JP5668066B2 - Manufacturing method of glass substrate - Google Patents

Description

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

  For example, glass substrates used for flat panel displays (hereinafter referred to as FPD) such as liquid crystal displays and plasma displays are mainly 0.5 to 0.7 mm in thickness and 300 to 400 mm to 2850 to 3050 mm in size. is there.

  An overflow down draw method is known as a method for manufacturing a glass substrate for FPD. In the overflow down-draw method, in a forming furnace, the molten glass is made to overflow from the upper part of the molded body of the molten glass, whereby the sheet glass is formed from the molten glass, and the formed sheet glass is gradually cooled and cut. Thereafter, the cut sheet glass is further cut into a predetermined size according to customer specifications, subjected to cleaning, end face polishing, etc., and shipped as a glass substrate for FDP.

Among the glass substrates for FPD, in particular, the glass substrate for liquid crystal display devices has a semiconductor element formed on the surface thereof, and therefore does not contain an alkali metal component at all or even if it is contained, the semiconductor element is affected. It is preferable that the amount is as small as possible.
In addition, if bubbles are present in the glass substrate, it causes a display defect. Therefore, a glass substrate in which bubbles are present cannot be used as a glass substrate for FPD. For this reason, it is calculated | required that a bubble does not remain | survive in a glass substrate.

  In addition, when there is glass composition unevenness (non-uniform glass composition) on the glass substrate, for example, streak-like defects called striae are generated. This striae forms fine surface irregularities on the surface of the molten glass at the time of molding due to the difference in viscosity of the molten glass due to the inhomogeneity of the glass composition, and these surface irregularities remain on the glass substrate. For this reason, when this glass substrate is incorporated into a liquid crystal panel as a glass substrate for a liquid crystal panel, an error occurs in the cell gap or it causes display unevenness. For this reason, it is necessary not to cause unevenness of the glass composition such as striae in the manufacturing stage of the glass substrate.

For example, the hot spring of the molten glass is emphasized, the convection of the molten glass is promoted and the agitation is performed well, and the glass in the semi-molten state on the surface of the glass raw material input end side is prevented from prematurely flowing to the outlet end side. A glass melting furnace that can be used is known (Patent Document 1).
In the above glass melting kiln, a plurality of pairs of electrodes with the energizing direction as the length direction of the kiln are arranged at appropriate intervals in the hot spring region on the way from the glass material charging end region to the lead-out end region. The hot spring of the molten glass is emphasized by arranging the double rows over the entire length in the direction. Thereby, the glass in a semi-molten state or the like is prevented from flowing rapidly toward the lead-out end.

JP 2002-60226 A

However, SiO ₂ (silica) among the glass raw materials put into the glass melting kiln (melting tank) is more likely to remain unmelted than other raw material components. For this reason, when the hot spring is weak, SiO ₂ gathers on the liquid surface on the MTE (Melting End) side which is the lead-out end side of the molten glass of the glass melting furnace (melting tank) as shown in FIG. It is easy to form a silica-rich heterogeneous substrate 120. If the hot spring is always emphasized, the silica-rich heterogeneous base 120 will not flow quickly to the outlet end side, but in the case of a molten glass having a high viscosity glass composition, The glass temperature must be increased to reduce the viscosity. However, if the temperature of the molten glass is raised too high, ZrO ₂ (zirconia) contained to ensure corrosion resistance will elute into the molten glass from the inner side walls of the refractory etc. constituting the melting tank, and the glass will become devitrified. It may cause. For this reason, in the case of a molten glass having a highly viscous glass composition, it is difficult to increase the temperature of the molten glass to create convection.
Further, a glass substrate such as a flat display such as a liquid crystal display is required not to adversely affect characteristics of a semiconductor element such as a TFT (Thin Film Transistor) formed on the glass substrate. For this reason, it is preferable to use a non-alkali glass containing no alkali metal component as described above, or a glass containing a trace amount of alkali even if it contains an alkali metal component, as described above. However, since alkali-free glass and alkali-containing glass have high temperature viscosity, it is difficult to emphasize the hot spring as described above. That is, when manufacturing a glass substrate having a glass composition with high high-temperature viscosity, it is difficult to manufacture a glass substrate that suppresses unevenness of the glass composition such as striae using the above-described known method with emphasis on hot springs.

  Therefore, an object of the present invention is to provide a method for producing a glass substrate that can suppress unevenness of the glass composition such as striae by using a completely different method.

