TW201130760A - Method for vacuum-degassing molten glass and process for producing glass product - Google Patents

Abstract

Disclosed is a method in which optimal vacuum-degassing conditions are used when a molten glass is vacuum-degassed using a chloride-based clarificant. The method for vacuum-degassing a molten glass comprises passing the molten glass through a vacuum-degassing tank, the inside of which is kept in a vacuum state, to thereby vacuum-degas the molten glass. The method is characterized in that the molten glass is an alkali-free glass, and that the internal pressure of the vacuum-degassing tank during the vacuum degassing is kept not higher than the bubble growth initiation pressure for the molten glass, Pbg (mmHg), but not lower than the reboiling pressure for the molten glass, Prb (mmHg).

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vacuum degassing method for molten glass, and a method for producing a glass product using the vacuum degassing method.

BACKGROUND OF THE INVENTION Heretofore, in order to improve the quality of a formed glass product, a clarification step of removing bubbles generated in the molten glass before forming the molten glass in which the raw material of the melting furnace is melted by a molding apparatus is used. In the clarification step, a method is known in which a clarifant is added to a raw material in advance, and the molten glass obtained by melting the raw material is stored at a predetermined temperature for a certain period of time, whereby a clarifying agent is used. The bubbles in the molten glass grow up and are removed. Further, a vacuum degassing method is known in which a molten glass is introduced into a reduced-pressure atmosphere gas, and bubbles in a continuously flowing molten glass flow are greatly grown under the reduced-pressure atmosphere gas to be contained in the molten glass. After the bubbles are floated, broken, and removed, the gas is discharged from the decompressed atmosphere. In order to effectively remove the bubbles from the molten glass, it is preferred to combine the above two methods to carry out the depressurization defoaming method by using a blooming surface to which a clarifying agent is added. As a clarifying agent for glass, there are oxide-based clarifying agents such as As2〇3, Sb2〇3, and Sn〇2; sulphate-based clarifying agents such as CaS〇4 and BaS〇4; and gasification of metal such as smear (4) Clarifying agent, etc. Among these, # sulfate clarifier

S 201130760 When the glass is low-inspection, the effect of removing bubbles from the glass is not sufficient due to the low degree of rotation of SO. Moreover, since ~2〇3 and 讥2〇3 (especially As2〇3) have an environmental load, it is necessary to suppress their use. In addition, Sn〇2 will release oxygen at temperatures up to 15 〇〇. 〇 Above, and it is difficult to use it effectively as a clarifying agent. Further, when a sufficient amount of the alkali metal vapor is added to the clarification, the alkali metal is contained in the alkali-free glass, and thus it is an unacceptable proof. The present inventors first investigated the possibility of being a clarifying agent for an alkali-free glass, and as a result, it was found that a chlorine-containing compound exerts an excellent effect as a clarifying agent in combination with a vacuum degassing. Such a vapor clarifying agent is, for example, BaC12,

SrCl2, CaCl2, MgCl2, A1C13 and ΝΗ4α. Conditions such as pressure or temperature in the vacuum degassing tank at the time of performing vacuum degassing are shown in Patent Documents 1, 2 and the like. CITATION LIST Patent Literature Patent Literature 1: International Publication No. WO2008/029649 (Patent Document 2) International Publication No. WO2008/093580 SUMMARY OF INVENTION Summary of the Invention The present inventors have found that 'when chlorine such as NH4C1 or SrCl2 is used When the clarifier for a compound is used as a clarifying agent for an alkali-free glass, the ratio of the chloride contained in the glass composition to 201130760 may affect the suitable conditions for decompression and defoaming. The present invention is based on the above-mentioned knowledge, and an object thereof is to provide a vacuum degassing method for an alkali-free glass which can provide optimum conditions for decompression and defoaming when degassing under reduced pressure using a chloride-based clarifying agent. 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 molten glass into a vacuum degassing vessel which has maintained the inside in a reduced pressure state, thereby reducing A method for defoaming molten glass, characterized in that the molten glass is an alkali-free glass, and the pressure in the vacuum degassing tank at the time of performing vacuum degassing is maintained at the following formula (1) or formula ( 2) The bubble growth start pressure Pbg (mmHg) or less of the molten glass is not less than the reboil pressure Prb (mmHg) of the molten glass represented by the following formula (3): • Pbg=(2.6082xT2-3538.2)x [P-OH]+(-1.2102xT2+2612.2)x [Cl]-80.3......(1) • Pbg=(-0.2462xT2 + l 121.7)χ[β-ΟΗ]+(1.9714χΤ2-1730.6)x [ Cl]-187.3 (2) • Prb=0.8325xPbg-59.5 (3) (In the above formula, T2 represents the viscosity of the molten glass at a temperature of 102 dPa·s (°C), and [β-〇Η] The β-ΟΗ value (mm·1) of the alkali-free glass, and [Cl] represents the gas content (% by mass) in the alkali-free glass. When [C1] is 0.12 mass% or more, the Pbg system is 1) indicates; when [C1] is not When the content is 0.12% by mass, Pbg is represented by the formula (2). Further, the above-mentioned |>0 print is preferably 0.15 to 0.6〇1111_1, and the above [(:1] is preferably 0.03 to 0.3% by mass. 201130760] The above-mentioned Ding 2 is preferably boo~1750T: Provided is a method for producing a glass product, which is provided with the following steps: a glass melting step, a molten glass material, and a smelting glass bottle; and a vacuum degassing step according to the molten glass And the glass product forming step is a method of forming a molten glass which is defoamed under reduced pressure. Further, the alkali-free glass in the present invention means that it is not in addition to impurities inevitably mixed. Those who have the metal tester, that is, the metal does not contain (4) metal. The effect of the invention is that the vacuum degassing method can be optimized by using the vapor-based clarifying agent for vacuum degassing without surface inspection. Under the condition of decompression and degassing, the result can reduce the bubbles or foreign matter in the smelting glass after the vacuum degassing treatment, and produce the glass with less high functionality and high quality. The vacuum defoaming method of this month is used. Vapor-based clarifying agent, therefore: will be the body ball In addition, the _ product manufactured by using the defoaming method of the present invention does not need to be suppressed for the bubble and does not occur in the recovery of the glass product in the manufacturing plant or the processing plant. The figure is a cross-sectional view of a configuration example of the subtractive defoaming device which is not used in the vacuum degassing method of the present invention. Fig. A. The figure will be I and (4) The relationship between the coefficient a and the plot 3 is a plot plotting the relationship between I and the coefficient b of equation (4). 201130760. Figure 4 shows the relationship between Τ2 and the coefficient c of equation (5). Chart of drawing. Fig. 5 is a graph plotting the relationship between T2 and the coefficient d of equation (5). Fig. 6 is a graph plotting the relationship between the reboiling b and the bubble growth start pressure & Figure #' is not tested _ composition A, B, c 'in the gas content (% by mass) is 0.12 mass / / or more, the bubble growth start pressure & experimental value (mmHg) and bubble growth start pressure The relationship between the calculated value of Pb g (mmHg) is plotted. The brother 8 shows that there is no glass composition a, b, (2, in chlorine (Mass%) at less than 0.12 mass% "bubble growth starting pressure of Pbg Found (mmHg) and the bubble growth starting pressure Calcd Pb g of (mmHg) was added to the chart plot of the relationship.

