KR101538242B1 - Method of making glass sheet - Google Patents

Abstract

A method for producing a glass plate includes a dissolving step of dissolving a glass raw material containing SnO ₂ as a refining agent at least by conduction heating to form a molten glass and a step of heating the molten glass at a heating rate of 2 ° C / Deg.] To 1630 [deg.] C or higher to generate bubbles in the molten glass to perform defoaming, and a process of absorbing bubbles in the molten glass into the molten glass by lowering the molten glass after the defoaming treatment And a shaping step of shaping the molten glass after the refining step into plate-like glass.

Description

[0001] METHOD OF MAKING GLASS SHEET [0002]

The present invention relates to a method of manufacturing a glass plate by a down-draw method.

A glass substrate having a thickness of 0.5 to 0.7 mm, for example, is used for a glass substrate used for a flat panel display (hereinafter referred to as "FPD") such as a liquid crystal display or a plasma display. This glass substrate for FPD, for example, has a size of 300 x 400 mm in the first generation, and a size of 2850 x 3050 mm in the tenth generation.

In order to produce a glass substrate for an FPD with a large size after the eighth generation, an overflow down draw method is most widely used. The overflow down-draw method includes a step of forming a plate-like glass from the lower side of the formed article by making the molten glass overflow from the upper side of the formed article in the molding furnace, and a step of slowly cooling the plate-shaped glass from the annealed furnace. In the gradual cooling furnace, the plate-like glass is drawn between the paired rollers and stretched to a desired thickness, and then the plate-like glass is slowly cooled so as to reduce internal deformation and heat shrinkage of the plate-like glass. Thereafter, the flaky glass is cut into a predetermined size and made into a glass plate, which is stacked on another glass plate and stored. Or the glass plate is conveyed to the next process.

The glass plate produced by such a molding is used for a glass substrate of a liquid crystal display in which semiconductor elements are formed on the glass surface. However, in order that the characteristics of the semiconductor elements formed on the glass surface are not deteriorated by the glass composition of the glass substrate, A glass plate containing no alkali metal component or containing a small amount of alkali metal is suitably used.

However, when bubbles are present in the glass plate, it causes display defects. Therefore, the glass plate in which bubbles exist is not suitable as a glass substrate for a flat panel display. Therefore, it is required that bubbles do not remain on the glass plate. Particularly, in a glass substrate for a liquid crystal display or a glass substrate for an organic EL display, the demand for bubbles is strict.

However, in order to suppress the deterioration of the characteristics of the semiconductor element, a glass plate which does not contain an alkali metal component or contains a small amount of an alkali metal component has a high-temperature viscosity higher than that of a glass plate containing a large amount of alkali metal such as soda lime glass There is a problem that bubbles are difficult to escape from the molten glass during production.

From the viewpoint of reducing the environmental load, it is required to limit the use of As ₂ O ₃ , which has been conventionally used, and which is highly toxic. Therefore, in recent years, the As ₂ O ₃ in place of As ₂ O ₃ on fining function is SnO ₂ or Fe ₂ O ₃ less than has been used as a refining agent. SnO ₂ or Fe ₂ O ₃ causes loss of transparency or coloration of the glass, and thus it can not be said that SnO ₂ or Fe ₂ O ₃ is added to glass in a large amount in order to secure a purifying function equivalent to As ₂ O ₃ . As a result, bubbles are more likely to remain on the glass plate as a final product.

On the other hand, in order to improve the defoaming effect in the production method of a glass substrate in which an alkali-free glass which is vitrified at 1300 to 1500 ° C is defoamed by raising the temperature to, for example, 1650 ° C, A value of 0.485 / mm or more has been proposed (Patent Document 1).

Japanese Patent Application Laid-Open No. 2005-97090

Here, for example, in the case of a glass composition which does not contain alkali metal or contains a small amount of alkali metal, solubility of SO ₂ that can be dissolved in the molten glass is small. Therefore, once bubbles of SO ₂ are generated, It is likely to remain as defects of the bubbles on the glass plate.

However, the technique described in Patent Document 1 has a problem that the generation of SO ₂ bubbles after the finishing process can not be sufficiently suppressed.

Therefore, it is an object of the present invention to provide a method of manufacturing a glass plate capable of effectively reducing bubbles remaining on a glass plate when producing the glass plate.

A first aspect of the present invention is a method for producing a glass plate.

In the above manufacturing method,

A dissolving step of dissolving a glass raw material containing SnO ₂ as a refining agent at least by conduction heating to form a molten glass;

Degassing treatment for producing bubbles in the molten glass by heating the molten glass to a temperature of 1630 DEG C or higher at a heating rate of 2 DEG C / min or more after the melting process, A bake process including an absorption process in which the bubbles in the molten glass are absorbed into the molten glass;

And a molding step of molding the molten glass after the refining step into a plate-shaped glass.

At this time, it is preferable that the produced glass sheet contains SnO ₂ in an amount of 0.01 to 0.5% by mass. The produced glass sheet preferably contains SnO ₂ and Fe ₂ O ₃ in combination. In this case, it is preferable that 0.01 to 0.5 mass% of SnO ₂ and 0.01 to 0.1 mass% of Fe ₂ O ₃ are contained desirable.

A second aspect of the present invention is the method for producing a glass plate according to the first aspect of the present invention, wherein the above-mentioned forming step forms a plate glass from the molten glass by an overflow down-draw method.

In a third aspect of the present invention, it is preferable that the temperature of the molten glass in the refining step be at least a value obtained by using at least a metal tube connecting between a melting vessel in which the melting step is performed and a blue sign in which the refining step is performed, Which is carried out by controlling the current to be passed through the glass plate.

A fourth aspect of the present invention is a method for producing a glass plate according to any one of the first to third aspects of the present invention, wherein the viscosity of the molten glass at a temperature of 1630 캜 is 130 to 350 poise.

In a fifth aspect of the present invention, there is provided the glass plate described above, wherein the content of R ' ₂ O is 0 to 2.0% by mass (R' ₂ O is the total of components including Li ₂ O, Na ₂ O and K ₂ O) The glass plate according to any one of the first to fourth aspects of the present invention.

In a sixth aspect of the present invention, there is provided the glass plate described above, wherein the glass plate comprises 50 to 70 mass% of SiO ₂ , 5 to 18 mass% of B ₂ O ₃ , 10 to 25 mass% of Al ₂ O ₃ , 0 to 10 mass% 0 to 20 mass% of CaO, 0 to 20 mass% of SrO, 0 to 10 mass% of BaO and 5 to 20 mass% of RO, wherein R is at least one kind selected from Mg, Ca, Sr and Ba And RO is a total of components including MgO, CaO, SrO, and BaO). The glass plate according to any one of the first to fifth aspects of the present invention is a process for producing a glass plate.

In a seventh aspect of the present invention, in the absorption treatment, the glass plate according to any one of the first to sixth aspects of the present invention, in which the molten glass is cooled to a temperature at a temperature of 2 DEG C / min or more in a range of 1600 to 1500 DEG C, .

An eighth aspect of the present invention is a method for producing a glass composition, comprising a stirring step for homogenously stirring a molten glass component between the refining step and the molding step,

In the dissolution step, the molten glass is supplied to the refining step at a temperature higher than the temperature at the start of dissolution of the molten glass,

In the refining step, the molten glass is supplied to the stirring step at a temperature lower than the temperature after the absorption treatment,

In the molding step, any one of the first to seventh aspects of the present invention, in which the molten glass is supplied at a temperature of log? = 4.3 to 5.7 with respect to the viscosity? (Poise) of the molten glass, Wherein the glass plate is a glass plate.

The method of manufacturing a glass plate in this embodiment can effectively reduce bubbles remaining on a glass plate.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a process chart of a manufacturing method of a glass plate of the present embodiment; Fig.
Fig. 2 is a diagram schematically showing an apparatus for performing a dissolving process or a cutting process in the manufacturing method of a glass plate according to the present embodiment. Fig.
Fig. 3 is a view mainly showing a configuration of the apparatus for performing the finishing process of the present embodiment. Fig.
4 is a view mainly showing a configuration of a device for carrying out a forming step and a cutting step according to the present embodiment.
5 is a view for explaining an example of the temperature history from the dissolving process to the forming process of the present embodiment.
6 is a graph showing the relationship between the amount of O ₂ released and the rate of temperature rise included in the molten glass when defoaming treatment of the present embodiment is performed.
7 is a view showing a result of measurement of the content of SO ₂ contained in holes in a glass in which bubbles remaining on a glass plate are reproduced.
8 is a graph showing the relationship between the bubble level and the rate of temperature decrease when a glass plate is manufactured in an experiment simulating the temperature history of the molten glass shown in Fig.
9 is a view showing the relationship between the bubble level and the rate of temperature decrease in the glass plate when the glass plate is manufactured by using the apparatus for producing the glass plate shown in Fig.
10 is a graph showing the relationship between the bubble level and the temperature raising rate in the glass plate when the glass plate is manufactured using the apparatus for producing the glass plate shown in Fig.