One embodiment of the present invention is a method for producing a glass substrate including a melting step in which a glass raw material is heated and melted in a melting tank.
Among the inner side walls of the melting tank in contact with the molten glass made in the melting tank, the bottom of the inner side wall facing the first direction is provided with an outlet for flowing the molten glass from the outlet toward the subsequent process,
Of the inner side walls of the melting tank that are in contact with the molten glass made in the melting tank, the inner side walls facing each other of the melting tank extend from the outer side of the melting tank to the surface of the inner side wall. At least three pairs are provided along the first direction,
In the melting process,
The glass raw material, by injecting the substantially entire surface of the liquid surface of the molten glass stored in the melting tank, making the glass melt temperature of the surface layer is uniform including a liquid surface,
Flowing the molten glass from the outlet;
When flowing the molten glass , electric power is applied between the pair of electrodes in the lower layer of the molten glass positioned below the surface layer in the depth direction of the molten glass, and the molten glass positioned in the lower layer is energized and heated. And the amount of heat given to the molten glass by the pair of electrodes on both sides in the first direction is generated inside the pair of electrodes on both sides so that convection due to the temperature distribution of the molten glass does not occur. While making the temperature distribution along the first direction of the lower layer molten glass uniform by increasing the amount of heat given to the molten glass by the pair of electrodes positioned, the molten glass is removed from the outlet through the post-process. Shed.

  In the manufacturing method of the glass substrate of the said form, the nonuniformity of glass compositions, such as striae, can be suppressed.

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 melting process-cutting process shown in FIG. It is a figure explaining the melting tank used at the melting process shown in FIG. It is a figure explaining injection | throwing-in of the glass raw material in the melting tank shown in FIG. It is a figure explaining the convection of the molten glass inside the melting tank in this embodiment. It is a figure explaining the convection of the molten glass inside the conventional melting tank.

  Hereinafter, the manufacturing method of the glass substrate of this embodiment is demonstrated. FIG. 1 is a diagram showing an example of steps of a method for producing a glass substrate according to the present invention.

(Overall overview of glass substrate manufacturing method)
The glass substrate manufacturing method includes a melting step (ST1), a clarification step (ST2), a homogenization step (ST3), a supply step (ST4), a forming step (ST5), and a slow cooling step (ST6). And a cutting step (ST7). In addition, a plurality of glass substrates that have a grinding process, a polishing process, a cleaning process, an inspection process, a packing process, and the like and are stacked in the packing process are transported to a supplier.

The melting step (ST1) is performed in a melting tank. In the melting tank, the glass raw material is introduced into substantially the entire liquid surface of the molten glass stored in the melting tank, thereby producing a molten glass having a uniform surface temperature including the liquid surface. Furthermore, molten glass is poured from the outflow port provided in the bottom part of the inner side wall which faces a 1st direction among the inner side walls of a melting tank toward a post process. At this time, the temperature of the lower layer of the molten glass positioned below the surface layer in the depth direction of the molten glass is adjusted so that the convection due to the temperature distribution of the molten glass does not occur in the lower layer. By adjusting at least the amount of heat applied to the molten glass positioned in the section, the molten glass is allowed to flow from the outlet to the subsequent process while uniforming the temperature distribution along the first direction of the underlying molten glass. For example, among the above temperature distributions, the temperature of the molten glass located at both ends in the first direction of the melting tank is likely to decrease, so the temperature is adjusted to increase this temperature and the temperature distribution in the lower layer is made uniform. . Moreover, when the temperature of the molten glass located in the said both ends tends to rise, temperature control is performed so that this temperature may be lowered, and the temperature distribution in the lower layer is made uniform.
Here, “substantially the entire surface” of the liquid surface of the molten glass into which the glass raw material is charged means 80% or more of the liquid surface of the molten glass in the melting tank. The glass raw material can be charged either by reversing the bucket containing the glass raw material and dispersing the glass raw material into the molten glass, by conveying the glass raw material by using a belt conveyor, or by dispersing the glass raw material. A method of sometimes charging, a method of dispersing glass raw material with a screw feeder, or a method of charging a substantially entire surface at a time may be used. In an embodiment described later, a glass raw material is charged using a bucket. The “surface layer” of the molten glass means a region including the liquid surface within a range of 5% or less of the depth from the liquid surface toward the bottom of the melting tank, and the “lower layer” of the molten glass is other than the surface layer. Refers to the area. In addition, the “bottom part” where the outflow port is provided is a part of the lower layer that is close to the bottom surface. Preferably, it refers to a region where the depth from the bottom surface in the depth direction of the dissolution tank is ½ or less of the depth between the liquid surface and the bottom of the dissolution tank.
The molten glass in the melting tank rises in temperature when electricity flows through the molten glass itself and generates heat. However, in addition to the heating of the molten glass by this energization, the heating glass is supplemented with a flame by a burner. The raw material can also be melted. A clarifier is added to the glass raw material. 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.