[Embodiment] J. Mode for Carrying Out the Invention Hereinafter, the vacuum degassing method of the present invention will be described with reference to the drawings. The second drawing shows 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 显示 shown in Fig. i, the cylindrical decompression degassing tank 12 is arranged in the horizontal direction of the long axis alignment, and is accommodated in the decompression chamber 11 by β. Below the one end of the pressure deaeration tank 12, a riser pipe 13 having a vertical direction is attached, and a down pipe 14 is attached below the other end. The ascending official 13 and the downcomer 14 are partially located in the decompression chamber u. The riser 13 is in communication with the vacuum degassing tank 12, and the molten glass G from the melting tank 20 is introduced into the vacuum degassing tank 12. Down tube 14 series with decompression decompression

S 7 201130760 The tank 12 is connected to each other' and the molten glass g defoamed under reduced pressure is led to the next - a treatment tank (not shown). In the inside of the decompression chamber 11, the heat-reducing bricks, such as heat-insulating bricks, and the like, are placed around the decompression defoaming tank 12, the rising potential 13, and the downcomer 14. In the vacuum degassing apparatus 显示 shown in Fig. 1, the vacuum degassing tank 12, the riser pipe 13, and the downcomer 14 are pipes for melting glass, which are excellent in heat resistance and corrosion resistance to molten glass. Made of materials. For example, _ can be made of platinum, platinum alloy, or reinforced platinum made by dispersing metal oxides into platinum or platinum alloys. Further, it may be made of a non-metallic inorganic material, that is, a dense refractory material. Further, it may be a case where the dense refractory is lined with platinum or platinum alloy. In the vacuum degassing method of the present invention, the molten glass G supplied from the melting tank 2 is subjected to vacuum degassing by a vacuum degassing vessel 12 which has been reduced in pressure to a predetermined degree of pressure reduction. The molten glass G is preferably continuously supplied to the vacuum degassing tank 12 and discharged. Further, from the viewpoint of productivity, the flow rate of the molten glass is preferably 200 tons/day. In order to prevent a temperature difference from the molten glass G supplied from the melting tank 20, the degassing defoaming tank 12 is preferably heated to 1200 ° C to 1600 ° C inside, and is preferably heated to a temperature of 1350 t > 1550 ° C. The molten glass G used in the vacuum degassing method of the present invention is a non-existing glass, and the following vapor-based clarifying agent is added to a glass raw material for producing a glass-free glass. Specific examples of the chloride-based clarifying agent include, for example, at least one selected from the group consisting of BaCl2, SrCl2, CaCl2, MgCl2, A1C13 & NH4C1. Among them, BaCl2, SrCl2, CaCl2, MgCl2, etc. 201130760 The soil-like chloride or salt hydrate is the same as 丨3 and NH4C1_. Therefore, from the viewpoint of no troubles caused by deliquescence, as a clarifying agent for the production of the glazing of the present invention, the addition of Baci2·2Η2〇,