Hereinafter, a method of manufacturing the glass plate of the present embodiment will be described.

(Overview of Manufacturing Method of Glass Plate)

Fig. 1 is a process diagram of a manufacturing method of a glass plate according to the present embodiment.

The glass plate manufacturing method includes a melting step (ST1), a refining step (ST2), a homogenizing step (ST3), a supplying step (ST4), a molding step (ST5), a slow cooling step (ST6) (ST7). In addition, a plurality of glass plates stacked in the packing process, which have a grinding process, a polishing process, a cleaning process, an inspection process, a packing process, and the like, are returned to the supplier.

Fig. 2 is a diagram schematically showing a glass substrate manufacturing apparatus for performing the dissolving step (ST1) to cutting step (ST7). As shown in Fig. 2, the apparatus mainly has a dissolving apparatus 200, a molding apparatus 300, and a cutting apparatus 400. Fig. The dissolving apparatus 200 mainly has a melting tank 201, a blue sign 202, a stirring tank 203 and glass feed pipes 204, 205 and 206. Further, the glass supply pipes 204 and 205 are metal pipes for flowing the molten glass MG as described later, and also have a purifying function, so that they are also virtually blue signatures. Hereinafter, the glass supply pipe 204 is referred to as a first blue sign 204, the blue sign 202 is referred to as a second blue sign 202, and the glass feed pipe 205 is referred to as a third blue sign 205. After the melting bath 201, the first blue sign 204, the third blue sign 205, the glass feed pipe 206, and the second blue sign 204, which connect the respective tanks to the molding apparatus 300, The main body portion of the stirring tank 202 and the stirring tank 203 is made of platinum or a platinum alloy tube. The first blue circle 204 and the third blue circle 205 have a cylindrical shape or a trough shape.

In the dissolving step (ST1), SnO by ₂ is added as a refining agent dissolves in the glass raw material including a glass raw material, that SnO ₂ is supplied in a melting vessel 201, a refining agent, to the energization heating with at least the electrode, the molten Obtain a glass. In addition to conduction heating using an electrode, a molten glass may be obtained by dissolving a glass raw material by using a flame (not shown). Specifically, in the case of dissolving the glass raw material using the electric heating and the flame, the glass raw material is dispersed on the liquid surface of the molten glass MG by using a raw material feeding device (not shown). The glass raw material is heated by the gaseous phase at a high temperature by the flame and gradually dissolves and melts in the molten glass MG. The molten glass MG is heated by energization heating. Bubbling with oxygen gas may be performed in the molten glass between the melting step or the melting step and the finishing step. Bubbling is preferably not performed at the beginning of the dissolving step. This is because when the molten glass MG is energized and heated in the melting tank 201 at the beginning of the melting process (for example, the temperature of the molten glass is lower than 1540 占 폚), the electric power of the member such as the brick constituting the melting tank 201 This is because the electric resistance of the glass is larger than the resistance, so that electric current easily flows through members such as bricks, and it becomes difficult to heat the molten glass MG using the electrodes.

The fining step ST2 is performed in at least the first blue sign 204, the second blue sign 202 and the third yellow sign 205. In the refining step, the molten glass MG in the first blue oven 204 is heated, and thereby O ₂ , CO ₂ or SO ₂ Or the like absorbs O ₂ generated by the reduction reaction of SnO _{2 as} a clearing agent and grows, and is discharged on the liquid surface of the molten glass MG. Further, in the cleaning step, the internal pressure of the gas component in the bubbles is lowered due to the lowering of the temperature of the molten glass MG, and the SnO ₂ obtained by the reduction reaction of SnO ₂ performs the oxidation reaction by lowering the temperature of the molten glass MG, O ₂ in the bubbles remaining in the molten glass MG Are reabsorbed in the molten glass MG, and the bubbles disappear. The oxidation reaction and the reduction reaction by the cleaning agent are performed by adjusting the temperature of the molten glass MG. Adjustment of the temperature of the molten glass MG is performed by adjusting the temperatures of the first blue sign 204, the second blue sign 202 and the third yellow sign 205. The adjustment of the temperature of each blue sign may be performed by direct energization heating to flow electricity to the pipe itself or by placing the first blue sign 204, the second blue sign 202 and the third yellow sign 205 around Indirect heating by heating the respective tanks using a heater, indirect cooling by a cooler of air cooling and water cooling, and air blowing to the first blue sign 204, the second blue sign 202 and the third yellow sign 205 , Water spraying, or the like, or a combination of these methods. In FIG. 2, the group for purifying is divided into three parts, that is, the first blue circle 204, the second blue circle 202 and the third blue circle 205, but it goes without saying that they are further subdivided.

In the adjustment of the temperature of the molten glass MG of the present embodiment, direct energization heating, which is one of the methods described above, is used. Specifically, a metal flange (not shown) provided in the first blue bulb 204 for supplying the molten glass MG to the second blue bulb 202, a metal flange (not shown) provided in the second blue bulb 202, (Not shown) provided in the second blue oven 202 and a second blue oven (not shown) on the downstream side of the molten glass MG with respect to the metal flange The temperature of the molten glass MG is adjusted by flowing an electric current between the metal flange (not shown) provided on the molten glass (not shown) and the molten glass MG. In the present embodiment, a constant current is supplied to the first region between the metal flanges and the second region between the metal flanges, respectively, and the first blue bulb 204 and the second blue bulb 202 are energized and heated, However, this energization heating is not limited to the temperature adjustment by energization heating of two areas, but the energization heating is performed in one area or the energization heating is performed in three or more areas, Temperature adjustment may be performed.

In the homogenization step (ST3), the molten glass MG in the stirring tank 203 supplied through the third gradually rising glass (205) is agitated by using a stirrer (203a) to homogenize the glass components. Two or more stirring vessels 203 may be provided.

In the supplying step ST4, the molten glass is supplied to the molding apparatus 300 through the glass supply pipe 206. [

In the molding apparatus 300, a molding step (ST5) and a slow cooling step (ST6) are performed.

In the molding step (ST5), the molten glass is formed into the plate-like glass G, and the flow of the plate-like glass G is made. In the present embodiment, an overflow down draw method using a formed body 310 to be described later is used. In the gradual cooling step (ST6), the plate-like glass G that is formed and flows is cooled so that internal deformation does not occur.

 In the cutting step ST7, the plate glass G fed from the molding machine 300 is cut to a predetermined length by the cutting device 400 to obtain a glass plate. The cut glass plate is further cut to a predetermined size to produce a glass plate having a target size. Thereafter, the end surface of the glass is subjected to grinding, polishing and cleaning of the glass plate, and after the presence or absence of defects such as bubbles or striae is examined, the glass plate of the inspection-accepted product is packed as a final product.

(Cleaning process)

Fig. 3 is a view mainly showing a configuration of a device for performing a cleaning process. The refining process includes a defoaming process and an absorption process. In the degassing process, the temperature was raised to the molten glass MG with more than 1630 ℃, the refining agent SnO and ₂ give off oxygen, by pulling the oxygen in conventional air bubbles B of the molten glass MG, extends the traditional bubble diameter of the bubbles B . As a result, the increase in the bubble diameter due to the increase in the internal pressure of the gas component in the bubble B due to the temperature rise of the molten glass MG and the increase in the viscosity of the molten glass MG due to the temperature rise of the molten glass MG The rising speed of the air bubble B is increased, and the defoaming is promoted.

In the absorption treatment, contrary to defoaming treatment, the temperature of the molten glass MG is lowered so that the oxygen in the bubble B in the molten glass MG is absorbed again into the molten glass MG, and the temperature of the molten glass MG is lowered By reducing the internal pressure, the bubble diameter is reduced by the synergistic effect, and the bubble B is extinguished in the molten glass MG.