The clarification step (ST2) is performed at least in the clarification tank. In the clarification process, when the molten glass in the clarification tank is heated, bubbles containing O ₂ , CO ₂ or SO ₂ contained in the molten glass absorb O ₂ generated by the reductive reaction of the clarifier. As a result, the bubbles rise to the liquid surface of the molten glass and are discharged. 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 (ST3), the glass components are 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 stirring tanks may be provided.
In the supply step (ST4), the molten glass is supplied to the molding apparatus through a pipe extending from the stirring tank.

In the molding apparatus, a molding step (ST5) and a slow cooling step (ST6) are performed.
In the forming step (ST5), the molten glass is formed into a sheet glass to make a flow of the sheet glass. For forming, an overflow down draw method or a float method can be used. In this embodiment to be described later, an over download method is used.
In the slow cooling step (ST6), the sheet glass that has been formed and flowed is cooled to a desired thickness, so that internal distortion does not occur and warpage does not occur.
In a cutting process (ST7), a plate-shaped glass plate is obtained by cutting the sheet glass supplied from the forming device into a predetermined length in the cutting device. 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.

FIG. 2 is a diagram schematically illustrating an example of an apparatus that performs the melting step (ST1) to the cutting step (ST7) 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, and glass supply pipes 104, 105, and 106.
In the melting apparatus 101 of the example shown in FIG. 2, the glass raw material is charged using a bucket 101d. 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. In the forming apparatus 200, the sheet glass SG is formed from the molten glass MG by the overflow down draw method using the formed body 210.

(Detailed explanation of melting tank)
FIG. 3 is a diagram illustrating a schematic configuration of the melting tank 101 of the present embodiment.
The melting tank 101 makes molten glass in which the temperature of the surface layer including the liquid surface is made uniform by introducing the glass raw material to substantially the entire liquid surface 101 c of the molten glass MG stored in the melting tank 101. Further, among the inner side walls of the melting tank 101, the melting tank 101 is from an outlet 104 a provided at the bottom of the inner side wall in the left-right direction (first direction) in FIG. 3, more specifically leftward. The molten glass MG is poured toward the subsequent process.

  The melting tank 101 has a wall 110 made of a refractory material such as a refractory brick. The melting tank 101 has an internal space surrounded by a wall 110. The internal space of the melting tank 101 is formed in a liquid tank 101a that accommodates the molten glass MG formed by melting the glass raw material introduced into the space while being heated, and an upper layer of the molten glass MG. And an upper space 101b which is a gas phase.

  A wall 110 parallel to the first direction of the upper space 101b of the dissolution tank 101 is provided with a burner 112 that emits a flame by burning combustion gas mixed with fuel and oxygen. The burner 112 heats the refractory in the upper space 101b with a flame to raise the temperature of the wall 110. The glass raw material is heated by the radiant heat of the wall 110 that has become high temperature, or by the gas phase atmosphere that has become high temperature.

  In the left side wall of the melting tank 101 in FIG. 3, a raw material charging window 101f is provided on the surface in contact with the upper space 101b. Through this raw material charging window 101f, the bucket 101d containing the glass raw material enters and leaves the upper space 101b, and moves forward, backward, left and right on the liquid surface 101c of the molten glass MG in accordance with instructions from a computer 118 described later.

FIG. 4 is a view for explaining the introduction of the glass raw material in the melting tank 101.
As shown in FIG. 4, the glass raw material is charged over substantially the entire liquid surface of the molten glass MG stored in the melting tank 101. Thereby, molten glass MG in which the temperature of the surface layer including the liquid surface is made uniform is produced.
That is, the melting tank 101 is provided with a packet operation mechanism that moves the bucket 101d to a target area and reverses the upper surface of the bucket 101d to the lower surface in a state where the bucket 101d contains the glass raw material according to an instruction from the computer 118. The area where the glass material is charged by the bucket 101d and the time interval for the glass material are set in advance so that the glass material floating on the liquid surface 101c of the molten glass MG does not disappear. Therefore, in the melting tank 101, since it is thrown into substantially the whole liquid level of the molten glass MG, it always floats so that the glass surface covers the liquid level 101c of the molten glass MG.