SrCl2 · 6Η2〇 and NH4CI are preferred. The chlorine content in the non-test glass (hereinafter sometimes referred to as [(3) in the present specification) is preferably 0.03 to 0.3% by mass. (6) (10) 〇 5 ~ 〇 25% by mass is better. When [C1] is less than 0.03 mass%, there is a lack of clarification effect of the glass. Furthermore, as a chlorinated (iv) clarifying agent, although the use of metal oxides is also considered, if a sufficient dose is added to the clarification of the molten glass, it will cause a metal test in the glass. The clarifying agent formed by the vaporization of the metal is not suitable. When the vacuum degassing is performed, the air in the decompression chamber is passed through the suction opening portion 16 provided at a predetermined position in the decompression chamber 11, and is externally vacuum-reduced by a vacuum decompression mechanism (not shown). exhaust. Thereby, the air contained in the vacuum degassing tank 12 housed in the decompression tank u can be indirectly exhausted, and the decompression degassing tank can be internally depressurized to a predetermined pressure. In the vacuum degassing method of the present invention, the pressure in the vacuum degassing tank 12 is maintained at or below the bubble growth start pressure Pbg (mmHg) expressed by the following formula (丨) or (2). • Pbg=(2.6082xT2-3538.2)x[p-〇H]+(-1.21〇2xT2+2612.2)x [C1J-80.3...(1) • Pbg=(-〇.2462xT2 + 1121.7) x[p-〇H]+(1.97l4xT2-i730.6)x [C1J-187.3 (7) Here, [Cl] in the formulas (1) and (2) is not without glass The chlorine content in the 201130760 (Berry%). When [Cl] is 〇_12% by mass or more, the bubble growth start pressure Pbg is expressed by the above formula (1). On the other hand, when [Cl] is less than 12% by mass of G, Pbg is represented by the formula (2). In the formula (2), (2), the viscosity of the molten glass is 102 dPa·s / the degree of the dish (C) can be measured using a high temperature rotational viscometer. The viscosity of 10 dPa . s shows that the viscosity of the glazed glass has a sufficiently low basic viscosity. Therefore, the viscosity of the molten glass is 1 〇 2 dPa·s, and the temperature A is the reference temperature of the fused glass, and is 1500 to 1750 〇C when it is used for the TFT liquid crystal display substrate. When I is 1500 to 1720 ° C, the molten glass makes it easy to float, and has excellent defoaming performance at the time of vacuum degassing. T2 is preferably 1560 to 1700 ° C, and is 159 〇 to 168 。. ^ Better. In the formulas (1) and (2), '[β_〇Η] indicates the β_〇Η value (mm) of the glass without the test. The β-OH value is used as an indicator of the amount of water in the glass. The transmittance of the alkali-free glass test piece in which the molten glass after defoaming under reduced pressure was formed into a plate shape was measured using a Fourier transform infrared spectrometer (FT_IR), and the β-ΟΗ value was obtained by the following formula. • β-OH value = (i/x)logl〇(T|/T2) • X : glass thickness (mm) • Τι : transmittance in reference wave number 4000cm·1 (%) • I: hydroxyl absorption wave number The minimum transmittance (0/〇) near the 3570 cm-i is preferably 0.15 to 0.6 mm of the alkali-free glass. The β-ΟΗ value of the alkali-free glass is governed by the amount of water in the raw material, the concentration of water vapor in the melting tank, and the combustion method (oxygen combustion, air combustion). The method for adjusting the β-OH of the gas concentration in the melting tank 10 201130760 will be described later. The p_〇H value is preferably 〇·2 to 0.55 mm 1 . Furthermore, the β_〇Η value is generally the value of β-0Η after vitrification. In the present specification, the bubble growth start pressure Pbg is defined as follows. Under the condition that the temperature is constant, when the vacuum degassing tank 12 has been decompressed, the volume of the bubbles in the molten glass stored in the vacuum degassing tank 12 (the bubble is directly increased according to the wave law of the wave. However, Once the pressure in the vacuum degassing tank 12 is reduced [to a certain degree of pressure, the volume of the bubble in the smelting glass (the diameter of the bubble) will break the wave of the ear and the rapid increase. This pressure is called the bubble growth start pressure. When the pressure in the vacuum degassing tank 12 is kept below the bubble growth start pressure Pbg (mmHg), the bubbles contained in the molten glass can be sufficiently grown in the vacuum degassing tank 12. In the present invention, the bubble growth start pressure Pbg can be obtained in the following order. In order to reproduce the condition in the vacuum degassing tank 12, the quartz glass containing the alkali-free glass swarf is prepared. The crucible is placed in a vacuum decompression vessel. The crucible is heated to a predetermined temperature (for example, 1300. (or 1400. 〇, so that the alkali-free glass is melted. Although no glass is completely melted), the vacuum decompression vessel is placed inside. Decompression and observation of the fused glass The diameter of the bubble. To observe the diameter of the bubble in the molten glass, for example, a bubble detector can be used to detect the bubble in the molten glass from the detection window of the vacuum decompression container. Further, the bubble sample for measuring the bubble diameter can be used. The number is more than 2 。. As the pressure in the vacuum decompression vessel drops, the bubble in the smelting glass will increase according to the law of the wave. However, once the vacuum decompression container

11 S 201130760 Internal pressure reduction to a certain range of force, the diameter of the bubbles of the secret glass will break the wave of the ear law and eager to add. The pressure reduction degree in the positive line pressure vessel at this time is the bubble growth start pressure pb g. The inventors of the present application have intensively reviewed the relationship between the bubble growth start pressure Pbg and the various parameters associated with the vacuum defoaming of the alkali-free glass, and found that the viscosity of the molten glass is 102 dPa·s (d 2), The ρ·〇Η value of the alkali glass ([β-ΟΗ]) and the chlorine content ([C1]) in the alkali-free glass affect the bubble growth start pressure Pbg. According to this knowledge, the relationship between the bubble growth start pressure Pbg and τ2 '[β-OH] and [C1] is experimentally derived, and is the above formulas (1) and (2). Hereinafter, the order of derivation of the equations (1) and (2) will be described in more detail. For the alkali-free glass Α~C of Τ2, prepare the alkali-free glass with β-〇Η value [β-ΟΗ] of alkali-free glass or gas content [C1] in alkali-free glass, and other composition values are the same. And the bubble growth start pressure Pbg is calculated in the above order. Here, NI^Cl is used in the vapor clarifier. Although it will be described later in detail, when the refining tank 20 is used to disperse the glass, the β-〇Η value of the alkali-free glass can be adjusted by adjusting the ratio of the fuel to the air. The composition without alkali and Τ2 are as follows. The composition of the following alkali-free glass is based on the mass of the compound. /. Said. (alkali-free glass crucible)

Si〇2 : 59.5 mass ° / 〇, Α! 2 〇 3 : 17.7 mass %, Β 2 〇 3 : 7.9 mass %,

Mg〇 : 3.2% by mass,

CaO : 3.7 mass%, 12 201130760

SrO : 7.9 mass%,

BaO : 0.1% by mass. (T2 : 1660°〇 (no glass test)

Si02 : 59.4% by mass,

Al2〇3 : 16.9 mass%, B203: 8.6 mass%,

MgO : 4.0% by mass,

CaO : 5.4% by mass,

SrO : 5.7 mass%,

BaO : 0.0 mass %. (T2: 1617°〇 (alkali-free glass C)

