TW201204664A - Vacuum degassing method for molten glass - Google Patents

Abstract

The disclosed vacuum degassing method for alkali-free glass can apply optimal vacuum degassing conditions to a plurality of types of alkali-free glass having different viscosities. In said method, molten glass is vacuum-degassed as follows: molten glass is poured into a vacuum degassing tank, the interior of which is kept in a vacuum state. The disclosed method is characterized in that the molten glass is alkali-free glass and the vacuum degassing is carried out under the condition that the viscosity η (Pas) and SO3 concentration [SO3] (ppm) of the molten glass passing through the vacuum degassing tank fulfill formula (1). (1)18.2 + 1003/η - 1.05[SO3] ≥ 8.

Description

201204664 VI. Description of the invention: Field of the invention of the invention 1 FIELD OF THE INVENTION The present invention relates to a vacuum degassing method for molten glass. BACKGROUND OF THE INVENTION In order to improve the quality of a formed glass product, a clear step is used before the molten π glass which has been melted in the melting furnace is formed by a forming device. In the molten glass, it is known that, in addition to the known clearing step, a clearing agent is added to the raw material in advance, and the molten glass obtained by melting the raw material is stored and maintained at a predetermined temperature, thereby melting with a clearing agent. The method in which bubbles in the glass grow and float. Further, a method of degassing under reduced pressure is known, in which a molten glass is introduced into a reduced pressure environment and bubbles in a molten glass fluid which is connected to a (four) moving force are greatly grown in a molten glass. The contained air bubbles are stained and broken by foaming, and then discharged from a reduced pressure environment. In order to efficiently remove the bubbles from the smelting glass, it is preferred to carry out the vacuum degassing method by combining the above two methods, that is, using a molten glass to which a clearing agent is added. As a clearing agent for glass, there are an oxide-based π-etching agent such as As2〇3, Sb2〇3, and Sn02, a vapor-based clearing agent such as NaC1^ metal, s〇3, etc., and As2〇3 And Sb2〇3, especially the operation, because of the heavy environmental load, it is required to suppress its use. In addition, the temperature at which the Sn(R) 2 emits oxygen is high at 15 〇〇t: or higher, and it is difficult to effectively use the liquid as a clearing agent. Further, when a metal oxide is added in an amount sufficient for clarity, the alkali-free glass contains an alkali metal, so that it is an unusable clearing agent. Therefore, as a clearing agent for alkali-free glass, s〇3 is used. Since s〇3 also has an effect of improving the initial solubility of the input raw material, it is satisfactory as a clearing agent. Although the pressure and temperature conditions in the vacuum degassing tank at the time of performing vacuum degassing are shown in Patent Documents 1, 2, etc., even if the same type of glass is broken, specifically, the same alkali-free glass has different compositions. In the case where the viscosity characteristics are different, the clear effect of defoaming under reduced pressure is different, and there is a case where a desired clear effect cannot be obtained. When the molten glass is melted in the melting tank to obtain molten glass, it is necessary to adjust the glass melting temperature in accordance with the viscosity of the glass, and the temperature of the molten glass supplied from the melting tank to the vacuum degassing tank varies depending on the viscosity characteristics of the glass. . As a result, even if the pressure and temperature conditions in the vacuum degassing tank are excellent in clearing effect on a certain viscous glass, it is impossible to obtain a glass having a different composition and a relationship between temperature and viscosity. The situation of the clear effect. Patent Document 3 describes a case where the glass-based lime-lime glass is produced, and the pressure in the vacuum degassing vessel is lowered to a ratio of a ratio of a -OH value, a SO3 content of the glass, and a molten glass temperature. The derived bubble growth start pressure is low, and it is possible to produce the glass without the use of a clearing agent so that the glass of 201204664 does not remain after the production, but it is considered that even if the method of Patent Document 3 is applied to the composition completely different from the soda lime glass. Alkali glass does not exert the desired clear effect. Specifically, it is considered that the solubility of the alkali-free glass system S03 is extremely small as compared with the limestone glass, and the effect on the clearing effect is small, and the method of Patent Document 3 cannot be applied. Prior Technical Literature Patent Literature