The glass raw material is always floated so as to cover the liquid surface 101c because the heat of the molten glass MG does not radiate through the liquid surface 101c to the upper space 101b which is a gas phase, and the liquid surface of the molten glass MG This is because the temperature distribution of the surface layer including it is made uniform and kept constant. In addition, among glass raw materials, raw material components having low meltability (high melting temperature) such as SiO ₂ (silica) are efficiently melted to prevent unmelted raw material components such as SiO ₂ (silica). . High raw material components of melting temperature of SiO ₂ or the like, other components such as _B 2 _{O 3} in a state mixed with the raw material components such as (boron oxide), SiO ₂ at a temperature lower than the intrinsic melting temperature, such as SiO _2, Etc. can be dissolved. For this reason, the glass raw material is continuously dispersed and introduced so that the glass raw material always exists on the liquid surface 101c of the molten glass MG and covers the liquid surface 101c. _Accordingly, B 2 _{O 3} raw material components or the like, since the melted with the raw material components such as melted hard SiO _2, it is possible to prevent the remaining melted raw material components such as SiO ₂ (silica). As in the past, when glass raw material is thrown into a part of the liquid surface of the molten glass, raw material components such as SiO _{2 that} are difficult to melt remain undissolved, and the glass raw material is moved away from the glass raw material feeding position by convection of the molten glass. May float on the surface of the liquid as a foreign material. In addition, this heterogeneous substrate moves to the inside of the melting tank by convection of the molten glass, and in some cases, it flows out from the outlet of the melting tank and flows into the post-treatment process. Prone to cause.
For this reason, in this embodiment, in the melting tank 101, a glass raw material is thrown into the substantially whole surface of the liquid surface of molten glass MG. Therefore, the temperature in the surface layer including the liquid level of the molten glass MG is made uniform. It is also possible to prevent the remaining melted raw material components such as SiO _2.

Three pairs of electrodes 114 made of a heat-resistant conductive material such as tin oxide or molybdenum are provided on the inner side walls 110a and 110b of the liquid tank 101a parallel to the first direction of the melting tank 101 and facing each other. Is provided. The three pairs of electrodes 114 are provided in regions corresponding to the lower layer of the molten glass MG in the inner side walls 110a and 110b. All of the three pairs of electrodes 114 extend from the outer wall surface of the liquid tank 101a to the inner wall surface. Of each of the three pairs of electrodes 114, the electrode on the far side in the figure is not shown. Each pair of the three pairs of electrodes 114 is provided on the inner side walls 110a and 110b so as to face each other through the molten glass MG. Each pair of electrodes 114 passes a current through molten glass MG located between the electrodes. By this energization, the molten glass MG generates Joule heat by itself to heat the molten glass MG. In the melting tank 101, the molten glass MG is heated to, for example, 1500 ° C. or higher. The heated molten glass MG is sent to the clarification tank 102 through the glass supply pipe 104. Note that the distance in the first direction between the pair of electrodes 114 out of the three pairs of electrodes 114 and the pair of electrodes 114 adjacent to the pair is the same. This is preferable in that the temperature is controlled to make the temperature of the MG uniform.
In the present embodiment, the melting tank 101 is provided with three pairs of electrodes 114, but two pairs or four or more pairs of electrodes may be provided. Even in the case where there are four or more pairs of electrodes 114, the separation distance in the first direction between each pair of electrodes 114 and the pair of electrodes 114 adjacent to this pair is the same in the lower layer. This is preferable in that the temperature is controlled in order to make the temperature of the molten glass MG uniform.

  In the melting tank 101 shown in FIG. 3, the burner 112 is provided in the upper space 101b, but the burner 112 may not be provided. In a molten glass having a large specific resistance (for example, a molten glass having a specific resistance at 1500 ° C. of 180 Ω · cm or more), the burner 112 may be used as an auxiliary. The glass raw material is dispersed and introduced into the liquid surface 101c of the large area of the molten glass MG, and the heat radiation from the liquid surface 101c of the molten glass MG is prevented by covering substantially the entire surface of the liquid surface 101c with the glass raw material. A decrease in temperature can be suppressed. Thereby, the glass raw material can be melted by the temperature of the molten glass MG without using the burner 112 when continuously forming the molten glass.

  Each of the electrodes 114 is connected to the control unit 116, and the electric power (alternating current) supplied to each of the electrodes 114 is controlled for each pair of the electrodes 114 in order to make the temperature distribution of the molten glass MG in the lower layer uniform. Has been. The control unit 116 is further connected to a computer 118. The computer 118 receives from the control unit 116 the power that the control unit 116 applies to the electrodes 114, specifically the voltage and current values, and is sandwiched between the electrodes 114 in the melting tank 101 based on the voltage and current information. The temperature information of the molten glass MG is obtained. The computer 118 further aligns the temperature of the molten glass MG measured by each pair of the three electrodes 114 within a predetermined allowable range, for example, within 5 ° C., preferably within 3 ° C., based on this temperature information. As described above, an instruction of power to be applied to the electrode 114 is sent to the control unit 116. Further, the computer 118 instructs a bucket operation mechanism (not shown) to operate a bucket 101d described later through the control unit 116.