Si02 : 59·5 mass%, Α12〇3 : 17.0 mass%, Β2〇3 : 8.0 mass%,

MgO : 4.7 mass ° / 〇,

CaO : 6.0% by mass,

SrO : 4.8 mass%,

BaO : 0.0% by mass. (T2: 1597〇C) It is found in each of the alkali-free glasses A to C that when the chlorine content [C1] in the alkali-free glass is 0.12% by mass or more, the bubble growth start pressure Pbg, and the glass-free β-ΟΗ The value ([β-ΟΗ]) and the gas content in the alkali-free glass ([C1]) will hold the following

S 13 201130760 The relationship expressed by equation (4). • Pbg=ax[p-OH]+bx[Cl]-80.3 (4) Corresponding to the formula (4) of each alkali-free glass A to C as follows (no glass A) • Pbg =800.6x[P-OH]+660.1x[Cl]-80.3......(4_A) (no glass B) • Pbg=650.0x[p-OH]+664.9x[Cl]-80.3. .....(4-B) (alkali-free glass C) • Pbg=646.9x[P-OH]+672.8x[Cl]-80.3......(4-C) Figure 2 is based on As a result of the above, a graph plotting the relationship between T2 and the coefficient & Figure 3 is a graph plotting the relationship between Τ2 and the coefficient b of equation (4) based on the results obtained above. According to the regression line shown in Fig. 2 (1) and Fig. 3, the above formula is used. On the other hand, when the chlorine content in the alkali-free glass is less than 12 cups, Pbg, [β-ΟΗ is found. ], [C1] will be established by the following formula: • Pbg=cx[p-OH]+dx[Cl]-187.3 (5) Corresponding to the formula of each alkali-free glass A~C (5) ) are as follows. (No glass A) relationship. Pbg=713.6x[p-〇H]+1530.0x[Cl]-i87 3 (no glass B) • Pbg=721.7x[P-〇H]+1494.6x[Cl ]-i87 3 (alkali-free glass C) (5-B) .Pbg=729.8x[p-〇H]+1392.1x[Cl]-l87 3 (5-C) 14 201130760 Figure 4 is based on the above As a result, a graph plotting the relationship between Τ2 and the coefficient c of the equation (5) is plotted. Figure 5 is a graph plotting the relationship between T2 and the coefficient d of equation (5) based on the results obtained above. The operator of the regression line shown in Figs. 4 and 5 is the above formula (2). As described above, in the vacuum degassing method of the present invention, the pressure in the vacuum degassing vessel 12 is maintained at a bubble growth start pressure Pbg (mmHg) expressed by the above formula (1). When the pressure in the bubble tank 12 is extremely low, the molten glass flowing in the vacuum degassing tank 12 may be reboiled. Therefore, in the vacuum degassing method of the present invention, the pressure in the vacuum degassing vessel 12 is maintained at a pressure equal to or higher than the reboil pressure Prb (mmHg) of the molten glass represented by the following formula (3). • Prb = 0.8325xPbg - 59.5 (3) In this specification, the reboiling pressure Prb is defined as follows. In order to sufficiently grow the bubbles contained in the molten glass, it is preferable to lower the pressure in the vacuum degassing tank 12 as much as possible. However, when the pressure in the vacuum degassing vessel 12 is extremely lowered, bubbles may be generated at the interface of the glass which is in contact with the molten defoaming tank 12 made of platinum or platinum alloy or the dense refractory. This phenomenon is called reboil, and the pressure in the vacuum degassing tank 12 at this time is called reboil pressure Prb. Further, the reboiling pressure Prb can be obtained in the following order. In order to reproduce the inside of the vacuum degassing tank 12, a quartz glass crucible containing glass particles of alkali-free glass was placed in a vacuum decompression vessel. The hydrazine is heated to a predetermined temperature (for example, 1300 ° C or 1400 ° C) to melt the alkali-free glass.

S 15 201130760 A test piece made of a material (white gold or platinum alloy or dense refractory) which constitutes the glass contact surface of the vacuum degassing tank, which is a material which constitutes the vacuum degassing tank. Soak into the molten glass. In this state, the inside of the vacuum decompression vessel was gradually decompressed and the generation of bubbles in the glass interface of the test piece was observed. The degree of depressurization of the vacuum decompression vessel at the time of generating bubbles at the glass interface is the reboiling pressure prb. The inventors of the present application have intensively reviewed the relationship between the reboiling pressure prb and the various parameters associated with the vacuum degassing of the alkali-free glass, and found that there is a specific relationship between the reboiling pressure Prb and the bubble growth starting pressure Pbg. Established. The above formula (3) can be specified by plotting the relationship between the reboiling pressure Prb and the bubble growth starting pressure Pbg. Fig. 6 is a graph showing the relationship between the reboiling pressure prb and the bubble growth start pressure pb g as a green map. In Fig. 6, the test piece immersed in the molten glass was made of platinum, ruthenium gold (platinum 9 〇 mass%, 铑1 〇 mass%). Further, the alkali-free glass A to c was used as the molten glass. The temperature of the molten glass was 1400 °C. In the vacuum degassing method of the present invention, the pressure in the vacuum degassing vessel 12 is maintained at a pressure equal to or higher than the reboiling pressure prb (mmHg). When the Lili in the vacuum degassing tank 12 is maintained at a reboiling pressure Pr b (mmHg) or more, it is possible to prevent reboiling in the molten glass flowing through the decompression defoaming tank 12. Therefore, the number of bubbles remaining in the molten glass after the vacuum degassing treatment can be reduced to produce a highly functional and high quality glass having less bubbles. In other words, in the vacuum degassing method of the present invention, the pressure in the vacuum degassing vessel 12 is maintained at a bubble growth start pressure pb g (mmHg) expressed by the above formulas (1) and (2). And maintaining the reboiling pressure expressed by the above formula (3) 16 201130760

Prb (mmHg) or more 'can increase the bubble contained in the molten glass in the vacuum degassing tank I2, and can efficiently remove the bubbles in the molten glass, and the other side can also prevent the flow in the vacuum degassing tank 12 In the dazzling glass, there is a situation in which it is produced. As a result, the emulsions remaining in the molten glass after the vacuum degassing treatment are extremely reduced, and a highly functional and high-quality glass having few bubbles can be produced. The first example of the alkali-free glass to be used in the vacuum degassing method of the present invention is preferably a composition containing an alkali-free glass of the following composition, expressed by mass% in terms of the following oxide.