Further, in the defoaming step, the temperature of the molten glass MG is raised to 1630 DEG C or higher at a heating rate of 2 DEG C / min or more. The rate of temperature increase of 2 deg. C / min or more is set so that the temperature of the molten glass MG changes from the temperature of the molten glass MG after the melting process (for example, 1580 deg. C and 1560 deg. C to 1620 deg. 1700 占 폚), the average heating rate of the molten glass MG is 2 占 폚 / min or more. For example, in the case where the temperature of the molten glass MG in the first blue sign 204 is 1630 DEG C or higher, the rate of temperature rise is set such that the temperature of the molten glass MG in the first blue sign 204 connected from the outlet of the melting tank 200 The average rate of temperature rise from inlet to outlet.

The first blue sign 204, the second blue sign 202 and the third blue sign 205 give the above-mentioned temperature history to the molten glass MG, whereby the molten glass MG is defoamed and the bubble B is absorbed . Accordingly, it has a temperature regulation function that allows the first blue sign 204, the second blue sign 202 and the third blue sign 205 to be heated and cooled to a desired temperature.

The temperature adjustment of each of the first blue sign 204, the second blue sign 202 and the third blue sign 205 may be performed by direct energization heating for energizing each blue sign itself, (Not shown), indirect cooling of the blue sign by air cooling, indirect cooling by a cooler of water-cooling, air injection into each cleaning tank, water spraying, or a combination of these methods .

3, refinement will be described in more detail.

The molten glass MG in the liquid phase which is dissolved in the melting tank 201 and contains a large amount of the bubbles B generated by the decomposition reaction of the glass raw material is introduced into the first blue sign 204.

In the first blue circle 204, the molten glass MG is heated up to 1630 DEG C or higher by heating the platinum or platinum alloy tube, which is the body of the first blue circle 204, and the reducing reaction of the refining agent is promoted, Oxygen is released to the molten glass MG. Existing bubbles B in the molten glass MG are formed in such a manner that the oxygen released by the reduction reaction of the fining agent increases in the bubble diameter due to the synergistic effect of the pressure of the gas component in the bubble B, B, and the bubble diameter of the existing bubble B is enlarged by this synergistic effect. At this time, the fused glass MG is heated until the temperature reaches 1630 DEG C or more at a heating rate of 2 DEG C / min or more. Since the first blue sign 204 has a smaller tube cross section than the second blue sign 202 and the upper open space does not have a meteorous atmosphere space unlike the second blue sign 202, In the first blue circle 204, since the molten glass MG is filled and flows in the entire inside cross-section of the first blue circle 204, the temperature of the molten glass MG is efficiently increased as compared with the second blue circle 202 . That is to say, the temperature of the molten glass MG in the first blue oven 204 is raised to 1630 ° C. or more, rather than the temperature of the molten glass MG is raised to 1630 ° C. or more in the second blue oven 202, The heating temperature of the second blue oven 202 can be lowered and therefore it is preferable from the viewpoint of suppressing the volatilization or melting loss of the platinum alloy constituting the second blue oven 202.

Subsequently, this molten glass MG is introduced into the second blue sign 202.

The second blue circle 202 is different from the first blue circle 204 in that the upper open space inside the second blue circle 202 is an atmosphere space of a gaseous phase and the bubble B in the molten glass MG flows into the liquid surface So that the molten glass can be discharged to the outside of the molten glass MG.

In the second blue sign 202, the molten glass MG is continuously maintained at a high temperature of 1630 ° C or more by heating the platinum or platinum alloy tube, which is the body of the second blue sign 202, And the molten glass MG is defoamed by blowing on the surface of the molten glass MG. In particular, when the molten glass MG is heated to 1630 캜 or higher (for example, from 1630 to 1700 캜), SnO ₂ accelerates the reduction reaction. At this time, for example, in the case of producing a glass plate for a flat panel display such as a liquid crystal display, the viscosity of the glass becomes 200 to 800 poise suitable for lifting and defoaming of the bubble B by raising the temperature of the molten glass MG have.

Here, the gas component scattered and discharged in the upper open space above the second blue sign 202 is discharged from the gas discharge port (not shown) to the outside of the second blue sign 202. In the second blue sign 202, the molten glass MG from which the bubbles B having a large diameter and which has a high flotation speed due to the floating and defoaming of the bubbles B is introduced into the third blue sign 205.

In the present embodiment, for example, as shown in FIG. 3, the second blue sign 202 to the third blue sign 205 are formed by two platinum or platinum alloy tubes extending in the longitudinal direction of the main body The temperature of the molten glass MG may be raised by controlling the currents flowing through the different regions. In addition, the temperature of the molten glass MG may be raised by controlling currents respectively flowing to three or more different regions extending in the longitudinal direction of the platinum or platinum alloy tube constituting the body of the blue sign.

In this way, it is preferable that the elevation of the molten glass MG is carried out by controlling the currents flowing respectively in at least two different regions of the blue sign, in view of efficient defoaming processing.

In the third blue circle 205, the molten glass MG is cooled by cooling the platinum or platinum alloy tube, which is the body of the third blue circle 205, or by suppressing the degree of heating of the third blue circle 205 . Since the temperature of the molten glass MG is lowered by this cooling, the rising and defoaming of the bubbles B are not performed, the pressure of the gas components in the remaining small bubbles B is lowered, and the bubble diameter is gradually decreased. Further, when the temperature of the molten glass below the MG 1600 ℃, a part of the SnO obtained in the reduction reaction of SnO ₂ in the degassing treatment is to absorb oxygen, it is to go back to the SnO _2. As a result, oxygen, which is a gas component in the bubble B, is reabsorbed in the molten glass MG, and the bubble B becomes smaller and is absorbed in the molten glass MG and finally lost. At this time, the molten glass MG is cooled at a temperature of 1600 DEG C to 1500 DEG C at an average of 2 DEG C / min or more, more preferably at an average of 3 DEG C / min or more. In addition, since the third blue sign 205 is smaller in cross section than the second blue sign 202, the molten glass MG can be efficiently cooled as compared with the second blue sign 202. In other words, it is preferable to cool the temperature of the molten glass MG in the third blue sign 205, rather than to cool the temperature of the molten glass MG in the second blue sign 202, .

In the example shown in Fig. 3, the blue sign for performing the freeness process is divided into three parts: a first blue sign 204, a second blue sign 202 and a third yellow sign 205, Of course, it can be further subdivided. It is possible to more finely adjust the temperature of the molten glass MG by finely dividing the blue sign. Particularly, refinement of the blue sign is advantageous in that it is easy to adjust the temperature in the case of changing the kind and the dissolution amount of the molten glass MG.

In the above description, for the sake of simplicity, the molten glass MG is heated to 1,630 DEG C in the first blue ozone 204, the bubbles B of the molten glass MG are lifted and removed in the second blue ozone 202, In the three-color sign 205, the functions are separately described for each blue sign so that the molten glass MG absorbs the bubble B by the cold temperature of the molten glass MG. However, the function may not be completely divided for each blue sign. The portion of the second blue sign 202 up to the middle in the longitudinal direction may be configured to raise the temperature of the molten glass MG or may be set in the middle of the longitudinal direction of the second blue sign 202, To be a portion for starting the lowering of the temperature of the molten glass MG.

In the present embodiment, the surface temperature of the first blue sign 204, the second blue sign 202, and the third blue sign 205, that is, the surface temperature outside the blue sign, in which the molten glass MG does not flow, The temperature raising rate and the temperature raising rate of the molten glass MG can be managed. The surface temperature of the first blue circle 204, the second blue circle 202 and the third blue circle 205 and the surface temperatures of the first blue circle 204, the second blue circle 202 and the third blue circle 205 (The average value of the temperature of the molten glass MG having the temperature distribution in the blue sign) of the molten glass MG flowing in the molten glass MG flowing in the molten glass MG Can be calculated in advance. Therefore, from the measured surface temperature outside the blue sign, the relationship between the temperature rise rate and the temperature decrease rate can be calculated to manage the temperature increase rate and the temperature decrease rate. The flow velocity of the molten glass MG can be calculated from the volume of each apparatus and the amount of molten glass MG per unit time flowing into the molding apparatus 300. Further, the temperature of the molten glass MG can be calculated from the viscosity and the thermal conductivity of the glass.