[Patent Document 1] International Publication No. WO2008/029649 [Patent Document 2] International Publication No. WO2008/093580 (Patent Document 3) International Publication No. WO2007/111079 (Kentin J Summary of Invention) In view of the problems of the prior art, the present invention provides a vacuum degassing method for an alkali-free glass capable of imparting optimum decompression defoaming conditions to a plurality of alkali-free glasses having different viscous properties. Means for Solving the Problems In order to achieve the above object, the present invention provides a vacuum degassing method for molten glass by flowing a molten glass into a vacuum degassing vessel which has been maintained in a reduced pressure state. A method for vacuum defoaming of molten glass, characterized in that the molten glass is an alkali-free glass, and the method is a viscosity π (Pa · S) of the molten glass when the degassing tank is passed through a vacuum, and the molten glass The S〇3 concentration [S03] (ppm) satisfies the condition of the following formula (1) to carry out vacuum degassing: 18.2 + 1〇〇3/η-l.〇5x[S〇3] ^ 8 -(1) - (1) 201204664 In the above-described vacuum degassing method for molten glass, it is preferable that the S03 concentration [S03] (ppm) satisfies the following formula (2): [S03] = -0.0775xTmax + 135.02 (2) (In the above formula, Tmax is the highest temperature fc of the molten glass in the melting tank)). Further, in the vacuum degassing method for the molten glass, when the viscosity of the molten glass is 1 〇 2d Pa · s, the temperature is T2 (°c), and the Tmax is satisfied to satisfy T2-120 ° C to T 2 . -10 ° C is preferred. Further, in the vacuum degassing method for the molten glass, the S〇3 concentration [S03] (ppm) of the molten glass is preferably 3 to 40 ppm. Further, in the vacuum degassing method for the molten glass, the maximum temperature (°C) of the molten glass in the melting tank, that is, Tmax is preferably 1400 to 1700 t. Further, in the alkali-free glass of the above-described vacuum defoaming method of molten glass, it is preferable to contain the following components (in terms of % by mass):

Si02 : 50~66% ;

Al2〇3 : 10.5-22% ; B2〇3 : 0~12% ;

MgO : 0~8% ;

CaO : 0~14.5% ;

SrO : 0~24% ;