Si02 : 50 to 66% by mass,

Ak〇3 : 10.5~24 mass 〇/〇, B2〇3 : 0~12% by mass,

MgO : 〇~8 mass%,

CaO : 〇~14.5% by mass,

SrO : 〇~24% by mass,

BaO : 〇~13.5% by mass, and

Mg〇+Ca0+Sr0+Ba0: 9 to 29 5 mass%. The second example of the alkali-free glass to be used in the vacuum degassing method of the present invention is preferably a composition of, for example, the mass% of the following gasification, and the composition of the alkali-free glass having the following composition. 8 Magic 2: 58~66% by mass,

Al2〇3 : 15 to 22% by mass, B2〇3: 0 to 12% by mass,

MgO : 〇 ~ 8 mass. /〇,

S 17 201130760

CaO : 0 to 9 mass%,

SrO : 3 to 12.5 mass%,

BaO : 0 to 2% by mass, and MgO + CaO + SrO + BaO : 9 to 18 mass ° / 〇. The reason for limiting the range of each component of the above alkali-free glass composition will be described below.

When Si〇2 exceeds 66%, the refining property of the glass is lowered and it is liable to be devitrified. It is preferably 64% or less, more preferably 62% or less. When it is less than 5〇%, the specific gravity increases, the strain point decreases, the coefficient of thermal expansion increases, and the chemical corrosion resistance decreases. It is preferably 58% or more, more preferably 58 5% or more, and still more preferably 5 9% or more.

Al2〇3 is necessary to suppress the phase separation of the glass and increase the composition of the strain point. When it exceeds 24%, it is easy to cause devitrification and chemical corrosion resistance. Preferably, it is 22% or less, more preferably 20% or less, and still more preferably 18% or less. Less than 10.5°/. At the time, the glass is easily separated, or the strain point is lowered. It is preferably Μ% or more, more preferably 15.5% or more, and still more preferably 16% or more. Although B2〇3 is not essential, it is a component which can reduce the specific gravity, improve the melting property of glass, and is difficult to devitrify. When it exceeds 22%, the strain point is lowered, the chemical corrosion resistance is lowered, or the sublimation at the time of glass mystery is made remarkable, and the glass heterogeneity b is preferably 12% or less, and more preferably 9%. the following. Less than 5. /. When the weight is increased, the glass transition property is lowered, and the glass is easily devitrified, it is preferably 5% or more, more preferably 6% or more, and more preferably

Although Mg〇 is not necessary, it is a component that can reduce the specific gravity and improve the leaching property of 18 201130760. Above 8%, the glass will be susceptible to phase separation, devitrification, or reduced chemical age. It is preferably 6% or less and more preferably 5% or less. When Mg? is contained, it is preferable to contain 1% or more. In particular, it is preferable to contain 3% or more in order to maintain the deliability and at the same time reduce the specific gravity.

Although CaO is not required, it can improve the devitrification property of the glass and is difficult to devitrify, so it can be contained in an amount of 14.5% or less. When it exceeds 145%, the specific gravity will increase, causing the thermal expansion bond to become larger, and on the contrary, it will be devitrified. It is preferably below the state, more preferably 8% or less, and still more preferably 7% or less. It is preferable to contain (5) so as to contain 2% or more. More preferably, it is more than 35%.

SrO is a component that inhibits phase separation of glass and is difficult to devitrify. When it exceeds 24%, the specific gravity increases to increase the coefficient of thermal expansion, and on the contrary, it is easy to devitrify. It is preferably 12.5% or less, more preferably 10.5% or less, still more preferably 85% or less. In consideration of the addition of chloride as a clarifying agent, it is preferable to use the &^^ · 6H2〇 or BaCb · 2 out of the viewpoint that it is not easily deliquescent and tends to remain in the glass when the raw material is melted. In order to make the addition amount of (^) have a degree of freedom, it is preferable that the glass component contains Sr〇 of 3% or more. Since the addition amount of C1 is limited when & ◦ is less than 3%, it is not appropriate. It is preferably 4% or more, and more preferably 4.5% or more. Since BaO can suppress phase separation of glass and is difficult to devitrify, it can be contained in an amount of 13 〇 5 〇 /. When it exceeds 13.5%, the specific gravity increases and thermal expansion The coefficient is large, preferably 2% or less, more preferably 1% or less, still more preferably 〇1% or less. In particular, when weight reduction of the glass substrate is emphasized, it is preferable that it is substantially not contained.

