁺ ] refers to the concentration ratio at the time when the molten glass is supplied from the clarification tube to the stirring tank. The molten glass having a concentration ratio [Sn ⁴⁺ ] / [Sn ²⁺ ] of 1 or more is, for example, the molten glass immediately after the above-mentioned reabsorption is performed in the clarification step (ST2). Therefore, in the melting step (ST1), it is preferable to produce molten glass containing _{SnO 2 as a clarifying agent.}

In the stirring step (ST3), it is preferable to control the temperature of the molten glass when adjusting the staying time. If the temperature of the molten glass in the stirring tank is too high, the viscosity of the molten glass becomes low, and the cooling in the glass supply pipe 106 becomes insufficient. Therefore, it becomes difficult to mold the sheet glass SG in the molding step (ST4). Further, if the temperature of the molten glass in the stirring tank is too low, the viscosity of the molten glass becomes high and it becomes difficult to stir. Therefore, the homogenization of the molten glass becomes insufficient. Therefore, when adjusting the staying time in the stirring step (ST3), it is preferable that the upper limit of the temperature of the molten glass is 1480 ° C. when the temperature of the molten glass is maintained at 1400 ° C. or higher. When the temperature of the glass is less than 1400 ° C, the lower limit of the temperature of the molten glass is preferably 1380 ° C.

_{According to the present embodiment, the content of Fe 2} O ₃ in the molten glass can be adjusted by adjusting the residence time of the molten glass in the stirring tank, whereby the light having a wavelength of 300 nm on the glass substrate can be adjusted. The transmittance can be 30% or more.
Further, in the stirring step (ST3), in _{order to enhance the effect of reducing the content of Fe 2} O ₃ in the molten glass, the length t1 of the time for maintaining the temperature of the molten glass at 1400 ° C. or higher in the stirring tank is set. It is preferable that the temperature of the molten glass is made longer than t2, which is the length of time for keeping the temperature of the molten glass less than 1400 ° C. in the stirring tank.
Further, when tin oxide (SnO ₂ ) is contained as a clarifying agent, the concentration ratio [Sn ⁴⁺ ] / [Sn ^{2+ ] of Sn 4+} and Sn ²⁺ contained in the molten glass is 1 or more. , The oxidation reaction from FeO to Fe ₂ O ₃ is unlikely to occur. Therefore, by adjusting the staying time of the molten glass in the stirring tank, the effect of reducing the content _{of Fe 2} O _{3 in the molten glass is enhanced.}

(Experimental example)
Using the stirring tank shown in FIG. 3, a glass substrate was produced according to the method for producing a glass substrate of the above embodiment, and the ultraviolet transmittance at a wavelength of 300 nm was examined. The manufactured glass substrate is an aluminum noborosilicate glass substrate containing 0.015 to 0.04% by mass of _{Fe 2} O _3. In the stirring step (ST3), the temperature of the molten glass is maintained at 1400 ° C. or higher in the first container 130A, and the temperature of the molten glass is kept below 1400 ° C. in the second container 130B. Made adjustments. When a glass specimen cut out from a glass substrate was irradiated with light having a wavelength of 200 to 800 nm, the transmittance was measured using a spectrophotometer. As a result, the absorption peak shown in FIG. 4 was obtained, and the transmittance was high at a wavelength of 300 nm. It was confirmed that it was 30% or more (75%). FIG. 4 is a graph showing the relationship between the ultraviolet transmittance and the wavelength of the glass substrate.

Although the method for manufacturing a glass substrate for a display device and the glass substrate manufacturing device for a display device of the present invention have been described in detail above, the present invention is not limited to the above-described embodiment and is not deviated from the gist of the present invention. Of course, various improvements and changes may be made.

100 Melting device 101 Melting tank 102 Clarifying pipe 104, 105 Transfer pipe 106 Glass supply pipe 130 Stirring tank 131a Upstream side 131b Downstream part 131A First container 131B Second container 131 Stirrer 140 Heater 200 Molding device 300 Cutting device

Claims (5)

A method for manufacturing glass substrates for display devices.
The melting process of melting glass raw materials containing iron oxide to make molten glass,
A stirring step of stirring while flowing the molten glass in a stirring tank,
Prior to the stirring step, a clarification step of clarifying the molten glass is provided.
The molten glass produced in the melting step _{contains SnO 2} and contains SnO 2.
The concentration ratio [Sn ⁴⁺ ] / [Sn ^{2+ ] of Sn 4+} and Sn ²⁺ contained in the molten glass that is agitated in the stirring step is 1 or more.
_{In the stirring step, the Fe 2} O ₃ content in the molten glass is adjusted by adjusting the length of time that the molten glass is maintained at a temperature of 1400 ° C. or higher in the stirring tank. A method for manufacturing a glass substrate for a display device, which comprises setting the transmittance of light having a wavelength of 300 nm in the glass substrate for a display device to 30% or more. In the stirring step, a plurality of containers connected to each other in the flow direction are used as the stirring tank, and stirring is performed in each of the containers.
The first container and the second container so that the temperature of the first container located on the upstream side in the flow direction of the molten glass is higher than the temperature of the second container located on the downstream side in the flow direction. The method for manufacturing a glass substrate for a display device according to claim 1, wherein the length of time is adjusted by adjusting the temperature of the container. In the stirring step, the stirring tank is set so that the temperature of the stirring tank portion located on the upstream side in the flow direction of the molten glass is higher than the temperature of the stirring tank portion located on the downstream side in the flow direction. The method for manufacturing a glass substrate for a display device according to claim 1, wherein the length of time is adjusted by adjusting the temperature of the above. In the stirring step, when the length of the time is referred to as the length of the first time, the first time is longer than the length of the second time in which the molten glass is maintained at a temperature of less than 1400 ° C. in the stirring tank. The method for manufacturing a glass substrate for a display device according to any one of claims 1 to 3 , wherein the length of time is increased. It is a glass substrate manufacturing device for display devices.
A melting tank that melts glass raw materials containing iron oxide to make molten glass,
A clarification tube for clarifying the molten glass and
In the stirring tank, a stirring device for stirring while flowing the clarified molten glass is provided.
The molten glass made in the melting tank _{contains SnO 2} and contains SnO 2.
The concentration ratio [Sn ⁴⁺ ] / [Sn ^{2+ ] of Sn 4+} and Sn ²⁺ contained in the molten glass that is agitated in the stirring tank is 1 or more.
The stirring device adjusts the length of time that the molten glass is maintained at a temperature of 1400 ° C. or higher in the stirring tank to adjust the content _{of Fe 2} O _{3 in the molten glass.} the Viewing transmittance of light of the apparatus 300nm wavelength of the glass substrate to 30% or more, the display device glass substrate manufacturing apparatus characterized by.

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