JP2010111533A - Method of producing glass plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a production method which can suppress generation of bubbles containing SO<SB>2</SB>when producing a glass plate containing a low component ratio of an alkali metal oxide and a relatively high component ratio of SiO<SB>2</SB>using a carbonate. <P>SOLUTION: The production method includes: a melting step of obtaining a molten glass by melting a glass material containing carbonate which has been adjusted in order to obtain a glass containing 57-65 mass% of SiO<SB>2</SB>and at most 2 mass% of an alkali metal oxide; a clearing step of clearing by raising the temperature of the molten glass further; and a molding step of molding the cleared molten glass to a plate. In the melting step, an oxidative gas is bubbled into the molten glass. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention relates to a method for producing a glass plate having a relatively high SiO ₂ content and a low alkali metal oxide content.

Conventionally, when manufacturing a glass plate, nitrates, carbonates, and the like have been used as sources of Group 2 metal oxides such as MgO, CaO, and SrO. For example, when manufacturing a glass substrate for a liquid crystal display, nitrate is selected in order to increase the oxidizability of molten glass. This is because when the oxidizability of the molten glass is lowered, SO ₃ dissolved in the molten glass becomes SO ₂ to generate new bubbles or diffuse into the existing bubbles to grow the bubbles. . In particular, a glass having a composition having a relatively high SiO ₂ content and a low alkali metal oxide content, such as a glass substrate for a liquid crystal display, has a high viscosity in a molten state, and thus bubbles tend to remain.

However, if a large amount of nitrate is contained in the glass raw material, a large amount of nitrogen oxide (NO _x ) is released when the glass raw material is dissolved. Since NO _x causes air pollution, it is required not to exhaust it as much as possible. From such a viewpoint, it is effective to use carbonate instead of nitrate.

However, carbonates that can be used industrially contain more sulfides as impurities than nitrates, so when carbonates are used, the amount of SO _{3 in} the molten glass increases. Moreover, since carbonate has a weaker oxidizing power than nitrate, the oxidizability of molten glass is lower when carbonate is used than when nitrate is used. For this reason, when carbonate is used, bubbles containing SO ₂ are more easily formed in the molten glass than when nitrate is used. The bubbles containing SO ₂ significantly reduce the product yield.

It is known that the addition of a clarifying agent is effective for removing bubbles in the glass plate. However, many refining agents having a high refining effect typified by As ₂ O ₃ have a high environmental load, and removal of bubbles using a large amount thereof may be undesirable from an environmental standpoint.

In addition, Patent Document 1 is not intended to remove bubbles from a glass plate, but to prevent deterioration of transmittance due to reduction of bismuth oxide, but an optical glass containing bismuth oxide is manufactured. In doing so, it is described that oxygen is bubbled into the molten glass. However, this optical glass has a SiO ₂ content of 60 mol% or less (at most, about 20 mass% in terms of conversion), and is easy to melt and clarify.
JP 2005-502574 A

In view of such circumstances, the present invention generates SO ₂ -containing bubbles when producing a glass plate having a relatively high SiO ₂ content and a low alkali metal oxide content using carbonate. It aims at providing the manufacturing method which can suppress this.

To achieve the above object, the present invention provides a carbonate prepared so as to obtain a glass having a SiO ₂ content of 57 to 65 mass% and an alkali metal oxide content of 2 mass% or less. A melting step of obtaining a molten glass by melting a glass raw material, a clarification step of further raising the temperature of the molten glass and clarifying, and a molding step of forming the clarified molten glass into a plate shape, In the melting step, a glass plate manufacturing method is provided, in which an oxidizing gas is bubbled through the molten glass.

According to said structure, the oxidizing property of molten glass when carbonate is used can be improved by bubbling oxidizing gas to molten glass at a melt | dissolution process. Therefore, according to the present invention, the generation of bubbles containing SO ₂ can be suppressed.

  Hereinafter, embodiments for carrying out the present invention will be described in detail. The manufacturing method of the glass plate which concerns on one Embodiment of this invention consists of a melt | dissolution process, a clarification process, a cooling process, and a formation process. Hereinafter, each step will be described.

(Dissolution process)
In the melting step, molten glass is obtained by melting glass raw materials.