As. 〇3 and Sh>2 〇3 are inevitably mixed as impurities or the like

S 19 201130760 is preferably not contained (ie, substantially not contained). In addition, in order to improve the meltability, etc., it is possible to contain other trace components of ZrOO in a total amount of 5 mass% or less in the range which does not violate the object of this invention. According to the vacuum degassing method of the present invention, for example, the following non-alkali glass D containing a large amount of SiO 2 and Α 12 〇 3 is contained in comparison with the above-mentioned alkali-free glass Α C C (in terms of the following oxides) It is also possible to carry out vacuum degassing under the optimum conditions, and to obtain an effect of reducing the generation of bubbles or foreign matter. (No glass D)

Si02 : 62% by mass, A1203: 20% by weight, B203: 0% by mass,

MgO : 4.7 mass%,

CaO : 4.4% by mass,

SrO : 8.1% by mass,

Zr02 : 0.9 mass 0 / 〇, and (T2 : 1690 ° C) In the vacuum degassing method of the present invention, a chloride-based clarifying agent may be used in combination as a clarifying agent. In this case, other clarifying agents which can be used in combination include, for example, S03, F, Sn02 and the like. These other clarifying agents may be contained in the alkali-free glass in an amount of 2% by mass or less, preferably 1% by mass or less, and more preferably 0.5% by mass or less. In the vacuum degassing method of the present invention, it is sometimes necessary to adjust [β-ΟΗ], that is, to adjust the amount of water of the molten glass. The amount of water in the molten glass, 20 201130760, can be adjusted by varying the composition of the gas mixed with the fuel (i.e., changing the ratio of oxygen to air mixed with the fuel) when the fuel is burned. The dimensions of the constituent elements of the vacuum degassing apparatus used in the vacuum degassing method of the present invention can be appropriately selected as required. The size of the vacuum degassing tank is not limited to that of the vacuum degassing tank, which is made of platinum or platinum alloy, or is sensitive to fire, and can be appropriately selected in accordance with the vacuum degassing apparatus to be used. The case 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) When the vacuum degassing tank 12 is made of platinum or platinum alloy, the thickness is preferably 0.5 to 4 mm. The decompression chamber 11 is made of metal (for example, made of stainless steel) and has a shape and a size that can accommodate a decompression degassing tank. The riser pipe 13 and the downcomer pipe 14 can be appropriately selected depending on the vacuum degassing apparatus to be used, whether it is made of platinum or platinum alloy or a dense refractory. For example, the size 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 platinum alloy, the thickness is preferably 0.4 to 5 mm. The method for producing a glass product of the present invention has the following steps: a glass melting step, which is a molten glass raw material, and a method for producing molten glass; and a vacuum degassing step, which is based on the aforementioned vacuum glass defoaming method.

S 21 201130760; and the glass forming step ′ is to form the (four) glass which has been defoamed under reduced pressure. The glass refining step may be carried out by a glass-blending method as conventionally known, for example, by heating a glass raw material which is blended correspondingly to the glass type to dl4G〇C or more to thereby melt the predetermined glass raw material. The glass raw materials used are also as long as they are suitable for the production of raw materials without glass, that is, there is no particular limitation. For example, Shi Xi Shi Shao, shout, limestone, oxidized Shao, carbonic acid, magnesium oxide and others are well known. A raw material of a glass component, and a handle material blended in such a manner as to constitute a composition of the intended alkali-free glass product can be used. The above-mentioned (iv) vapor-based clarifying agent in the present invention is added to the glass raw material in a predetermined amount. Further, the glass product forming step can also employ a forming method of a glass article which has hitherto been known. When a glass plate is produced as a glass product, various molding methods such as a float sheet glass forming method, a rolled out forming method, and a fusion forming method can be used. EXAMPLES Hereinafter, the present invention will be more specifically described based on examples. However, the present invention is not limited to these. (Example 1) In the present example, NH4C1 was added as a vapor clarifying agent using an amorphous glass A ^ previously known as [β-ΟΗ] of 0.29 mm·1. Further, the mass % of the total mass after the vitrification is 0.20 mass. /. The amount of NH4C1 added is calculated by the above formula (1), and the bubble growth start pressure Pbg is 270 mmHg 〇 22 201130760. From the Pbg obtained here and the above formula (3), the reboiling pressure Prb is 165 mmHg 0 and the width is 45 mm. A platinum alloy of Pt90%/Rhl0% having a depth of 7 mm and a thickness of 1 mm was placed in a quartz glass container having a width of 50 mm x a depth of 10 mm and a height of 50 mm, and a block-shaped alkali-free glass A50g was placed. Thereafter, the quartz glass container was placed in an electric furnace and heated up to 1400 ° C to melt the alkali-free glass A. Next, the ambient gas pressure of the electric furnace was reduced to a predetermined pressure, and the amount of bubbles in the molten glass was observed. Further, the amount of the bubble in the molten glass can be visually confirmed from the detection window provided on the side of the electric furnace. When the ambient gas pressure of the electric furnace was maintained at a reboil pressure Prb of 165 mmHg or more and the bubble growth start pressure pbg was 27 〇mmHg or less, it was confirmed that the amount of bubbles remaining in the molten glass was extremely small. On the other hand, 'when the ambient gas pressure of the electric furnace is maintained at the reboil pressure Prb of less than 165 mmHg, the amount of bubbles generated from the platinum plate in the molten glass is significantly increased, so that the bubbles remaining in the molten glass can be confirmed. The amount is very large. (Example 2) In the present example, the mass of the mass after the vitrification of chlorine in the non-experimented glass A was excluded. /◦ is 〇·〇7 quality. The same procedure as in Example 1 was carried out except that NH4C1 was added in an amount. From the above formula (2), the bubble growth start pressure Pbg was 127 mmHg. From the Pbg obtained here and the above formula (3), the reboil pressure Prb was 46 mmHg. In the electric furnace, the ambient gas force is maintained at a reboiling pressure Pr b of 46 mmHg.