BaO : 0~13.5% ; 201204664

MgO+CaO+SrO+BaO : 9 to 29.5%. The above-mentioned "~" of the numerical range is used to mean that the numerical values described before and after are set to the lower limit and the upper limit, and the "~" in the following description has the same meaning and is used. EFFECT OF THE INVENTION According to the vacuum degassing method of the present invention, it is possible to impart optimum decompression defoaming conditions to a plurality of alkali-free glasses having different viscous properties. As a result, the number of bubbles in the molten glass after the vacuum degassing treatment is extremely small, and it is possible to produce a glass having a high function and high quality with few bubbles. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a cross-sectional view showing a configuration example of a vacuum degassing apparatus using the vacuum degassing method of the present invention. Fig. 2 is a graph in which the relationship between Tmax and [S03] is plotted. Fig. 3 is a graph in which the relationship between the calculated value of the formula (a) and the number of bubbles (bubble density) in the glass plate is plotted. [Embodiment 3] Mode for carrying out the invention Hereinafter, the vacuum degassing method of the present invention will be described in more detail using a drawing. Fig. 1 is a cross-sectional view showing a configuration example of a vacuum degassing apparatus used in the vacuum degassing method of the present invention. In the vacuum degassing apparatus 1 shown in Fig. 1, the cylindrical decompression degassing tank 12 is housed and disposed in the decompression chamber 11 so that the long axis is aligned in the horizontal direction. Below the end of the vacuum degassing tank 12, a riser 13 that is aligned in the vertical direction is attached, and a downcomer 14 is attached to the lower end of the other end. A part of the riser 13 and the downcomer 14 is 201204664 in the decompression chamber 11. The riser 13 is connected to the vacuum degassing tank 2 to guide the molten glass crucible from the refining tank 20 to the vacuum degassing tank 12. The descending system is connected to the vacuum degassing tank 12, and the molten glass G which has been defoamed under reduced pressure is led to the next processing tank (not shown). In the decompression chamber, the heat insulating material 15 such as the heat insulating sheet for the heat insulating coating is placed in the vacuum degassing tank 12, the riser 3, and the lowering pipe 14. The vacuum degassing tank 12 is decompressed by a suction suction hole (not shown) which is placed in the decompression chamber 11 through a vacuum suction device (not shown). In the vacuum degassing apparatus 第 shown in Fig. 1, the vacuum degassing tank 12, the riser pipe 13, and the down pipe 14 are pipes for melting glass, and a material excellent in heat resistance and corrosion resistance to molten glass is used. Manufacturing. As an example, it is made of platinum, a platinum alloy, or a reinforced platinum obtained by dispersing a metal oxide in platinum or a platinum alloy. Further, it may be made of a ceramic non-metallic inorganic material, that is, a dense refractory. Further, it may be a case where platinum or a platinum alloy is embedded in a dense refractory. In the vacuum degassing method of the present invention, the molten glass G supplied from the melting tank 2 is passed through a vacuum degassing tank 12 which has been depressurized to a predetermined degree of pressure reduction to perform vacuum degassing. The molten glass G is preferably supplied to the vacuum degassing tank 12 continuously and discharged. Further, in terms of productivity, the flow rate of the molten glass is preferably 2 to 100 tons/day. The molten glass G based on the vacuum degassing method of the present invention is an alkali-free glass and SO3 is added as a clearing agent. The amount of addition of SO3 is 0.1 to 0.45 parts by mass based on 100 parts by mass of the raw material of the glass mother material (hereinafter referred to as "parts by mass", which means 201204664 Μ with respect to 100 parts by mass of the raw material of the glass mother composition. Add amount) is better. When the amount of the super fox is used, if the amount of the foam layer in the melting tank is excessive and less than 0.1 part by mass, there is a possibility that the clear effect is insufficient. The amount of S〇3 added is preferably 〇_2 to 〇4 parts by mass. The S〇3 is added to the glass mother composition raw material, for example, in the form of a compound such as CaS〇4, MgS〇4, SrS〇4, or BaS〇4. S 03 added as a clearing agent is represented by the following formula in 16 molten glass, and is decomposed into so2 and 〇2. S〇3 -> S〇2 + l/2〇2 In order to homogenize the molten glass, the temperature of the molten glass in the melting tank is kept at a high temperature. Therefore, in the rotary groove, a part of the transfer is volatilized. The inventors of the present invention found that the production amount of the molten glass is 2 to 1 〇 (the W-day scale refining tank, when the amount of the s〇3 added is 〇~〇45 Berry, the flow from the melting tank Between the s〇3 concentration [S〇3] (ppm) in the molten glass and the highest temperature T_^c) of the molten glass in the melting tank, the straight line having the second towel, that is, the following formula (2) ) the relationship shown. [S03] = -〇.〇775xTmax + 135.02 (2) In addition, since the temperature of the molten glass after flowing out of the melting tank is low in the melting tank, the S〇2 system hardly volatilizes and can be maintained and maintained. The concentration of s〇3 in the molten glass at the point of melting of the melting tank is approximately the same. Therefore, the concentration of 8 〇 3 of the molten glass when the degassing vessel is depressurized can be maintained at substantially the same level as the concentration of s 〇 3 in the molten glass at the point of exiting from the melting tank. The maximum temperature Tmaxfc) of the molten glass is the southernmost temperature of the molten glass in the glass melting tank. Although it is different from the composition and size of the 201204664 melting tank used, it is based on molten glass. In the viewpoint of homogenization, when the temperature of the molten glass is set to be 102 dPa*s, the temperature is set to T2fC) to satisfy the distillation of 2-120. (:~T2-l〇t: preferably, preferably din 2_1 〇〇 it ~ t2-30 ° C, more preferably T2-90 ° C ~ T2-50 ° C way to set. Also, smelting glass When the maximum south temperature Tmax is too high, the intrusion of the furnace material rapidly causes the life of the dissolution tank to be shortened. On the other hand, when the maximum temperature Tmax of the molten glass is too low, the removal of bubbles is suppressed. The reason is that the maximum temperature Tmax of the molten glass is preferably μοο'ποο^. The concentration of S〇3 in the molten glass flowing out of the melting tank [S〇3] (that is, in the melting tank, the molten glass flows from upstream to downstream) The concentration of SO3 in the molten glass in the downstream region of the dissolution tank which has been homogenized is