For example, the computer 118 obtains temperature information of the molten glass MG at a position sandwiched between the pair of electrodes 114 by the following method. That is, the voltage of each pair of electrodes 114 is E (V), the current is I (A), the cross-sectional area of the current flowing through the molten glass MG between the pair of electrodes 114 is S (m ² ), and the electrodes 114 The specific resistance ρ (Ω · m) of the molten glass MG is obtained according to the equation ρ = E / I × S / L where the length between the pair of L is m (m). The cross-sectional area S and the length L are values determined by the melting tank 101.
Since the specific resistance ρ varies depending on the temperature of the molten glass MG through which an electric current flows, the relationship between the specific resistance ρ and the temperature of the molten glass MG is obtained in advance, and is calculated by the computer 118 using this relationship. The temperature information of the molten glass MG can be obtained from the specific resistance ρ. The relationship between the specific resistance ρ and the temperature of the molten glass MG can be expressed by a functional expression of the specific resistance ρ, for example, F (ρ). For example, the function formula F (ρ) can be defined by the following formula. In general, the molten glass MG located in the vicinity of the inner side walls 110c and 110d facing the first direction is likely to become low temperature by heat radiation from the inner side walls 110c and 110d. For this reason, in this embodiment, the temperature distribution in the lower layer is made uniform by increasing the temperature at both ends of the melting tank 202 in the first direction.

Temperature T (° C.) of molten glass MG = a / (log (ρ) + b) −273.15
a, b: Constants depending on the glass composition.

  The outlet 104 a of the melting tank 101 is connected to the clarification tank 102 through the glass supply pipe 104.

FIG. 5 is a diagram for explaining convection of the molten glass inside the melting tank 101 in the present embodiment. In the present embodiment, the glass raw material is charged to substantially the entire liquid surface of the molten glass MG stored in the melting tank 101, thereby producing a molten glass MG having a uniform surface temperature including the liquid surface 101c. When this molten glass MG is flowed from the outlet 104a toward the subsequent step, the temperature of the lower layer of the molten glass MG in the depth direction of the molten glass MG is prevented so that convection due to the temperature distribution of the molten glass MG does not occur in the lower layer. In addition, among the temperature distribution along the horizontal direction (first direction) in FIG. 3 of the molten glass MG of the lower layer, the amount of heat given to the molten glass located at both ends in the horizontal direction in FIG. By adjusting at least, the temperature distribution in the lower layer is made uniform. It is from the left and right side walls in FIG. 3 that at least the amount of heat applied to the molten glass located at both ends so as to increase the temperature of the molten glass located at both ends in the left-right direction in FIG. This is because heat is easily released to the outside, and the temperature of the molten glass MG at the both ends is likely to be lower than that at the center. That is, the amount of heat applied to the molten glass positioned at both ends is adjusted so that the temperature of the molten glass positioned at both ends where the temperature tends to decrease increases. For this reason, the power supplied to the three pairs of electrodes 114 is higher for the electrodes 114 located on both sides than the center electrode 114 of the melting tank 101 in the left-right direction (first direction) in FIG. It is preferable to set. Therefore, the molten glass MG is pulled by the outflow from the outlet 104a of the molten glass MG and flows as shown by the arrows in FIG. 5 without causing convection due to the temperature distribution of the molten glass MG in the lower layer.
On the other hand, FIG. 6 is a figure explaining the convection of the molten glass inside the conventional melting tank. As shown in FIG. 6, in the conventional melting tank, in the region A, the molten glass is partially heated so that a pot spring is formed, and convection is promoted. For this reason, among the glass raw materials introduced into a part of the liquid surface of the molten glass, raw material components such as SiO _{2 that} are not easily melted move by convection, and for example, the silica-rich heterogeneous substrate 120 is separated from the glass raw material introduction position. It is easy to collect in. In addition, the opportunity for this heterogeneous substrate 120 to flow out of the outlet along the convection increases, which tends to cause unevenness in the glass composition such as striae.

Thus, in this embodiment, the molten glass in which the temperature of the surface layer including the liquid surface 101 c is made uniform by introducing the glass raw material to substantially the entire liquid surface of the molten glass MG stored in the melting tank 101. create. Furthermore, molten glass MG is poured from the outflow port 104a provided in the bottom part of the inner side wall facing the first direction among the inner side walls of the melting tank 101 toward the subsequent step. At this time, at least the amount of heat given to the molten glass MG positioned at both ends in the first direction of the melting tank so that the convection due to the temperature distribution of the molten glass does not occur in the lower layer. By adjusting the temperature, the molten glass MG is allowed to flow from the outlet to the subsequent process while making the temperature distribution along the first direction of the lower layer molten glass MG uniform. For example, among the temperature distribution along the first direction of the lower layer molten glass MG, by increasing the temperature of the molten glass MG, the temperature located at both ends of the melting tank 101 in the first direction is likely to decrease, While making the temperature distribution in the lower layer uniform, the molten glass MG is caused to flow from the outlet 104a to the clarification step. For this reason, since convection due to the temperature distribution of the molten glass MG does not occur in the lower layer, it is possible to suppress unevenness of the glass composition due to the heterogeneous substrate 120 or the like. In addition, when the temperature distribution of the molten glass MG is not uniform in the lower layer, a temperature difference distribution is generated between the lower layer and the surface layer where the temperature is uniformed, so that conventional hot spring convection is easily performed.
Accordingly, the temperature of molten glass having high viscosity, for example, 10 ^2.5 poise of molten glass is 1300 ° C. or higher (eg, 1300 ° C. or higher and 1650 ° C. or lower), more preferably 1500 ° C. or higher (eg, 1500 ° C. or higher and 1650 ° C.). The manufacturing method of the present embodiment can be applied even in the case of molten glass that is the following), and there is an advantage that unevenness of the glass composition such as striae can be suppressed as compared with the conventional manufacturing method. large. In addition, even in molten glass with a high specific resistance of 1500 Ω · cm or higher at 1500 ° C., it is not necessary to apply an excessive voltage to emphasize the hot spring, so that current does not flow through the refractory. Can do. For this reason, since ZrO ₂ (zirconia) that tends to cause devitrification of the glass can be prevented from eluting from the inner side wall in contact with the molten glass MG of the melting tank 101, unevenness of the glass composition can be suppressed. The manufacturing method of the embodiment is suitable. Moreover, you may use together the heating by a burner in the melting tank 101 about such molten glass with a large specific resistance.