The glass raw material is particularly limited as long as it contains carbonate prepared so as to obtain a glass having a SiO ₂ content of 57 to 65% by mass and an alkali metal oxide content of 2% by mass or less. Is not to be done. However, it is preferable that the glass raw material is prepared so as to obtain a glass having substantially the following composition, expressed in mass%.
SiO ₂ 57~65%
Al ₂ O ₃ 15-19%
B ₂ O ₃ 8-13%
MgO 1-3%
CaO 4-7%
SrO 1-4%
BaO 0-2%
Na ₂ O 0-1%
K ₂ O 0-1%
As ₂ O ₃ 0 to 1%
Sb ₂ O ₃ 0 to 1%
SnO ₂ 0-1%
Fe ₂ O ₃ 0 to 1%
ZrO ₂ 0 to 1%

The content of SiO _2, and more preferably 58 to 65 wt%. Here, “substantially” means to allow the presence of a trace component in a range of less than 0.1% by mass. Therefore, the glass having the above composition allows mixing of other trace components in the range of less than 0.1% by mass. Each content of Fe ₂ O ₃ , As ₂ O ₃ , Sb ₂ O _3, and SnO _{2 in} the above composition is such that Fe, As, Sb, or Sn components having a plurality of valences are all Fe ₂ O. ₃ , a value converted by treating as As ₂ O ₃ , Sb ₂ O ₃ or SnO ₂ .

  The carbonate is MgO, CaO, SrO, BaO in the glass composition, and for example, basic magnesium carbonate, calcium carbonate, strontium carbonate, barium carbonate, or the like can be used. That is, the carbonate may be at least one selected from basic magnesium carbonate, calcium carbonate, strontium carbonate, and barium carbonate.

As ₂ O ₃ , Sb ₂ O ₃ , SnO ₂ , and Fe ₂ O ₃ in the glass composition are components having a fining action, and these may be added to the glass raw material as a fining agent.

  In the main melting step, it is preferable that the glass raw material prepared as described above is melted at a set temperature corresponding to the composition and the like to finally obtain a molten glass of 1540 ° C. or higher. More preferably, the temperature of the final molten glass obtained in the melting step is 1545 ° C. or higher.

Further, in the melting step, after the glass raw material is melted and a molten glass is generated, an oxidizing gas is bubbled into the molten glass. By bubbling the oxidizing gas in this manner, the oxidizability of the molten glass can be improved and the generation of bubbles containing SO ₂ can be suppressed. Examples of the oxidizing gas include oxygen, oxygen dioxide, water vapor, etc. Among them, it is most effective to use oxygen. This was confirmed by experiments conducted by the inventors of the present invention.

Although bubbling can be performed at any stage of the melting process after the production of molten glass, the effect of suppressing the generation of bubbles containing SO ₂ can be obtained. It is most effective at an initial stage, that is, immediately after a part of the glass raw material becomes molten glass. The reason for this is considered to be that, since the properties of the glass are determined at the initial stage of melting, if the bubbling is performed at that stage, the oxidizability of the molten glass can be maintained high. In order to realize this, it is preferable to perform bubbling while the temperature of the molten glass changes from 1480 ° C. to 1520 ° C. at least.

Specifically, the bubbling is preferably started when the temperature of the molten glass reaches about 1400 ° C. If the temperature of the molten glass is about 1400 ° C., the viscosity of the molten glass becomes about 10 ^2.5 Pa · s, and bubbling can be performed. Moreover, in order for the molten glass to absorb oxygen, the temperature of the molten glass is This is because the lower one is more effective.

On the other hand, the bubbling may be terminated when the temperature of the molten glass reaches about 1550 ° C. If the temperature of the molten glass is about 1550 ° C., the viscosity of the molten glass is about 10 ^1.5 Pa · s. Preferably, the bubbling is finished before the temperature of the molten glass becomes 3 ° C. (particularly preferably 4 ° C.) lower than the final temperature in the melting step.

  In order to perform the bubbling for the period described above, the bubbling may be started or ended by appropriately determining the state of the molten glass such as the temperature and viscosity in the continuous melting step.

(Clarification process)
In the clarification step, the molten glass is further heated to clarify. This clarification is preferably performed by raising the temperature of the molten glass to 1600 ° C. or higher, more preferably 1610 ° C. or higher.

(Cooling process)
In the cooling step, the clarified molten glass is cooled to a temperature suitable for molding (for example, 1200 ° C.). This cooling is performed, for example, while guiding molten glass through a conduit made of platinum.

(Molding process)
In the forming step, the molten glass cooled after clarification is formed into a plate shape. Examples of a method for forming a molten glass into a plate shape include a float method, but the present invention is particularly suitable for a method for forming a molten glass into a plate shape by a downdraw method.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not restrict | limited to these Examples at all.