representatively the concentration of §3 in the glazing glass in the melting tank 2〇 in the lower portion of the riser 13 of Fig. 1 [S〇3] It is expressed by mass% in the range of 3 to 4 〇 ppm, because it is excellent in clearing effect, and it is good in car smashing. SO in molten glass; when the concentration is less than 3 ppm, the clearing action in the pressure reducing tank is insufficient. When the concentration of s〇3 in the middle exceeds 4 paws, the molten glass is reboiled at the time of manufacture, so that it is manufactured. In the glass, the SO3 concentration in the smelting glass is preferably from 3 to 30 ppm, more preferably from 3 to 20 ppm. The inventors of the present invention use the viscosity and the amount of S03 added as a clearing agent. The vacuum defoaming treatment of the molten glass was carried out without using the glass, and the number of defects in the glass plate formed by molding the molten glass after the vacuum degassing treatment was measured (hereinafter, the bubbles in the r glass plate are also referred to as abbreviations). As a result of the number, it was found that the viscosity of the molten glass at the time of passing through the degassing vessel was 77 (Pa · S) 10 201204664 and the S03 concentration [S〇 3] (ppm) of the molten glass and the glass plate The number of bubbles has a relationship with each other. Here, the number of bubbles in the glass plate is measured because it is difficult to measure the number of remaining bubbles in the molten glass after the vacuum degassing treatment. The number of bubbles of the molten glass after that can be seen as almost no change. Therefore, the measurement result of the number of bubbles in the glass plate is substantially the same as the number of bubbles remaining in the molten glass after the decompression treatment. So, very clearly The viscosity β (Pa. s) of the molten glass when the degassing vessel is depressurized by pressure and the SO3 concentration [S〇3] (ppm) of the molten glass and the bubbles remaining in the molten glass after the vacuum degassing treatment The inventors also have a relationship based on the knowledge of δ Xuan and concentrate on the research, and found that the viscosity of the molten glass ^ (Pa · s) and the SO of the glazed glass when degassing the tank by vacuum; When the concentration [S〇3] (ppm) is the condition of the following formula (丨), when the vacuum degassing is performed, the number of bubbles remaining in the molten glass after the vacuum degassing treatment can be greatly reduced. High-quality, high-quality glass with few bubbles can be obtained. 18.2 + 1003/η-1.05x[SO3] ^ 8 Fig. 3 is the left side of the above formula (1) when the conditions of the viscosity β and the SO3 concentration are variously changed (hereinafter, in the present specification, it is called "form (a) ))) A graph drawn from the relationship between the number of bubbles (bubble density) in a glass plate (sample). Further, the degree of decompression of each data in Fig. 3 is a pressure at which the number of bubbles in the sample is the smallest. In Fig. 3, it is shown that the number of bubbles in the glass plate 201204664 can be greatly reduced when the above formula (1) is satisfied. Further, the curve in the figure is obtained by approximating the average value of the horizontal interval of the horizontal axis by the third-order polynomial. The number of bubbles in the glass plate is also different depending on the application of the glass plate to be produced. In the case of the liquid crystal display substrate, it is preferably 〇25/kg or less, and preferably 0.2/kg or less. It is better to use 〇15/kg or less. Here, the concentration of S〇3 in the molten glass when passing through the vacuum degassing tank is maintained to be substantially the same as the concentration of S〇3 in the molten glass flowing out from the melting tank as described above, and because of the melting tank Between the s〇3 concentration [s〇3] (Ppm) in the molten glass and the highest temperature Tmax fc of the molten glass in the melting tank, there is a correlation as expressed by the above formula, so The concentration of s〇3 in the molten glass at the time of the defoaming tank can be determined by the maximum temperature of the molten glass in the melting tank. On the other hand, the viscosity D (Pa · s) of the molten glass when the degassing vessel is depressurized is determined by the viscosity characteristics of the glass and the temperature of the molten glass at the time of decompression degassing. Therefore, the vacuum defoaming can be carried out by the viscosity of the molten glass when the degassing vessel is reduced in pressure and the SO3 concentration of the molten glass satisfies the condition of the above formula (1), and any of the following procedures can be carried out. (a) The viscosity of the molten glass when passing through the vacuum degassing tank is adjusted by adjusting the temperature of the molten glass when the degassing vessel is depressurized according to the viscosity characteristics of the glass. (b) Adjusting the concentration of s〇3 12 201204664 in the glazing glass by the degassing defoaming tank by adjusting the maximum temperature Tmax (C) ' of the molten glass in the melting tank according to the formula (2). (C) Implement both (a) and (9) above. In the vacuum degassing method of the present invention, the temperature of the molten glass when passing through the vacuum degassing vessel is adjusted by the viscosity characteristic of the glass, and the vacuum degassing can be performed by satisfying the conditions of the above formula (1). It is easy to set optimal decompression defoaming conditions for different viscous glasses. However, the temperature of the molten glass when the degassing vessel is depressurized by pressure is maintained at 13 〇〇 to 1600, for the reason of maintaining the durability of the structural material forming the vacuum degassing vessel and suppressing the disadvantages of the structure. . The range of (: is preferably in the range of 1350 to 1550 ° C, preferably in the range of 1370 to 1500. The range of (:: is more preferable.) In the vacuum degassing method of the present invention, the formula (1) The left side (formula (a)) is preferably 9 or more, more preferably 10 or more. In the vacuum degassing method of the present invention, the pressure reduction degree of the vacuum degassing tank is maintained at 100 mmHg (13_3 kPa) to 400 mmHg. (53.3 kPa) is preferable, and it is more preferable to maintain 150 mmHg (20 kPa) to 300 mmHg (40 kPa). In the present specification, the term "decompression degree in the degassing defoaming tank means the pressure degree of the atmospheric pressure reference. That is, the pressure difference between the absolute pressure in the vacuum degassing tank and the atmospheric pressure. The degree of pressure reduction in the vacuum degassing tank can be controlled by adjusting the gauge pressure of a vacuum decompression means such as a vacuum pump. The alkali-free glass used in the vacuum degassing method is preferably expressed by mass% of the following oxides, and is preferably glass containing the following components: Si02: 50 to 66%;