Thus, the temperature of the molten glass MG after the defoaming treatment is lowered at a temperature lowering rate of, for example, 2 deg. C / min or more from 1600 deg. C to 1500 deg. C, as described later, This is to reduce the number of bubbles per mass. The bubble referred to herein means a bubble having a volume equal to or larger than a volume of a predetermined bubble, for example, a volume of bubble having a diameter of 20 mu m.

Further, the faster the cooling rate is, the smaller the number of the bubbles remaining in the glass plate. However, this reduction effect decreases with the increase of the cooling rate. It is preferable that the temperature lowering rate is 3 deg. C / min or more. The upper limit of the temperature lowering rate is not particularly set. However, when the glass plate is manufactured industrially, the upper limit is 50 DEG C / min for the following reasons.

That is, if the cooling rate of the molten glass MG becomes too fast, the phenomenon that oxygen in the bubble B of the molten glass MG is reabsorbed by the molten glass MG is inhibited, and as a result, there is a possibility that the bubble B itself in the molten glass MG is not reduced have. Further, since the thermal conductivity of the glass is as small as about 20 to 50 W / (m 占 에서도) even at a high temperature, the rapid cooling of the molten glass MG can be performed only at the outside of the third blue sign 205 Only the molten glass MG near the outer surface of the third blue circle 205 is cooled and the molten glass MG in the center portion of the third blue circle 205 is maintained at the high temperature state . That is, the temperature difference between the outer surface portion and the center portion of the molten glass MG becomes large in the third blue circle 205. In this case, there arises a problem that crystals are precipitated from the molten glass MG on the outer surface portion. When the molten glass MG is stirred in a state in which the temperature difference of the molten glass MG between the outer surface portion and the central portion of the molten glass MG is large in the third glass oven 205, the glass having a large temperature difference is mixed, In addition, it is easy to inhibit the homogeneity in the composition of the glass. In order to accelerate the temperature lowering rate of the molten glass MG, it is necessary to increase the heat radiation from the third blue ozone 205. Therefore, the back brick for supporting the main body of the platinum or platinum alloy tube of the third blue ozone 205 The thickness of the supporting member must be reduced. However, the strength of the facility is reduced by the amount of thinning of the supporting member. Thus, in the case of industrially producing a glass plate, unnecessarily accelerating the rate of temperature decrease of the molten glass MG causes only the above-described problems, which can not be said to be valid.

From the above, it is preferable that the upper limit of the temperature lowering rate of the molten glass MG to 1600 占 폚 to 1500 占 폚 is 50 占 폚 / min, more preferably 35 占 폚 / min. That is, in this embodiment, the cooling rate is preferably 2 ° C / min to 50 ° C / min, more preferably 2.5 ° C / min to 50 ° C / min, more preferably 3 ° C / min to 35 ° C / desirable.

(Molding step)

Fig. 4 is a view mainly showing a configuration of a device for performing a molding step and a cutting step. The molding apparatus 300 includes a molding furnace 340 and a annealing furnace 350.

The molding furnace 340 and the annealing furnace 350 are surrounded by a furnace wall (not shown) made of refractory material such as refractory bricks. The shaping furnace 340 is vertically upwardly provided with respect to the slow cooling furnace 350. The molding body 310, the atmosphere partitioning member 320, the cooling roller 330, the cooling unit 335, and the cooling unit 330 are disposed in a furnace inner space surrounded by the furnace walls of the forming furnace 340 and the annealing furnace 350, And conveying rollers 350a to 350d are provided.

The molded body 310 forms the molten glass MG flowing from the dissolving apparatus 200 through the glass supply pipe 206 shown in Fig. The molten glass to be supplied to the molded body 310 has a temperature at log? = 4.3 to 5.7 with respect to the viscosity? (Poise). The temperature of the molten glass MG differs depending on the kind of the glass, but is, for example, 1200 to 1300 占 폚 for a glass for a liquid crystal display. In this way, in the molding apparatus 300, the flow of the plate-like glass G in the vertical direction is made. The molded body 310 is an elongated structure made of refractory bricks or the like, and has a wedge-shaped cross section as shown in Fig. A supply groove 312 serving as a flow path for guiding the molten glass is formed in the upper portion of the formed body 310. The supply groove 312 is connected to the third charging ring 205 in the supply port provided in the molding apparatus 300 and the molten glass MG flowing through the third charging ring 205 is connected to the supply groove 312 Ride and flow. The supply groove 312 is formed so that the molten glass MG overflows from the supply groove 312.

The molten glass overflowing from the supply grooves 312 flows down along the vertical wall surface and the inclined wall surface of the side walls on both sides of the formed body 310. The molten glass that has flowed through the side walls merges at the lower end 313 of the formed body 310 shown in Fig. 4, and one plate glass G is molded.

(Glass composition)

The glass plate produced by the glass plate manufacturing method of the present embodiment is suitably used for a glass substrate for a flat panel display. For example, even if Li ₂ O, Na ₂ O and K ₂ O are substantially not contained, or at least one of Li ₂ O, Na ₂ O and K ₂ O is contained , Li ₂ O, Na ₂ O and K ₂ O is not more than 2% by mass is preferable from the viewpoint of effectively exhibiting the effect of the present embodiment. The composition of the glass is appropriately exemplified as follows.

(a) 50 to 70% by mass of SiO ₂ ,

(b) 5 to 18 mass% of B ₂ O ₃ ,

(c) 10 to 25% by mass of Al ₂ O ₃ ,

(d) 0 to 10% by mass of MgO,

(e) 0 to 20% by mass of CaO,

(f) 0 to 20 mass% of SrO,

(g) BaO: 0 to 10% by mass,

(h) RO: 5 to 20 mass% (R is at least one selected from Mg, Ca, Sr and Ba, RO is the total of components including MgO, CaO, SrO and BaO)

(i) R ' ₂ O: more than 0.1 mass% and not more than 2.0 mass% (provided that R' is at least one selected from Li, Na and K and R ' ₂ O is Li ₂ O, Na ₂ O and K ₂ O)),

(j) at least one kind of metal oxide selected from SnO ₂ , Fe ₂ O ₃ and cerium oxide in a total amount of 0.05 to 1.5 mass%

In addition, the compositions of (i) and (j) are not essential, but may include the compositions of (i) and (j). The above glass contains substantially no As ₂ O ₃ and PbO but contains SnO ₂ . Further, from the viewpoint of environmental problems, it is preferable that Sb ₂ O ₃ is substantially not contained.

The content of R ' ₂ O in (i) may be 0 mass%.

In addition to the above-mentioned components, the glass plate of this embodiment may contain various other oxides to control various physical properties of the glass, melting, refining and molding. Examples of such other oxides include, but are not limited to, TiO ₂ , MnO, ZnO, Nb ₂ O ₅ , MoO ₃ , Ta ₂ O ₅ , WO ₃ , Y ₂ O ₃ and La ₂ O ₃ .

In the present embodiment, since SnO ₂ is a component which makes the transparency of the glass easier to lose, the content thereof is preferably 0.01 to 0.5% by mass, more preferably 0.05 to 5% by mass in order not to cause transparency loss while enhancing clarity. More preferably 0.3% by mass, and still more preferably 0.1% by mass to 0.3% by mass.

Fe ₂ O ₃ is a component for increasing the infrared absorption of glass, and by containing Fe ₂ O ₃ , defoaming can be promoted. However, Fe ₂ O ₃ is a component that lowers the transmittance of glass. Therefore, if the content of Fe ₂ O ₃ is excessively large, it becomes unsuitable for a display glass substrate. From the above, when Fe ₂ O ₃ is contained in the metal oxide, it is preferable that the content of Fe ₂ O ₃ is 0.01 to 0.1% by mass from the viewpoint of suppressing lowering of the transmittance of the glass while improving refinability , And more preferably 0.01 to 0.08 mass%. From the viewpoint that the defoaming process is completed in a short time by enhancing the refineness and the occurrence of SO ₂ bubbles in the absorption process is suppressed, it is preferable that 0.01 to 0.5 mass% of SnO ₂ and 0.01 to 0.1 mass% of Fe ₂ O ₃ It is preferable to use them in combination.