When the bubble growth start pressure Pbg is 127 mmHg or less, it is confirmed that the amount of bubbles remaining in the molten glass is extremely small. On the other hand, when the pressure of the private gas of the electric furnace is maintained at a pressure of less than 46 mmHg, it is found that the amount of bubbles generated from the platinum plate in the molten glass is remarkably increased, so that it is confirmed that it remains in the molten state. The amount of bubbles in the glass is very large. (Example 3) In the present example, an unexamined glass B in which [β-OH] was previously known to be 0.29 mm-1 was used. NH4C1 was added as a chloride fining agent. Further, ΝΗ4α is added by the mass % of chlorine to the total mass after vitrification, which is 量.2〇 mass ❶/◦. Calculated by the above formula (1), the bubble growth start pressure is 1 241111111. From the Pbg obtained here and the above formula (3), the reboil pressure Prb was 147 mmHg. A platinum alloy of Pt 90%/Rhl 0% having a width of 45 mm, a depth of 7 mm and a thickness of 1 mm was placed in a quartz glass vessel having a width of 50 mm x a depth of 10 mm and a height of 50 mm, and a block-shaped alkali-free glass B50g was placed. Thereafter, the quartz glass container was placed in an electric furnace and heated up to 1400 ° C to melt the alkali-free glass B. Next, the ambient gas pressure of the electric furnace was depressurized until the predetermined pressure was stopped, and the amount of bubbles in the molten glass was observed. Further, the amount of the bubble in the molten glass can be visually confirmed from the detection window provided on the side of the electric furnace. When the ambient gas pressure of the electric furnace is maintained at a reboil pressure Prb of 147 mmHg or more, and the bubble growth start pressure is maintained. When 4 was 248 〇 11111 Ω or less, it was confirmed that the amount of bubbles remaining in the molten glass was very small. On the other hand, when the ambient gas pressure of the electric furnace is maintained at the reboil pressure Prb of less than 24 201130760 147 mmHg, since the amount of bubbles generated from the platinum plate in the molten glass is remarkably increased, it is confirmed that it remains in the molten glass. The amount of bubbles is very large. (Example 4) In the present Example, the same as in Example 3 except that nh4C1 was added in an amount of 7% by mass of the total mass after the vitrification in the alkali-free glass B. The way to implement it. The bubble growth start pressure pbg obtained by the above formula (2) is i25 mmHg. From the hydrazine obtained here and the above formula (3), the reboil pressure Prb was 45 mmHg. When the gas pressure of the electric furnace was maintained at a pressure of 45 mmHg or more and the bubble growth start pressure Pbg was 125 mmHg or less, it was confirmed that the amount of bubbles remaining in the glass was extremely small. On the other hand, when the ambient gas pressure of the electric furnace is maintained at a reboil pressure Prb of less than 45 mmtlg, it is found that the amount of bubbles generated from the platinum plate in the molten glass has a significant increase in the number of ports, so that it remains in the molten glass. The amount of bubbles is very large. (Example 5) In the present example, 'alkali-free glass C having a known [β·0Η] of 0 29 mm-! was used. NH4C1 was added as a chloride fining agent. Further, NH4 C1 was added in an amount of 0% by mass based on the mass% of the total mass after the vitrification. From the above formula (1), the bubble growth start pressure pbg was 237 mmHg. From the pbg obtained here and the above formula (3), the reboil pressure Prb was 138 mmHg. 25 201130760 The platinum alloy of 45mm, depth 7mm, thickness imm pt9〇%/RhlO% is placed in a quartz glass container with a width of 50mmx deep i〇mmx and a height of 5〇mm, and a block-shaped alkali-free glass C5〇 is placed. g. Thereafter, the quartz glass container was placed in an electric furnace and heated until 14 〇〇1 to melt the alkali-free glass c. Then, the ambient gas pressure of the electric furnace was depressurized until the predetermined pressure was reached, and the amount of bubbles in the molten glass was observed. Further, the bubble enthalpy in the molten glass can be visually confirmed from the detection window provided on the side of the electric furnace. When the ambient gas pressure of the electric furnace was maintained at a reboiling pressure prb of 138 mmHg or more and the bubble growth start pressure Pbg was 237 minHg or less, it was confirmed that the amount of bubbles remaining in the molten glass was extremely small. On the other hand, when the ambient gas pressure of the electric furnace is maintained at a reboil pressure Prb of less than 138 mmHg, since the amount of bubbles generated from the platinum plate in the molten glass is remarkably increased, the bubbles remaining in the molten glass can be confirmed. The amount is very large. (Example 6) In the present example, in addition to the alkali-free glass C, the mass % of the total mass after the vitrification of the gas is 〇.〇7 mass%, and the addition of ^114 (:1, The bubble growth start pressure Pbg was i23 mmHg calculated from the above formula (2). From the Pbg obtained here and the above formula (3), the reboil pressure Prb was 43 mmHg. When the ambient gas pressure of the electric furnace is maintained at a reboil pressure Prb of 43 mmHg or more, and the bubble growth start pressure is maintained at 4,311,111,111 cm or less, it is confirmed that the amount of bubbles remaining in the molten glass is extremely small. 201130760 The electric pressure of the electric furnace of the electric furnace is maintained at a pressure of Pr b of less than 43 mmHg. Since the amount of bubbles generated from the platinum plate in the molten glass is significantly increased, it is confirmed that the amount of bubbles remaining in the glazed glass is very large. (Example 7) In the present example, a non-existing glass D having a T2 of 1690 ° C and a [β-ΟΗ] of 0.29 mm 1 was used in advance, and a force NH4C1 was added as a vapor clarifier. The quality of the total mass after the vitrification is 〇.2〇 From the above formula (1), the bubble growth start pressure Pbg is 285 mmHg. From the Pbg obtained here and the above formula (3), the reboiling pressure prb is 178 mmHg, and the width is 45 mm. A platinum alloy of Pt90%/Rhl0% with a depth of 7 mm and a thickness of 1 mm is placed in a quartz glass container having a width of 50 mm x a depth of 10 mm and a height of 50 mm, and a block-shaped alkali-free glass D50g is placed. Thereafter, the quartz glass container is placed in an electric furnace for heating. The alkali-free glass D is melted until 1475 ° C. Next, the ambient gas pressure of the electric furnace is reduced to a predetermined pressure, and the amount of bubbles in the molten glass is observed. Further, the amount of bubbles in the molten glass can be set from The detection window on the side of the electric furnace was confirmed by visual inspection. When the pressure of the ambient gas of the electric furnace was maintained at a reboil pressure Prb of 178 mmHg or more and the pressure was raised at the beginning of the bubble growth, it was confirmed to be in the molten glass. On the other hand, when the ambient gas pressure of the electric furnace is maintained at a reboil pressure Prb of less than 178 mmHg, a significant increase in the amount of bubbles generated from the platinum plate in the molten glass is found. It can be confirmed that the amount of bubbles remaining in the molten glass is much more than 27 201130760. (Embodiment 8) In the present embodiment, the mass % of the total mass after the vitrification of the non-inspective glass D is 0 07 mass. The addition of NEUC1 was carried out in the same manner as in Example 3. From the above formula (2), the fluorine bubble growth start pressure pbg was 129 mmHg. The Pbg obtained here and the above formula (3) In the case where the reboiling pressure pr b is 48 mmHg, and the ambient gas pressure in the electric furnace is maintained at a pressure of Pr b of 48 mniHg or more, and the bubble growth start pressure Pbg is 129 mmHg or less, it is confirmed that it remains in the molten glass. The amount of bubbles is very small. On the other hand, when the ambient gas pressure of the electric furnace is maintained at a reboil pressure Prb of less than 48 mmHg, the amount of bubbles generated from the platinum plate in the molten glass is remarkably increased, so that the bubbles remaining in the molten glass can be confirmed. The amount is very large. (Example 9) Here, the results of experiments showing the validity of the formula (1) and the formula for the alkali-free glass A, B, and C' are shown in Tables 1 to 5 and Figs. 7 to 8. In the experiment, the β-OH value (nrnT1) and the chlorine content (mass 〇/〇) were changed for each glass composition to calculate the bubble growth starting pressure Pbg. Each of the glasses was placed in a quartz cell and placed in a molten glass of about 50 g' and melted at a predetermined temperature using an electric furnace having an observation window. After the glass is melted, the pressure is reduced to a desired pressure at a constant speed, and then the CCD camera is used to measure the change in the video bubble diameter under a certain pressure. After the end of the experiment, the change in the bubble diameter is analyzed to calculate the bubble growth start pressure Pbg. 28 201130760 Table 1 to Table 5 show the glass temperature, β-ΟΗ value (mnT1), gas content (% by mass), and experimental value (mmHg) of the bubble growth start pressure Pbg when the bubble is observed. 'The bubble growth start pressure pbg Calculated value of formula (1) or formula (2) (mmHg) 表 Table 3, in the case of alkali-free glass composition A, B and C, another 122J shows that the gas content (% by mass) is more than 0.12% by mass in 122 cases. Relevant individual results. Further, Tables 4 to 5 show the results of 41 cases in which the gas content (% by mass) was less than 12.12% by mass in the alkali-free glass compositions A, B, and C. In Fig. 7, the alkali-free glass compositions A, B, and C show that when the gas content (% by mass) is 0.12% by mass or more, the experimental value (mmHg) of the bubble growth start pressure pbg and the bubble growth start pressure Pb g Calculate the correlation of 122 points of the value (mmHg). In Fig. 8, the composition of the alkali-free glass composition A, B, and C, when the gas content (% by mass) is less than 12% by mass, the experimental value (mmHg) of the bubble growth start pressure Pbg and the bubble growth start pressure pb The correlation of the calculated value of g (mrnHg) of 41 points. The result of Fig. 7 is that the slope of the regression equation is 〇_92, and the square of the correlation coefficient is 〇·82 ′, which shows that the experimental value is appropriately estimated. The result of Fig. 8 is that the slope of the regression equation is 〇 97, and the square of the correlation coefficient is 〇 89, which shows that the experimental value is appropriately estimated by equation (2). It can be seen from the above that the equations (1) and (2) are effective in estimating the bubble growth start pressure Pbg. The same results were obtained by plotting the examples for the alkali-free glass D on the graphs of Figures 7 and 8. Further, although the glass temperatures at the time of observing the bubbles are shown in Tables 1 to 5, the glass temperatures at the time of bubble generation are not defined in the formulas (1) and (2) of the present month. This is considered to be because the clarification of the present invention is mainly related to the clarification of water, and the temperature dependence of the degree of melting of water is small.