Al2〇3 : 10.5~22% ; 13 201204664 B2〇3 : 0~12% ;

Mg〇 : 〇~8% ;

CaO : 〇 ~ 14.5% ;

SrO : 〇~24% ;

BaO : 〇 ~ 13.5% ;

MgO+CaO+SrO+BaO : 9 to 29.5%. Further, the alkali-free glass having the above components is a composition of a glass plate produced by the above-described vacuum degassing method. The composition of the molten glass in the scattering tank in the lower portion of the riser pipe and the composition of the glass plate produced by the defoaming treatment by the vacuum degassing vessel are considered to be practically not changed. The concentration of S03 in the molten glass is also the same as the concentration of S〇3 in the glass plate.

When Si〇2 exceeds 66%, the meltability of the glass is lowered, and it is easy to devitrify. At 64°/. The following is better, preferably less than 62%. When it is less than 50%, the specific gravity increases, the strain point decreases, the thermal expansion coefficient increases, and the chemical resistance decreases. More preferably, 56% or more, and more preferably 58% or more.

It is necessary that the Al2〇3 system suppresses the phase separation of the glass and increases the composition of the strain point. When it exceeds 22%, devitrification is likely to occur and chemical resistance is low. It is preferably 21% or less, and more preferably 18% or less. When it is less than 1〇5%, the glass is easily separated, and the strain point is low. It is preferably 12% or more, and more preferably 15% or more. & 〇 3 is not necessary, it is a component which lowers the specific gravity and improves the meltability of the glass, making it less susceptible to devitrification. When the pressure exceeds 22%, the strain point is low, the resistance is low, or the volatilization becomes remarkable when the glass is melted, resulting in an increase in the inhomogeneity of the glass. ΐ·χΐ 2% or less is better, and 9% or less is more preferable. When less than 1%,

14 201204664 When the specific gravity increases and the melting property of the glass is low, it is easy to devitrify, preferably 2% or more, more preferably 4% or more, and even more preferably 6% or more. Further, MgO is not essential, and it is a component which lowers the specific gravity and improves the martenability of the glass. When it exceeds 8%, the glass becomes easily phase-separated, or easily devitrified, or has low chemical resistance. It is preferably 6% or less, and more preferably 5% or less. When MgO is contained, it is preferably 1% or more. In particular, in order to maintain the refining property and at the same time reduce the specific gravity, it is preferable to contain 3% or more.