In addition, since R ' ₂ O in (i) is a component that elutes from the glass to deteriorate the characteristics of the TFT and may increase the coefficient of thermal expansion of the glass to damage the substrate during heat treatment, When it is applied as a glass substrate or a glass substrate for an organic EL display, it is preferably not substantially contained. However, by containing a specific amount of the above-described components in the glass, it is possible to raise the basicity of the glass while suppressing the thermal expansion of the glass within a certain range without causing deterioration of the characteristics of the TFT, , And it is possible to exert the clarity. In addition, R ' ₂ O can lower the electrical resistivity of the glass and improve the solubility. Therefore, R ' ₂ O is preferably 0 to 2.0% by mass, more preferably 0.1 to 1.0% by mass, and most preferably 0.2 to 0.5% by mass. In addition, it is preferable to not contain Li ₂ O and Na ₂ O, and to contain K ₂ O, which is most likely to elute from the glass to cause deterioration of TFT characteristics, among the above components. The content of K ₂ O is preferably 0 to 2.0% by mass, more preferably 0.1 to 1.0% by mass, still more preferably 0.2 to 0.5% by mass.

In order to obtain the property that the glass plate of the present embodiment is suitably used as a glass substrate used for a liquid crystal display or an organic EL display or the like, it is preferable that the viscosity at the refining temperature of the glass melt MG is higher than that of a glass plate containing a large amount of alkali So that the bubble floatation rate tends to be slowed in the defoaming treatment. In particular, since a glass substrate for forming a low-temperature polysilicon TFT on a glass surface is required to have a high strain point, the high-temperature viscosity tends to be high, and the viscosity at the refining temperature of the molten glass MG is further increased. For this reason, for example, in the case of producing a glass having a strain point of 680 DEG C or higher, particularly a strain point of 690 DEG C or higher, the rate of rise of bubbles tends to be slower in the defoaming treatment. When the glass plate of the present embodiment is a glass substrate constituting a liquid crystal display or an organic EL display, it is preferable that the viscosity of the molten glass MG at a temperature of, for example, 1630 캜 is 130 to 350 poise. When the glass temperature of the glass constituting the glass substrate is in the range of 1550 to 1680 캜 when the glass viscosity is log 侶 = 2.5, the present embodiment is suitable and if the glass temperature is in the range of 1570 캜 to 1680 캜, And the effect of the present embodiment becomes more remarkable in the range of 1590 캜 to 1680 캜.

 (Temperature history of the molten glass)

5 is a view for explaining an example of the temperature history from the dissolving process to the forming process in the present embodiment.

The glass raw materials used in the production of the glass sheet of the present embodiment are weighed and mixed well with various raw materials so as to have the aimed chemical composition, and glass raw materials are produced. At that time, SnO ₂ is added to the glass raw material in a predetermined amount as a fining agent. The thus-produced glass raw material to which SnO ₂ is added is introduced into the dissolution tank 201 and dissolved at least by conduction heating, whereby molten glass MG is produced. The glass raw material charged into the melting tank 201 is decomposed at the point when it reaches the decomposition temperature of the component, and becomes a molten glass MG by the vitrification reaction. The molten glass MG proceeds from the vicinity of the bottom of the melting tank 201 to the first blue sign 204 (glass feed pipe 204) while gradually increasing the temperature while flowing through the melting tank 201.

Therefore, in the melting tank 201, the temperature of the molten glass MG gradually decreases from the temperature T1 at the time of the introduction of the glass raw material to the temperature T3 at the time of entering the first blue sign 204 (the glass supply pipe 204) Lt; / RTI &gt; 5, T1 <T2 <T3, but T2 = T3 or T2> T3, or at least T1 <T3.

A constant electric current is flowed between a metal flange (not shown) of the first blue oven 204 and a metal flange (not shown) of the second blue oven 202 so that the platinum or platinum alloy tube of the first blue oven 204 is energized A certain current is flown between the metal flange (not shown) of the second blue oven 202 and the other metal flange (not shown) of the second blue oven 202 to heat the platinum of the second blue oven 202 The molten glass MG entering the first blue circle 204 is heated to a temperature T4 at which SnO ₂ abruptly releases oxygen from the temperature T3 (for example, 1630 DEG C or higher and 1630 to 1700 DEG C More preferably from 1650 to 1700 캜), and the temperature is raised at a rate of temperature increase of 2 캜 / minute or more. The reason why the temperature raising rate is 2 ° C / min or more is that, as will be described later, when the temperature raising rate is 2 ° C / min or more, the discharge amount of O ₂ gas increases sharply. Further, the larger the difference between the temperature T3 and the temperature T4 is, the more the amount of O ₂ released by SnO ₂ in the molten glass MG is increased and the defoaming is accelerated. For this reason, it is preferable that the temperature T4 is, for example, about 50 DEG C higher than the temperature T3.

Further, the molten glass MG entering the second blue sign 202 is maintained at a temperature T5 substantially equal to the temperature T4 from the temperature T4. In the present embodiment, the temperature is controlled at the temperature T3 to the temperature T5 by employing a method of energizing each blue sign, but the present invention is not limited to this method. For example, the temperature may be adjusted by indirect heating by a heater (not shown) disposed around each blue circle.

At this time, the molten glass MG is heated to 1,630 캜 or higher, thereby promoting the reduction reaction of SnO _{2 as} a clarifying agent. As a result, a large amount of oxygen is released into the molten glass MG. The existing bubbles B in the molten glass MG are formed in such a manner that the bubbling diameter is increased by the synergistic effect of the pressure of the gas component in the bubbles B due to the temperature rise of the molten glass MG, B, and the bubble diameter is enlarged by this synergistic effect.

As the bubble diameter B is increased, the bubble B is lifted at a faster rate in accordance with the Stokes' law, so that the bubble B is lifted and faded.

Since the molten glass MG is also maintained at a high temperature of 1630 DEG C or higher in the second blue circle 202, the bubbles B in the molten glass MG float on the surface of the molten glass MG and are scattered on the surface of the molten glass MG, Degassing of the glass MG is carried out.

5, the degassing process is performed in a period in which the temperature of the molten glass MG rises from the temperature T3 to the temperature T4 and thereafter is maintained at the temperature T5 substantially equal to the temperature T4. In Fig. 5, T4 and T5 are substantially the same, but T4 < T5, and T4 > T5.

In addition, although the temperature of the molten glass MG reaches the temperature T4 in the example of the first blue circle 204, it may be in the second blue circle 202 as well.

The first maximum temperature of the molten glass when the molten glass MG flows through the first observer 204 is equal to the second highest temperature of the molten glass MG when flowing through the second observer 202, Higher than that is desirable. Thereby, when the molten glass moves from the first blue circle 204 to the second blue circle 202, the temperature of the molten glass is sufficiently high and is maintained above the temperature at which the reduction reaction of the fining agent occurs, Blue sign 202 does not require heating to further raise the molten glass. As a result, the heating temperature of the second blue sign 202 can be suppressed to be lower than the conventional one. Accordingly, it is possible to suppress the volatilization of platinum from the second blue ozone 202 composed of platinum or a platinum alloy, and to prevent the foreign matter such as platinum crystals adhering to the inner wall surface in the second purifying tube 202 from being melted It is possible to produce a glass sheet having few defects caused by being incorporated into the glass MG, that is, a defect caused by the foreign matter. It is preferable that the temperature of the molten glass MG reaches the first highest temperature while the molten glass MG flows through the first blue sign 204. [ In this case, compared to the case where the molten glass reaches the first maximum temperature and the second maximum temperature at the connection position of the first blue sign 204 and the second blue sign 202, the heating of the second blue sign 202 The temperature is lowered, so that the volatilization of platinum can be more easily suppressed from the second blue ozone 202 composed of platinum or a platinum alloy.

Next, the molten glass MG proceeding from the second blue sign 202 to the third blue sign 205 is heated to a temperature T6 (for example, 1600 占 폚) from the temperature T5 to absorb the remaining bubble B Thus, it is cooled to the temperature T7 (temperature suitable for the stirring process, which varies depending on the type of glass and the stirring apparatus, for example, 1500 DEG C).

When the temperature of the molten glass MG is lowered, the bubbles B do not rise and disappear, and the pressure of the gas components in the small bubbles remaining in the molten glass MG also decreases, and the bubble diameter gradually decreases. In addition, when the melting temperature of the glass below the MG 1600 ℃, to a part of the SnO (that obtained by reduction of SnO ₂₎ absorbs oxygen, and go back to the SnO _2. As a result, the oxygen remaining in the bubbles B in the molten glass MG is reabsorbed in the molten glass MG, and the small bubbles become smaller. The small bubbles are absorbed by the molten glass MG, and the small bubbles finally disappear.