In the present embodiment, each pair of the three pairs of electrodes 114 faces each other in the direction orthogonal to the right and left direction (first direction) in FIG. 3, and therefore the first of the molten glass MG. The temperature in the lower layer along the direction can be effectively made uniform.
Moreover, in this embodiment, the electric power supplied to the three pairs of electrodes 114 is more at the both end portions than in the central portion of the melting tank 101 in the first direction in consideration of heat release from the melting tank 101. Since it supplies so that it may become high, it is easy to equalize the temperature distribution in the 1st direction of the molten glass MG in a lower layer.

In the present embodiment, since the temperature in the lower layer of the molten glass MG is made uniform so as not to draw the convection due to the temperature distribution of the molten glass, the convection due to the temperature distribution of the molten glass is promoted as in the prior art. Therefore, it is not necessary to partially heat the molten glass to an excessively high temperature at the expense of elution of the refractory constituting the melting tank 101. For this reason, ZrO ₂ (zirconia), which is likely to cause devitrification of the glass, is difficult to elute from the inner side wall in contact with the molten glass MG of the melting tank 101 and corrodes. Therefore, the melting method of this embodiment is suitable when the inner side wall of the melting tank 101 is constituted by a refractory containing ZrO ₂ having excellent corrosion resistance as a component.

(Glass composition)
The composition of the glass used in the present embodiment is composed of aluminosilicate glass, SiO 2 and _(silica) may comprise more than 50 wt%. The manufacturing method of this embodiment applied to an aluminosilicate glass having this glass composition can effectively suppress unevenness of the glass composition as compared with the conventional method. Furthermore, SiO ₂ can be contained in an amount of 55% by mass or more, and SiO ₂ can be contained in an amount of 60% by mass or more. The manufacturing method of this embodiment to which the aluminosilicate glass having these compositions is applied can more effectively suppress glass composition unevenness than the conventional method. Even if the glass composition contains 50% by mass or more of SiO ₂ and easily forms a silica-rich heterogeneous substrate, the molten glass MG is melted so that convection due to the temperature distribution does not occur. Outflow from the outlet 104a can be prevented. In addition, since the glass raw material is always added to the liquid surface 101c so as to have a certain thickness, SiO ₂ is prevented from remaining melted, and the heterogeneous substrate 120 due to SiO ₂ as shown in FIG. Further, when a glass composition containing 50% by mass or more of SiO ₂ and having a high viscosity of the molten glass MG is used for the glass substrate, and convection of the molten glass is promoted as in the conventional case, ZrO ₂ contained in the refractory constituting the melting tank. (Zirconia) may elute into the molten glass and cause devitrification of the glass. However, since this embodiment makes the temperature distribution of the molten glass MG in the lower layer uniform so as not to cause convection due to the temperature distribution of the molten glass MG, it is necessary to heat the molten glass to an excessively high temperature as in the prior art. There is no. For this reason, elution of ZrO ₂ (zirconia) from the refractory in the dissolution tank 101 can be prevented. The upper limit of the content in the glass composition of SiO ₂ is 70 wt% for example.