CaO is not necessary', but it can contain up to 14.5% because it can improve the devitrification of the glass and make it less susceptible to devitrification. When the ratio exceeds 14_5 〇 / 〇, the specific gravity increases and the coefficient of thermal expansion becomes large, but it is easily devitrified. It is preferably 9% or less, and more preferably 7% or less. When CaO is contained, it is preferably 2% or more, more preferably 3 % or more.

SrO is necessary to inhibit the phase separation of the glass and is not easily devitrified. More than 24°/. When the specific gravity increases and the coefficient of thermal expansion becomes large, it is easily devitrified. It is preferably 12.5% or less, and more preferably 8.5% or less. Since BaO suppresses the phase separation of the glass and makes it less susceptible to devitrification, it can be contained up to 13.5%. When the ratio exceeds 13.51⁄4, the specific gravity increases and the coefficient of thermal expansion becomes large. It is preferably 2% or less, preferably 1% or less, and more preferably 1% or less. In particular, when it is important to reduce the weight of the glass substrate, it is preferably not contained. The total amount of the above MgO, CaO, SrO, and BaO is preferably in the range of 9 to 29.9%, that is, ^^^<^0+81>0+3&0. When the total amount exceeds 29_9%, the specific gravity increases, which is not preferable. Further, when the total amount is less than 9%, the solubility is poor, which is not preferable. The components of the composition of the alkali-free glass of the preferred embodiment of the present invention may be as described above, and may contain 5% or less of the above-mentioned 15 201204664 minutes, for example, Zr〇2 or the like.

The As2 03 and Sb2 03 are not indispensable except that they are inevitably mixed as impurities, that is, they are not substantially contained. In the vacuum degassing method of the present invention, a clearing agent other than S03 may be used in combination. In this case, specific examples of the other clearing agent that can be used in combination include a fluorine compound, a gas compound, and Sn02. These other clearing agents can be contained in an alkali-free glass in an amount of 2% by mass or less, preferably 1% by mass or less, more preferably 0.5% by mass or less. The influence of the other clearing agent other than S03 on the formula (1) was confirmed to have substantially no effect according to another experiment by the inventors of the present invention. The dimensions of each component of the vacuum degassing apparatus used in the vacuum degassing method of the present invention can be appropriately selected as necessary. The size of the degassing defoaming tank is not limited to whether the vacuum degassing tank is made of platinum or a platinum alloy or a dense refractory material, and can be appropriately selected according to the vacuum degassing apparatus to be used. The specific example of the size of the vacuum degassing tank 12 shown in Fig. 1 is as follows. • Length in the horizontal direction: 1 to 20 m • Inner diameter: 0.2 to 3 m (circular cross section) The vacuum degassing tank 12 is made of platinum or platinum alloy, and the thickness is preferably 0.5 to 4 mm. The decompression chamber 11 is made of metal, for example, stainless steel, and has a shape and size capable of accommodating the decompression defoaming groove 12. The riser pipe 13 and the downcomer pipe 14 are made of platinum or a platinum alloy or a compact refractory material, and can be selected according to the vacuum degassing apparatus to be used. For example, the sizes of the riser 13 and the downcomer 14 can be configured as follows. • Inner diameter: 0.05 to 0.8 m • Length: 0.2 to 6 m When the riser 13 and the downcomer 14 are made of platinum or a platinum alloy, the thickness is preferably 0.4 to 5 mm. EXAMPLES Hereinafter, the present invention will be more specifically described based on examples. However, the present invention is not limited by this. (Example 1) In this example, vacuum defoaming of molten glass was carried out using an alkali-free glass A having the following composition. The composition of the alkali-free glass A is SiO 2 : 59.8%, Al 2 〇 3 : 17.20 / 〇, B 2 〇 3 : 7.8%, Mg 〇: 3.3%, CaO: 4.1%, SrO: 7.7%,