The treatment for absorbing O ₂ which is a gas component in the bubble B by the oxidation reaction of SnO is an absorption process and is performed in a period in which the temperature decreases from the temperature T5 to the temperature T7 via the temperature T6. In Fig. 5, although the rate of decrease in temperature T5 to T6 is faster than the rate of decrease in temperature T6 to T7, the rate of decrease in temperature T5 to T6 may be lower than the rate of decrease in temperature T6 to T7 . At least during this absorption process, it is preferable that the temperature of the molten glass MG is lowered at a temperature lowering rate of 2 DEG C / min or more in a temperature range of 1600 DEG C to 1500 DEG C. However, in view of increasing the rate of temperature drop when the molten glass MG is in a higher temperature state, reducing the diffusion of SO ₂ , which will be described later, and reducing SO _{2 introduced} into the bubble B, It is preferable that the speed is faster than the rate of decrease in temperature from T6 to T7. That is, in the absorption process, the temperature of the molten glass MG in the temperature range of 1500 占 폚 or lower (specifically, the range from 1500 占 폚 to the molten glass temperature when it is supplied to the molding step, for example, 1500 占 폚 to 1300 占 폚) The cooling rate is preferably slower than the cooling rate in the temperature range of 1600 캜 to 1500 캜.

Further, the temperature T6 to by the rate of decline T7 slower than the temperature lowering rate of T5 to T6, while reducing the SO ₂ to be drawn in the cell B, stirring the molten glass MG third blue sign (205 of which flows into the tank (203) (Glass supply pipe 205), the temperature difference between the outer surface portion and the center portion can be reduced.

From the viewpoint of improvement of the productivity of the glass plate and reduction of facility cost, it is preferable that the molten glass MG is in the range of 1,500 DEG C or lower (specifically, the range from 1500 DEG C to the molten glass temperature when supplied to the molding step, For example 1500 占 폚 to 1300 占 폚) is preferably higher than the rate of temperature decrease in the temperature range of 1600 占 폚 to 1500 占 폚. When the temperature control of the molten glass MG is performed, it is preferable to provide a flow rate adjusting device for adjusting the amount of the molten glass MG to be supplied to the molding step.

In addition, since the amount of the molten glass MG supplied to the molding step can be adjusted by the temperature control of the molten glass MG in the glass supply pipe 206 while reducing the amount of SO _{2 introduced} into the bubble B, It is preferable that the rate of decline in the temperature range in which the glass MG is 1500 占 폚 or less is slower than the rate of decline in the temperature range of 1600 占 폚 to 1500 占 폚. This makes it easy to adjust the amount of the molten glass MG flowing into the molding process without processing the glass supply pipe 206 into a special shape or providing a flow rate adjusting device other than the glass supply pipe 206. In addition, the temperature difference between the outer surface portion and the center portion in the glass supply pipe 206 of the molten glass MG flowing into the molding process can be reduced.

After the absorption treatment or during the absorption treatment, the molten glass MG enters the stirring tank 203. The stirring tank 203 reduces the composition unevenness in the molten glass MG to homogenize the molten glass MG. Further, in the stirring tank 203, the above absorption process may be performed continuously. Thereafter, the molten glass MG is cooled until the temperature T8 suitable for molding in the molding step, for example, 1200 to 1300 deg.

As described above, the stirring step of homogenously stirring the components of the molten glass MG between the refining step and the molding step is included. Between the refining step and the forming step means that the timing at which the stirring step is started is between the timing at which the refining step is started and the timing at which the forming step is started. The stirring step of the molten glass MG may be started in the middle of the fining process or may be started after the fining process. Further, in Fig. 1, the clarifying step (ST2) and the homogenizing step (ST3) are shown in the order of the timing of the start timing. In the dissolving step, the molten glass MG is supplied to the refining step at a temperature T3 higher than the temperature T1 at the start of dissolution of the molten glass MG. In the refining step, the molten glass MG is supplied to the stirring step at a temperature lower than the temperature T7. In the stirring step, the molten glass MG is supplied to the molding process at a temperature of log? = 4.3 to 5.7 with respect to the viscosity? (Poise). In the molding process, the molten glass MG is molded into a plate-like glass in a state where the temperature of the molten glass MG is, for example, 1200 to 1300 占 폚. The liquid phase viscosity of the glass plate is preferably log? = 4 or more, and the liquidus temperature of the glass plate is preferably 1050 to 1270 占 폚. By setting the liquidus viscosity and the liquidus temperature as described above, the overflow down-draw method can be applied as a molding method.

FIG. 6 is a graph showing the relationship between the amount of O ₂ released and the rate of temperature rise included in the molten glass when the defoaming treatment is carried out, which is a measurement result made in an experimental work. The temperature raising rate is an average speed in the temperature range of 1550 캜 to 1640 캜. The glass plate used in this measurement had the same glass composition as that of the glass substrate for a liquid crystal display having a small alkali metal content, and SnO ₂ was used as a fining agent. Specifically, the measurement results shown in Fig. 6 were obtained using a glass substrate for a liquid crystal display having the glass composition shown below.

SiO ₂ : 60 mass%

Al ₂ O ₃ : 19.5 mass%

B ₂ O ₃ : 10 mass%

CaO: 5.3 mass%

SrO: 5 mass%

SnO _2: 0.2% by weight

According to Fig. 6, in order to increase the discharge amount of O ₂ , it is found that the rate of temperature rise of the molten glass MG should be 2 ° C / min or more. Further, in the measurement results of Fig. 6, CO ₂ is obtained by sealing a gas (CO ₂ ) in a cavity by laminating another glass substrate on a glass substrate on which cavities are formed, and heating and fusing each glass substrate in this state , And is present as bubbles in the molten glass MG.

In the present embodiment, there is no substantial upper limit of the temperature raising rate, and it may be 10 deg. C / min or less, for example. Since the glass has a low thermal conductivity, it is necessary to increase the heat transfer area in order to increase the heating rate. In order to increase the heat transfer area, the inner diameter of the first blue label 204 or the second blue label 202 as the metal pipe is reduced and the first blue label 204 or the second blue label 202, And long ones in the longitudinal direction. In order to increase the heat transfer area, it is also possible to raise the temperature of the first blue sign 204 or the second blue sign 202 to a temperature significantly higher than the temperature of the molten glass MG. However, if the inner diameter of the first blue sign 204 or the second blue sign 202 is reduced and the first blue sign 204 or the second blue sign 202 is formed long in the longitudinal direction, The manufacturing apparatus becomes large, which is not preferable. If the temperature of the first blue sign 204 or the second blue sign 202 is raised to a temperature significantly higher than the temperature of the molten glass MG, there is a possibility that the glass plate manufacturing apparatus is broken by the high temperature. Therefore, it is preferable that the substantial upper limit of the temperature raising rate is 10 DEG C / min or less. Therefore, the temperature raising rate is preferably 2 ° C / min to 10 ° C / min, more preferably 3 ° C / min to 8 ° C / min, and further preferably 3 ° C to 6.5 ° C / min. In this range, the defoaming treatment is efficiently performed, and the bubbles remaining on the glass plate can be efficiently reduced.

Further, as described above, in the bubble absorption treatment performed after the degassing treatment, the molten glass MG is cooled at a temperature lowering rate of 2 DEG C / min or more in the temperature range of 1600 DEG C to 1500 DEG C. This is done for the reasons explained below.

Because the from temperature T3 raising the temperature of the molten glass MG to a temperature T4 period, SnO ₂ is the melt to more than 1600 to 1630 ℃ temperature is reduced to release oxygen free MG is raised up to temperature T5, the bubbles in the molten glass MG, SnO ₂ diffused in the molten glass MG is promoted, and the diffusion of O ₂ , CO ₂ , and SO ₂ dissolved in the molten glass MG is accelerated. In addition, O ₂ , CO ₂ and SO ₂ are also introduced. The solubility of the gas component in the molten glass MG varies depending on the glass component. In the case of SO ₂ , the solubility of the gas component in the molten glass MG is relatively high in the case of glass having a large content of alkali metal. However, In the glass plate used for the glass substrate for a liquid crystal display as in the present embodiment, the solubility that can be dissolved in the molten glass MG is low. In the glass plate used for the liquid crystal display glass substrate, the S (sulfur) component is not artificially added as a glass raw material, but the glass gas used as the impurity in the raw material or the combustion gas , Propane gas, etc.) as impurities. As a result, the S component contained as these impurities is oxidized to SO ₂ , diffused into the bubble B contained in the molten glass MG, and is drawn in. Since SO ₂ is difficult to be reabsorbed, it remains as bubble B. This phenomenon appears to be very conspicuous as compared with the conventional use of As ₂ O ₃ as the fining agent.