Can also include a SiO ₂ and Al ₂ O ₃ in a total of 60 mass% or more, the manufacturing method of the present embodiment applying the aluminosilicate glass having the glass composition is effectively glass composition as compared with the conventional Can be suppressed. Furthermore, SiO ₂ and Al ₂ O ₃ can be contained in a total of 65% by mass or more, and SiO ₂ and Al ₂ O ₃ can be contained in a total of 70% by mass or more. Even if the glass composition contains SiO ₂ and Al ₂ O ₃ in a total of 60% by mass or more and easily forms a silica-rich heterogeneous substrate 120, the molten glass MG is melted so that convection due to the temperature distribution does not occur. Therefore, the silica-rich heterogeneous substrate can be prevented from flowing out from the outlet 104a. In addition, since the glass raw material is always added to the liquid surface 101c so as to have a certain thickness, SiO ₂ is prevented from remaining melted, and the heterogeneous substrate 120 due to SiO ₂ as shown in FIG. In addition, when a glass composition containing 60% by mass or more of SiO ₂ and Al ₂ O ₃ in total and having a high viscosity of molten glass MG is used for the glass substrate, and convection of the molten glass is promoted as in the past, a melting tank is configured. ZrO ₂ (zirconia) contained in the refractory to be eluted into the molten glass may cause devitrification of the glass. However, in the present embodiment, the temperature distribution of the molten glass MG in the lower layer is made uniform so as not to cause convection due to the temperature distribution of the molten glass MG. There is no need to heat. For this reason, elution of ZrO ₂ (zirconia) from the refractory in the dissolution tank 101 can be prevented. In the glass composition, the upper limit of the total content of SiO ₂ and Al ₂ O ₃ is, for example, 95% by mass.
The glass substrate is preferably composed of aluminoborosilicate glass. B ₂ O ₃ (boron oxide) were melted at a low temperature as compared with SiO _2, moreover, to lower the melting temperature of the SiO _2. Therefore, in a glass composition having a high SiO ₂ content, the inclusion of B ₂ O ₃ is effective in that the heterogeneous substrate 120 (see FIG. 6) is hardly generated.

The glass composition of a glass substrate can mention the following, for example.
The content rate display of the composition shown below is mass%.
SiO _2: 50~70%,
B ₂ O _3: 5~18%,
Al ₂ O _3: 0~25%,
MgO: 0 to 10%,
CaO: 0 to 20%,
SrO: 0 to 20%,
BaO: 0 to 10%,
RO: 5 to 20% (However, R is at least one selected from Mg, Ca, Sr and Ba, and the glass substrate contains),
It is preferable that it is an alkali free glass containing.

Moreover, about the glass of a glass substrate, the following glass compositions can be mentioned.
SiO _2: 50~70%,
B ₂ O ₃ : 1 to 10%,
Al ₂ O _3: 0~25%,
MgO: 0 to 10%,
CaO: 0 to 20%,
SrO: 0 to 20%,
BaO: 0 to 10%,
RO: 5 to 30% (where R is the total amount of Mg, Ca, Sr and Ba),
Similarly, it is also preferable that the glass be an alkali-free glass.

Moreover, about the glass of a glass substrate, the following glass compositions can be mentioned.
SiO _2: 50~70%,
B ₂ O ₃ : _{3 to} 15%,
Al ₂ O _3: 8~25%,
MgO: 0 to 10%,
CaO: 0 to 20%,
SrO: 0 to 20%,
BaO: 0 to 10%,
RO: 5 to 20% (where R is the total amount of Mg, Ca, Sr and Ba),
Similarly, it is also preferable that the glass be an alkali-free glass.

Although the alkali-free glass is used in the present embodiment, the glass substrate may be a glass containing a trace amount of alkali metal (the total content of alkali gold images is greater than 0% by mass). When an alkali metal is contained, the total of R ′ ₂ O is 0.10% or more and 0.5% or less, preferably 0.20% or more and 0.5% or less (where R ′ is selected from Li, Na, and K) It is preferable that the glass substrate contains at least one kind. Moreover, in order to make glass melting easy, it is more preferable that content of the iron oxide in glass is 0.01 to 0.2% from a viewpoint of reducing a specific resistance. _Further, it is preferred not to include _{As 2 O 3, Sb 2 O} 3 and PbO substantially.

The manufacturing method of this embodiment can be effectively applied to the glass substrate for liquid crystal display devices. As described above, the glass substrate for a liquid crystal display device suppresses the thermal expansion of the glass substrate and does not deteriorate the characteristics of the TFT (Thin Film Transistor) formed on the glass substrate. (Li, Na, and K) are not included, or even if included, a trace amount is preferable. However, when alkali metal components (Li, Na and K) are not contained or are contained in a very small amount, the high temperature viscosity of the molten glass MG is increased. Need to be partially heated to high temperatures. In the present embodiment, the glass raw material is charged over substantially the entire liquid surface 101c of the molten glass MG, and the temperature of the molten glass MG is adjusted so that convection of the molten glass MG does not occur. In order to make the temperature distribution of the molten glass, it is not necessary to partially heat the molten glass MG to a high temperature. Therefore, the manufacturing method of this embodiment can be suitably applied to a glass substrate for a liquid crystal display device in that the temperature of the molten glass is not partially excessively increased as in the prior art.
In addition, it is preferable that SnO ₂ (tin oxide) is contained in an amount of 0.01 to 0.5% by mass as a clarifier because the environmental load is reduced and an efficient clarification effect is exhibited.