BaO: 0·1°/〇 ‘The viscosity of the molten glass is 1〇2dPa·s. The temperature is 2, 1657 C. The composition of the glass A is the composition of the glass plate to be produced. SO3 as a clearing agent is added to the raw material of the glass master which has been prepared to have the above composition, and the resultant is put into a melting tank to be melted to obtain a molten glass. Further, SO3 was added in an amount of 0.3 part by mass based on 1 part by mass of the raw material of the glass mother composition. The melting tank was produced in a molten glass having a capacity of 20 ton/day. The maximum temperature Tmax (°C) of the molten glass in the melting tank was 1574 °C. From this value and the above formula (2), the S〇3 concentration [S〇3] system ΐ3·〇ρριη in the molten glass flowing out from the melting tank can be estimated. The molten glass obtained in accordance with the above procedure was degassed under reduced pressure by a vacuum degassing vessel having a degree of internal pressure reduction of 21.3 kPa. The vacuum degassing tank pass 17 201204664 The temperature of the molten glass which is obsolete is 142 (rc, and the viscosity of the molten glass when the degassing degassing tank passes 7? is 117 Pa. s. From the results, the left side of the above formula (1) The calculated value of the formula is Π.1. For the glass plate obtained by molding the molten glass after the vacuum degassing treatment, when the number of bubbles in the glass plate is measured, it is on/kge (Comparative Example 1-1). The temperature of the molten glass when the vacuum degassing tank was passed was 1330 C, and the viscosity of the molten glass when the vacuum degassing tank passed was set to 400 Pa·s. The same procedure as in Example 实施 was carried out. The calculated value of the formula (a) on the left side of the formula (1) is 7.1. The glass plate obtained by molding the molten glass after the vacuum degassing treatment is 0 2 qg/kg when the number of bubbles in the glass plate is measured. (Comparative Example 1-2) The same procedure as in Example 实施 was carried out except that the maximum temperature Tmax (〇c) of the molten glass in the melting tank was set to wstc. From this value and the above formula (2) 'predicted from melting The concentration of s〇3 [s〇3] in the molten glass from which the trough flows out is 2 〇.〇ppm. The calculated value of the above formula (a) is 5.8. When the number of the bubbles in the glass plate was measured, the number of the bubbles in the glass plate was 0.39 pieces/kg. (Example 2) This example uses an alkali-free glass B of the following composition. The defoaming of the molten glass was carried out under reduced pressure. The composition of the alkali-free glass B was si〇2: 59.5%, 丨2〇3: ΐ7·3%> Β2〇3: 8.1% 'MgO: 4.7%> CaO: 5.9% ' SrO : 4.5% '