In the case of the glass composition using SnO ₂ as the refining agent, the longer the holding time at the high temperature of the molten glass MG is, the more the diffusion of SO ₂ into the existing bubble B in the molten glass MG is promoted. This is considered to be because the temperature became high and the diffusion rate of SO _{2 in} the molten glass MG became faster and it became easy to enter the bubble B.

In addition, the longer the time the temperature of the molten glass MG is maintained at temperatures higher than 1630 ℃, the molten glass MG is extremely reduced, in the course of conducting the temperature decrease of the molten glass MG, is easy to the SO ₂ bubbling. On the other hand, if the holding time at 1630 DEG C or more is too short, defoaming in the defoaming process becomes insufficient. Therefore, the time for maintaining the temperature of the molten glass MG at 1630 DEG C or higher is preferably 15 minutes to 90 minutes, and more preferably 30 minutes to 60 minutes.

Thereafter, when the temperature of the molten glass MG is lowered from the temperature T5 to the temperature T7, the SnO ₂ obtained by the reduction of SnO ₂ absorbs O ₂ by the oxidation reaction and tries to oxidize it. Therefore, O ₂ in the bubble B remaining in the molten glass MG is absorbed by SnO. However, the diffusion of SO ₂ or CO ₂ in the molten glass MG into the existing bubble B is still maintained. Therefore, the gas components in the cell B in the period from the temperature T5 is the temperature T7, than the duration of temperature T5 from the temperature T3 higher the concentration of SO _2, CO _2. Particularly, in the molten glass MG used in the present embodiment, since the content of the alkali metal is small, the solubility of SO _{2 in} the molten glass MG is small. Therefore, once the SO ₂ is drawn into the bubble B as a gas, the SO ₂ is hardly absorbed into the molten glass MG in the absorption process.

As described above, in the period from the temperature T5 to the temperature T7, the O ₂ in the bubble B is absorbed by SnO due to the oxidation reaction of SnO, but since the diffusion of SO ₂ and CO ₂ into the existing bubble B is still maintained, The diffusion of SO ₂ and CO ₂ into the existing bubble B can be reduced and the growth of the bubble B can be suppressed. Therefore, during the period of the absorption treatment of the temperature T5 to the temperature T7, the molten glass MG is cooled at a temperature lowering rate of 2 DEG C / min or more in the temperature range of 1600 DEG C to 1500 DEG C to suppress the number of bubbles in the glass plate .

Fig. 7 is a graph showing the results of measurement of the content of SO ₂ contained in the holes in which the bubbles B in the glass are reproduced, showing the dependence of the content of SO ₂ on the temperature condition of the glass and the temperature holding time. The size of the black circles in FIG. 7 represents the size of the bubble B and represents the content of SO ₂ .

The glass plate has the same glass composition as the above-mentioned glass substrate for a liquid crystal display having a small alkali metal content, and contains SnO ₂ as a fining agent. Specifically, a glass substrate for a liquid crystal display having a glass composition similar to that of the glass plate produced when obtaining the measurement results of FIG. 6 was used.

Holes filled with O ₂ were reproduced as bubbles by artificially drilling holes in a glass plate molded into a plate shape of molten glass of this glass composition and sandwiching the holes with glass plates of the same kind of glass composition in oxygen atmosphere on both sides of the glass plate . Heating the glass plate having the holes, changing the temperature and the temperature holding time of more than 1200 ℃ in various, and the content of SO ₂ in the hole was determined by gas analysis. Since the glass plate is heated at 1200 DEG C or higher, the glass plate is in a molten state, and the bubble B remaining in the molten glass can be reproduced.

According to Fig. 7, it can be seen that SO ₂ is contained in the hole filled with O _{2 at} a temperature of about 1500 ° C or higher. In particular, it can be seen that the higher the temperature and the longer the temperature holding time, the higher the content of SO ₂ . This means that the diffusion of dissolved SO _{2 in} the molten glass is promoted by the high temperature and enters the hole.

Therefore, it is preferable that the molten glass MG is rapidly lowered to less than 1500 DEG C in the absorption treatment after the degassing treatment. In the present embodiment, the molten glass MG has a temperature lowering rate of 2 DEG C / min or more in the temperature range of 1600 DEG C to 1500 DEG C .

Fig. 8 is a graph showing the measurement results showing the relation between the bubble level and the temperature drop rate generated when a glass plate was manufactured in an experiment in which the temperature history of the molten glass MG shown in Fig. 5 was simulated. The cooling rate is an average speed in a temperature range of 1600 캜 to 1500 캜. The produced glass plate had the same glass composition as the glass substrate for a liquid crystal display having a small alkali metal content, and SnO ₂ was used as a fining agent. Specifically, a glass substrate for a liquid crystal display having a glass composition similar to that of the glass plate produced when obtaining the measurement results of FIG. 6 was used.

When the cooling rate is less than 2 캜 / minute, it can be seen that the bubble level rises sharply. The bubble level indicates how much the bubble number will deteriorate based on the number of bubbles per unit glass mass when the cooling rate is set at 10 占 폚 / min. For example, the bubble level 3 means the number of bubbles that is three times the number of bubbles when the rate of temperature decrease is set to 10 ° C / min. Therefore, when the cooling rate is less than 2 캜 / minute, it can be seen that the number of bubbles increases sharply.

According to Fig. 8, in order to reduce the number of bubbles, it is preferable that the rate of temperature decrease is 2 DEG C / min or more.

(Example 1)

9 is a graph showing the measurement results showing the relationship between the number of bubbles present in the glass plate and the temperature drop rate when the glass plate is manufactured using the apparatus for producing the glass plate shown in Fig. After a dissolution step, a refining step and a stirring step, a glass plate was produced by an overflow down-draw method. At this time, the temperature history of the molten glass MG took the history shown in Fig. 5 except for the temperature decreasing rate. The cooling rate is an average speed in the temperature range of 1600 캜 to 1500 캜. The produced glass plate had the same glass composition as the glass substrate for a liquid crystal display having a small alkali metal content, and SnO ₂ was used as a fining agent. Specifically, a glass substrate for a liquid crystal display having a glass composition similar to that of the glass plate produced when obtaining the measurement results of Fig. 6 was used. The bubble level shown in Fig. 9 indicates how much the bubble number is deteriorated based on the number of bubbles per unit mass when the rate of temperature decrease is 8.4 DEG C / min. For example, the bubble level 5 means that the number of bubbles is five times the number of bubbles when the rate of temperature decrease is 8.4 DEG C / min. The bubble level at a cooling rate of 7.9 DEG C / min is 1.1, the bubble level at a cooling rate of 4.9 DEG C / min is 1.6, the bubble level at a cooling rate of 4.2 DEG C / min is 1.8, The bubble level was 1.8. On the other hand, the bubble level at a cooling rate of 1.8 ° C / min is 3.0, the bubble level at a cooling rate of 0.5 ° C / min is 83, and the bubble level is 3 times or more the number of bubbles when the cooling rate is 8.4 ° C / Was included.

According to Fig. 9, when the cooling rate is less than 2 DEG C / min, it is understood that the bubble level abruptly rises and the bubble number abruptly rises. Therefore, it can be seen that when the molten glass MG is cooled down at a temperature lowering rate of 2 DEG C / min or more, more preferably 2.5 DEG C / min or more in the temperature range of 1600 DEG C to 1500 DEG C, the number of bubbles is reduced. From Fig. 9, it can be seen that the cooling rate is more effective in reducing the number of bubbles at a cooling rate of 3 DEG C / min to 8 DEG C / min, for example. Further, SiO _2: 60 mass%, Al ₂ O _3: 19.5 wt%, B ₂ O _3: 10 mass%, CaO: 5.3% by weight, SrO: 5% by weight, SnO _2: 0.15 mass%, Fe ₂ O ₃ : 0.05% by mass, the bubble count decreased slightly in total, but almost the same results were obtained. Further, SiO _2: 61 mass%, Al ₂ O _3: 19.5 wt%, B ₂ O _3: 10 mass%, CaO: 9 mass%, SnO _2: 0.3 mass%, R ₂ O (R is, Li, Na , A glass plate having a total content of K in the glass plate): 0.2% by mass (strain point: 700 ° C).