Example 1
First, the glass raw material containing carbonate was displayed by mass%, and it prepared so that the glass which consists of the following compositions could be obtained.
SiO ₂ 60.9%
Al ₂ O ₃ 16.9%
B ₂ O ₃ 11.6%
MgO 1.7%
CaO 5.1%
SrO 2.6%
BaO 0.7%
K ₂ O 0.25%
SnO ₂ 0.13%
Fe ₂ O ₃ 0.15%

  As the carbonate, basic magnesium carbonate, calcium carbonate, strontium carbonate and barium carbonate were used, and the whole amount of MgO, CaO, SrO and BaO in the above composition was supplied as carbonate.

  100 g of the prepared glass raw material was put in a platinum crucible and stored in a magnetic container with a lid. After that, a bubbling tube (platinum) is attached to the lid of the porcelain container so that oxygen can be supplied into the glass raw material in the platinum crucible, and a thermocouple for measuring the temperature of the glass raw material or molten glass (platinum) Alloy) was attached and the magnetic container was put into an electric furnace. The bubbling tube and the tip of the thermocouple were led out of the electric furnace, and an oxygen cylinder and a thermometer (EC5500 manufactured by Okura Electric Co., Ltd.) were attached to the tip of each.

  In that state, first, as a melting step, the electric furnace was set at 1550 ° C. and heated for 2 hours. Further, oxygen was bubbled into the molten glass during the melting process. Bubbling started 30 minutes after the start of heating, continued for 30 minutes, and ended after 1 hour from the start of heating. The flow rate of bubbling was 0.75 L / min (1 atm, 20 ° C.).

  Two hours after the start of heating (after the completion of the melting step), as the clarification step, the temperature setting of the electric furnace was changed to 1620 ° C., and the temperature of the molten glass was further increased to perform clarification for 2 hours.

  After 4 hours from the start of heating (after the clarification process), as the cooling process, the set temperature of the electric furnace was lowered to 1200 ° C. at a constant rate over 3 hours to cool the molten glass.

  Here, when the set temperature of the electric furnace from the melting step to the cooling step is shown in a graph, it becomes like a solid line in FIG. In these steps, the temperature of the glass raw material or molten glass was measured in a timely manner with the thermometer described above. The results are shown in Table 1. When this is shown in the graph, it becomes like the one-dot chain line in FIG.

  From Table 1, it can be seen that the temperature of the molten glass at the start of bubbling was 1463 ° C., and the temperature of the molten glass at the end of bubbling was 1542 ° C. In addition, the temperature of the final molten glass obtained in the melting step is 1548 ° C., and it can be seen that the temperature of the molten glass was 6 ° C. lower than the final temperature of 1548 ° C. when the bubbling was completed.

  After 7 hours from the start of heating (after the cooling step), as a forming step, the platinum crucible was transferred to another electric furnace set at 720 ° C. and allowed to stand for 1 hour.

  After 8 hours from the start of heating, the electric furnace was turned off, the glass was cooled to room temperature, and then a platinum crucible was taken out of the electric furnace to obtain a glass sample.

(Example 2)
A glass sample was obtained in the same manner as in Example 1 except that oxygen bubbling started 1.5 hours after the start of heating and ended after 2 hours.

(Comparative example)
A glass sample was obtained in the same manner as in Example 1 except that oxygen was not bubbled.

(test)
For the glass samples of Examples 1 and 2 and the comparative example, the number of bubbles generated in the glass sample was measured, and the number of bubbles per 1 g was calculated. Further, measured using a mass spectrometer (an In Process Instruments Inc. GIA522type) component of the bubbles was calculated the ratio of SO ₂ contained in the bubbles mol%. These results are shown in Table 2.

From Table 2, it can be seen that in Examples 1 and 2 in which bubbling was performed, the number of bubbles was much smaller than in the comparative example in which bubbling was not performed. Further, it can be seen that in Example 1 in which bubbling was performed at the initial stage of dissolution, the ratio of SO _{2 in} the bubbles was smaller than in Example 2 in which bubbling was performed at the end of the dissolution process. This is presumed to be a result of suppressing the reaction of SO ₃ → SO _{2 in} the molten glass.