18 201204664

BaO : 0°/. ' The viscosity of the molten glass is 1 〇 2dpa · s. The temperature is 2, 1611 °C. The composition of the alkali-free glass B is similarly the composition of the glass plate to be produced. S〇3, which is a clearing agent, is added to the raw material of the glass master which has been prepared to have the above composition, and the resultant is put into a melting tank to be melted to obtain molten glass. In addition, S〇3 is added in an amount of 0.3 parts by mass based on 100 parts by mass of the raw material of the glass mother composition. The same melting tank as in Example 1 was used, and the temperature Tmax of the molten glass in the melting tank was set to 1523 ° C. From this value and the above formula (2), the molten glass flowing out from the melting tank can be estimated. The concentration of s〇3 in the middle [s〇3] is 17 ppm. The molten glass obtained according to the above procedure is defoamed under reduced pressure by a vacuum degassing vessel having an internal pressure reduction of 21.3 kPa. The temperature of the molten glass at the time of the passage of the groove was 14 〇〇. (: The viscosity of the molten glass when the vacuum degassing tank passed was 7/91 Pa·s. From the results, the left side of the above formula (1) ( The calculated value of a) is n 4. When the number of the bubbles in the glass plate is measured for the glass plate obtained by molding the molten glass after the vacuum degassing treatment, it is 12 pieces/kg 〇 (Comparative Example 2-1) The temperature of the molten glass when the vacuum degassing tank was passed was set to 135 Torr. (The viscosity of the molten glass when the vacuum degassing tank passed was set to 176 Pa·s, and the same procedure as in Example 丨 was carried out. Procedure: The calculated value of the formula (a) on the left side of the above formula (1) is 6. Forming the molten glass after defoaming under reduced pressure Glass plate, 19 201204664 When the number of bubbles in the glass plate was measured, it was 0.36 / kg. (Comparative Example 2-2) The maximum temperature Tmax (°C) of the molten glass in the melting tank was set to 1457°. In addition to C, the same procedure as in Example 1 was carried out. From this value and the above formula (2), it was estimated that the concentration of S03 in the molten glass flowing out from the melting tank [S03] was 22.1 ppm. The calculated value of the above formula (a) was When the number of the bubbles in the glass plate is measured for the glass plate obtained by molding the molten glass after the vacuum degassing treatment, it is 0.36 pieces/kg. INDUSTRIAL APPLICABILITY The vacuum degassing method according to the present invention It is possible to provide the most suitable vacuum defoaming conditions for a plurality of alkali-free glasses having different viscous properties. As a result, the number of bubbles in the molten glass after the vacuum degassing treatment can be greatly reduced, and bubbles can be obtained. Low-quality, high-quality glass, especially in the manufacture of liquid crystal display components that are required by Wigger to have no bubble defects, LCD TVs, plasma display TVs, organic EL components, organic EL TVs, and various flat panel display glasses. When the substrate is The method of the invention is very useful. The entire contents of the specification, the scope of the application, the drawings and the abstract of the Japanese Patent Application No. 2010-099611, filed on Apr. BRIEF DESCRIPTION OF THE DRAWINGS [Fig. 1 is a cross-sectional view showing a configuration example of a vacuum degassing apparatus using the vacuum degassing method of the present invention. 20 201204664 Fig. 2 is a drawing of the relationship with [S03] The graph is a graph in which the relationship between the calculated value of the formula (a) and the number of bubbles (bubble density) in the glass plate is plotted. [Description of main component symbols] 1...Decompression defoaming device 14...Down pipe 11...Reducing tank 15...Insulation material 12...Decompression degassing tank 20...Solution tank 13 ...rise tube G...Hyun glass 21

Claims (1)

201204664 VII. Patent application scope: 1. A vacuum degassing method for molten glass, which is to decompress molten glass by flowing molten glass inside a vacuum degassing tank which has been maintained under reduced pressure. The method for defoaming is characterized in that: the molten glass is an alkali-free glass, and the method is a viscosity 77 (Pa · s) of the molten glass when the degassing tank is passed through a vacuum, and a concentration of the s〇 3 of the molten glass [S03 (ppm) The vacuum degassing was carried out under the condition of the following formula (1): 18.2 + 1003 / η - l. 〇 5x [S03] ^ 8 (1). 2. The vacuum degassing method for molten glass according to the scope of the patent application, wherein the s〇3 concentration [S03] (ppm) satisfies the following formula (2): [S03] = -0.0775xTmax + 135.02 .. (2) (In the above formula, 'the maximum temperature α of the molten glass of TmxS in the melting tank)). 3. The vacuum degassing method for molten glass according to claim 1 or 2, wherein the viscosity of the molten glass is set to 12 Pa 2d Pa · s and the temperature is set to 12 (° ' 前述 前述 前述 前述 满足 满足 满足2-120. (:~~2-10. (4. The vacuum degassing method of the molten glass according to any one of the above claims 1 to 3, wherein the aforementioned S03 concentration [S03] is 3~ The method of vacuum degassing of molten glass according to any one of claims 1 to 4, wherein the aforementioned Τ χ χ is 1400 to 1700 t. 6. In the scope of claims 1 to 5 Any of the reduced pressure of molten glass 22 201204664 Defoaming method, wherein the alkali-free glass contains the following components (expressed in mass ° / 〇): Si02: 50~66%; A1203: 10.5~220/〇; B2〇 3: 0 to 12%; MgO: 0 to 8%; CaO: 0 to 14.5%; SrO: 0 to 24%; BaO: 0 to 13.5%; MgO + CaO + SrO + BaO: 9 to 29_5%.