(Example 2)

10 is a graph showing the relationship between the number of bubbles present in the glass plate and the temperature raising rate. The produced glass plate had the same glass composition as the glass substrate for a liquid crystal display having a small alkali metal content, and SnO ₂ was used as a fining agent. Specifically, a glass substrate for a liquid crystal display having a glass composition similar to that of the glass plate produced when obtaining the measurement results of FIG. 6 was used. The glass raw material thus combined with the above glass composition was melted at 1580 ° C (= T3) and then heated to 1640 ° C (= T4). The temperature was lowered at a rate of 10 DEG C / minute to 1600 DEG C (= T6), and then decreased again at a rate of 5 DEG C / minute until 1500 DEG C (= T5). At this time, the heating rate was changed from 0.5 ° C./minute, 1 ° C./minute, 1.5 ° C./minute, 2 ° C./minute, 3 ° C./minute, 4 ° C./minute, 5 ° C./minute and 6 ° C./minute, Changes were observed. The bubble level shown in Fig. 10 shows how much the bubble number is deteriorated based on the number of bubbles per unit mass when the rate of temperature rise is 2 캜 / minute. For example, the bubble level 5 means that the number of bubbles is five times the number of bubbles when the rate of temperature increase is 2 ° C / min. The bubble level at a heating rate of 2 ° C / min is 1, the bubble level at a rate of temperature rise of 3 ° C / min is 0.8, the bubble level at a rate of temperature increase of 4 ° C / min is 0.7, The bubble level was 0.7, and the bubble level at a temperature raising rate of 6 캜 / min was 0.6. On the other hand, the bubble level at a heating rate of 0.5 ° C / min was 4.8, the bubble level at a heating rate of 1 ° C / min was 2.3, the bubble level at a heating rate of 1.5 ° C / min was 1.6, Minute, the bubbles contained 1.5 times or more of the number of bubbles.

According to Fig. 10, when the heating rate is less than 2 DEG C / min, the bubble level rises sharply and the bubble number increases sharply. Therefore, it is understood that, after the melting process, when the temperature of the molten glass MG is raised at a rate of 2 ° C / min or more, more preferably 2.5 ° C / min or more until the temperature of the molten glass MG becomes 1630 ° C or more, the number of bubbles is reduced. Therefore, it is preferably 2 ° C / min to 10 ° C / min, more preferably 3 ° C / min to 8 ° C / min, and further preferably 3 ° C to 6.5 ° C / min. 10, for example, a temperature raising rate of 3 ° C / min to 8 ° C / min, 3 ° C / min to 6 ° C / min, 4 ° C / min to 6 ° C / min, Deg.] C / minute, which is effective in reducing the number of bubbles. Further, SiO _2: 60 mass%, Al ₂ O _3: 19.5 wt%, B ₂ O _3: 10 mass%, CaO: 5.3% by weight, SrO: 5% by weight, SnO _2: 0.15 mass%, Fe ₂ O ₃ : 0.05% by mass, the bubble count decreased slightly in total, but almost the same results were obtained. Further, SiO _2: 61 mass%, Al ₂ O _3: 19.5 wt%, B ₂ O _3: 10 mass%, CaO: 9 mass%, SnO _2: 0.3 mass%, R ₂ O (R is, Li, Na , A glass plate having a total content of K in the glass plate): 0.2% by mass (strain point: 700 ° C).

As described above, according to the present embodiment, since the number of SO ₂ bubbles in the molten glass can be reduced, the bubbles as cavitation nuclei generated by the stirring blade rotation in the stirring step can also be reduced, The number can be reduced. This effect becomes more remarkable in a method for producing a glass sheet having a small content of BaO or SrO as a glass composition.

More specifically, MgO, CaO, SrO, and BaO contained in the glass composition are often added to the raw material as a carbonate, and the decomposition temperature thereof is lowest in the order of MgO, higher in the order of CaO, SrO, and BaO. That is, the higher the decomposition temperature, the higher the temperature at which CO ₂ starts to emit. As is apparent from the above, when the molten glass MG is cooled down after the defoaming treatment, the higher the decomposition temperature, the more CO ₂ begins to be absorbed at a higher temperature. For example, BaO starts to absorb CO ₂ at around 1300 ° C.

However, as the glass composition produced in relatively high temperature region small when the content of BaO and SrO is the absorption of CO ₂ starts a glass substrate, the absorption of CO _2, and then lowering the temperature of the molten glass MG, i.e., the molten glass MG Lt; RTI ID = 0.0 &gt; viscosity. &Lt; / RTI &gt; Here, the lower the viscosity of the molten glass MG, the faster the CO ₂ diffuses into the molten glass MG. As a result, in the production method of the glass plate in which the viscosity of the molten glass MG is increased (the temperature is lowered) and the absorption of CO ₂ is started, CO ₂ is likely to remain in the molten glass MG as bubbles.

It is possible to reduce the amount of SO ₂ existing as a gas component of the bubbles in the molten glass as in the present embodiment. Even in the production of a glass plate in which CO ₂ is likely to remain as described above, As a result, the number of bubbles in the glass plate as the final product can be reduced. From the above, the present embodiment is suitable for producing a glass substrate having a BaO content of 0 to 1.0 mass%, and is more suitable for a glass substrate production method substantially containing no BaO. Further, the present embodiment is suitable for producing a glass substrate having a SrO content of 0 to 3.0 mass%, and is more suitable for a method of manufacturing a glass substrate substantially containing no SrO.

Although the method of manufacturing the glass plate of the present invention has been described in detail, the present invention is not limited to the above-described embodiment, and various modifications and changes may be made without departing from the gist of the present invention.

200: dissolution apparatus
201: Melting bath
202: Blue sign
203: stirring tank
203a: stirrer
204, 205, 206: glass supply pipe
300: forming device
310: molded article
312: Supply Home
313: Lower end
320: atmosphere partition member
330: cooling roller
335: Cooling unit
350a to 350d:
340: Molding furnace
350: slowly cooled
400: Cutting device

Claims (8)

A method for producing a glass plate,
A melting step of dissolving the glass raw material at least by conduction heating to produce a molten glass containing SnO ₂ as a refining agent,
A defoaming treatment for raising bubbles in the molten glass by defrosting the molten glass by raising the temperature of the molten glass to a temperature higher than or equal to 1630 DEG C at a heating rate of 2.5 deg. C / min or more after the melting process; A bake process including an absorption process in which the bubbles in the molten glass are absorbed into the molten glass;
A molding step of molding the molten glass after the refining step into a plate-shaped glass
&Lt; / RTI &gt; The method according to claim 1,
Wherein the plate-like glass is formed from the molten glass by an overflow down-draw method in the molding step. The method according to claim 1,
The temperature of the molten glass in the refining step may be raised by controlling the current flowing through the metal tube by using at least the metal tube connecting between the melting vessel in which the melting step is performed and the blue sign in which the refining step is performed, Gt; The method according to claim 1 or 3,
Wherein the viscosity of the molten glass at a temperature of 1630 DEG C is 130 to 350 poise. The method according to claim 1 or 3,
Wherein the glass plate has a content of R ' ₂ O of 0 to 2.0 mass% (R' ₂ O is a total of components including Li ₂ O, Na ₂ O and K ₂ O). The method according to claim 1 or 3,
Wherein the glass plate
50 to 70% by mass of SiO ₂ ,
B ₂ O ₃ : 5 to 18% by mass,
Al ₂ O ₃ : 10 to 25% by mass,
MgO: 0 to 10% by mass,
CaO: 0 to 20% by mass,
0 to 20% by mass of SrO,
BaO: 0 to 10% by mass,
And RO: 5 to 20 mass% (wherein R is at least one selected from Mg, Ca, Sr and Ba, and RO is a total of components including MgO, CaO, SrO and BaO). The method according to claim 1 or 3,
And a stirring step of homogenously stirring the components of the molten glass between the refining step and the shaping step,
In the dissolving step, the molten glass is supplied to the refining step at a temperature higher than the temperature at the start of dissolution of the molten glass,
In the refining step, the molten glass is supplied to the stirring step at a temperature lower than the temperature after the absorption treatment,
Wherein in the molding step, the molten glass is supplied at a temperature of log? = 4.3 to 5.7 with respect to the viscosity? (Poise) of the molten glass to be molded into plate glass. delete

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