Furthermore, the transmittance | permeability of the electromagnetic waves with a wavelength of 200-500 nm was measured about each glass sample. The result was as shown in FIG. From this graph, it can be seen that the transmittance in Examples 1 and 2 is greatly reduced from 270 nm to 400 nm than in the comparative example. The reason for this is considered to be that the proportion of Fe ₂ O ₃ in the coexistence state of FeO and Fe ₂ O ₃ is larger in Examples 1 and 2 than in the comparative example. From this, it can be seen that in Examples 1 and 2, the oxidizability of the molten glass was higher than in the comparative example. In FIG. 2, although Example 1 and Example 2 seem to be on the same line, the transmittance of Example 1 was actually slightly smaller than that of Example 2. From this, it can be seen that the oxidizability of the molten glass was higher in Example 1 than in Example 2.

(Example of glass plate)
A glass raw material containing a carbonate prepared so as to have the composition shown in Example 1 is used with a continuous melting apparatus equipped with a melting tank made of refractory bricks and an adjustment tank made of platinum (a tank for performing a clarification process). The molten glass is melted at a set temperature of 1550 ° C. to obtain a molten glass of about 1550 ° C., this molten glass is clarified at 1620 ° C. and stirred at 1550 ° C. Molded to obtain a glass plate. In the melting tank, oxygen was bubbled at a position where the temperature of the molten glass was about 1460 to 1540 ° C.

When the number of bubbles was measured for the glass plate thus obtained by the same method as in Examples 1 and 2 and the comparative example, the number of bubbles was as very small as 22 × 10 ⁻⁶ / cm ³ . Thus, when a glass plate is manufactured by applying the present invention, a high-quality glass plate is obtained, and such a glass plate is a large flat plate of 1870 × 2200 mm size or more called the seventh generation. It is suitable for use in a glass substrate of a panel display.

The present invention is particularly useful as a method for producing a glass plate having a relatively high SiO ₂ content and a low alkali metal oxide content, which is used for glass substrates of flat panel displays such as liquid crystal displays and plasma displays. It is.

It is a graph which shows the relationship between the elapsed time from a heating start, the preset temperature of an electric furnace, and the temperature of a molten glass. It is a graph which shows the electromagnetic wave transmittance measurement result with respect to the glass sample of Examples 1, 2 and a comparative example.

Claims (10)

A molten glass is obtained by melting a glass raw material containing carbonate prepared so as to obtain a glass having a SiO ₂ content of 57 to 65% by mass and an alkali metal oxide content of 2% by mass or less. A dissolution process;
A clarification step of further raising the temperature of the molten glass to clarify,
Forming the clarified molten glass into a plate shape, and
In the melting step, an oxidizing gas is bubbled through the molten glass.   The method for producing a glass plate according to claim 1, wherein in the melting step, the glass raw material is melted to finally obtain a molten glass of 1540 ° C. or higher.   The manufacturing method of the glass plate of Claim 2 which performs the said bubbling while the temperature of the said molten glass changes from 1480 degreeC to 1520 degreeC at least.   The manufacturing method of the glass plate of Claim 3 which complete | finishes the said bubbling before the temperature of the said molten glass becomes temperature lower 3 degreeC than the final temperature in the said melt | dissolution process. The said glass raw material is represented by the mass%, and the glass plate manufacture as described in any one of Claims 1-4 prepared so that the glass which consists of the following compositions substantially may be obtained. Method.
SiO ₂ 57~65%
Al ₂ O ₃ 15-19%
B ₂ O ₃ 8-13%
MgO 1-3%
CaO 4-7%
SrO 1-4%
BaO 0-2%
Na ₂ O 0-1%
K ₂ O 0-1%
As ₂ O ₃ 0 to 1%
Sb ₂ O ₃ 0 to 1%
SnO ₂ 0-1%
Fe ₂ O ₃ 0 to 1%
ZrO ₂ 0 to 1%   The said carbonate is a manufacturing method of the glass plate of Claim 5 which is at least 1 type chosen from basic magnesium carbonate, calcium carbonate, strontium carbonate, and barium carbonate.   The said oxidizing gas is a manufacturing method of the glass plate as described in any one of Claims 1-6 which is oxygen.   In the said formation process, the said molten glass is shape | molded in plate shape by the down draw method, The manufacturing method of the glass plate as described in any one of Claims 1-7.   In the said clarification process, the temperature of the said molten glass is raised to 1600 degreeC or more, and the manufacturing method of the glass plate as described in any one of Claims 1-8 which performs clarification.   The said glass plate is a manufacturing method of the glass plate as described in any one of Claims 1-9 for the glass substrate of a flat panel display.

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