In the present embodiment, SnO ₂ is used as a clarifier from the viewpoint of reducing the environmental load. However, in order to effectively function the clarification action of SnO ₂ , it is preferable that the melting temperature is not set too high. In the present embodiment, the temperature of the molten glass MG is not required to partially heat the molten glass in order to emphasize the hot spring as in the conventional known manufacturing method. In addition to preventing elution of ZrO ₂ (zirconia), the clarification action of SnO ₂ can be effectively functioned.

  Moreover, in this embodiment, in order to equalize the temperature in the lower layer of the molten glass MG more effectively in the melting tank 101, a heat retaining member is provided around the portion where the electrode 114 is provided on the outer side wall of the melting tank 101. Is preferably provided. As the heat insulating material, for example, a plate member obtained by hardening a heat insulating material such as glass wool or ceramic fiber into a plate shape or the like is used. Thereby, the heat radiation from the outer side wall of the melting tank 101 can be prevented, the temperature of the molten glass MG can be made more uniform in the melting tank 101, and the convection of the molten glass MG can be further reduced.

  As mentioned above, although the manufacturing method of the glass substrate of this invention was demonstrated in detail, this invention is not limited to the said embodiment, In the range which does not deviate from the main point of this invention, you may make various improvement and a change. Of course.

DESCRIPTION OF SYMBOLS 100 Melting apparatus 101 Melting tank 101a Liquid tank 101b Upper space 101c Liquid surface 101d Bucket 101f Raw material input window 102 Clarification tank 103 Stirring tank 103a Stirrer 104, 105, 106 Glass supply pipe 110 Wall 110a, 110b, 110c, 110d Inner side wall 112 Burner 114 Electrode 116 Control unit 118 Computer 120 Heterogeneous substrate 200 Molding device 210 Molded body 300 Cutting device

Claims (10)

Including a melting step of heating and melting glass raw material in a melting tank,
Among the inner side walls of the melting tank in contact with the molten glass made in the melting tank, the bottom of the inner side wall facing the first direction is provided with an outlet for flowing the molten glass from the outlet toward the subsequent process,
Of the inner side walls of the melting tank that are in contact with the molten glass made in the melting tank, the inner side walls facing each other of the melting tank extend from the outer side of the melting tank to the surface of the inner side wall. At least three pairs are provided along the first direction,
In the melting process,
The glass raw material, by injecting the substantially entire surface of the liquid surface of the molten glass stored in the melting tank, making the glass melt temperature of the surface layer is uniform including a liquid surface,
Flowing the molten glass from the outlet;
When flowing the molten glass , electric power is applied between the pair of electrodes in the lower layer of the molten glass positioned below the surface layer in the depth direction of the molten glass, and the molten glass positioned in the lower layer is energized and heated. And the amount of heat given to the molten glass by the pair of electrodes on both sides in the first direction is generated inside the pair of electrodes on both sides so that convection due to the temperature distribution of the molten glass does not occur. While making the temperature distribution along the first direction of the lower layer molten glass uniform by increasing the amount of heat given to the molten glass by the pair of electrodes positioned, the molten glass is removed from the outlet through the post-process. A method for producing a glass substrate, comprising: The electric power supplied to the pair of electrodes is located on both sides of the melting tank in the first direction as compared to the electrode located in the center part of the first direction of the melting tank in the first direction. The manufacturing method of the glass substrate of Claim 1 with a higher electrode. The inner side wall which contact | connects the said molten glass of the said melting tank is a manufacturing method of the glass substrate of Claim 1 or 2 comprised by the refractory material which contains a zirconia in a component. The temperature at 10 ^2.5 poise of molten glass is 1300 ° C. or higher, a glass substrate manufacturing method according to any one of claims 1-3. Glass substrate prepared above is composed of aluminosilicate glass, including SiO ₂ more than 50 wt%, a glass substrate manufacturing method according to any one of claims 1-4. The glass substrate produced is composed of aluminosilicate glass, and SiO ₂ and Al ₂ O ₃ in total including 60% by mass or more, a manufacturing method of a glass substrate according to claim 5.   The said glass substrate manufactured is a manufacturing method of the glass substrate of any one of Claims 1-7 comprised with an alkali free glass or alkali trace content glass. The specific resistance at 1500 ° C. of the molten glass is 180 ohms · cm or more, a manufacturing method of a glass substrate according to any one of claims 1-7. Wherein the glass raw material, tin oxide is added as a refining agent, method for producing a glass substrate according to any one of claims 1-8. The manufacturing method of the glass substrate of Claim 1 with which a heat retention member is provided in the outer side wall of the said melting tank around the part in which the said electrode pair is provided.

Images