S 29 201130760 Table 1

No Glass temperature at observation of bubbles (°c) β-ΟΗ Cl Pbg Experimental value (:丨)# Value A1 1450 0.331 0.194 313 299 A2 1500 0.331 0.194 315 299 A3 1550 0.331 0.194 351 299 A4 1450 0.291 0.207 289 275 A5 1500 0.291 0.207 295 275 A6 1550 0.291 0.207 311 275 A7 1450 0.265 0.152 222 221 A8 1500 0.265 0.152 240 221 A9 1550 0.265 0.152 258 221 A10 1450 0.352 0.192 324 314 A11 1500 0,352 0.192 350 314 A12 1550 0.352 0.192 368 314 A13 1450 0.351 0.185 319 309 A14 1500 0.351 0.185 345 309 A15 1550 0.351 0.185 360 309 A16 1400 0.301 0.19 307 273 A17 1400 0.323 0.176 317 282 A18 1400 0.328 0.173 330 284 A19 1400 0.279 0.187 253 253 A20 1400 0.278 0.186 255 252 A21 1400 0.275 0.187 251 250 A22 1425 0.279 0.187 261 253 A23 1425 0.278 0.186 260 252 A24 1425 0.275 0.187 261 250 A25 1400 0.32 0.203 304 295 A26 1450 0.331 0.194 304 299 A27 1450 0.331 0.194 320 299 A28 1450 0.331 0.194 317 299 A29 1450 0.292 0.209 298 277 A30 1450 0.292 0.209 298 277 A31 1450 0.292 0.209 301 277 A32 1400 0.28 0.197 266 260 A33 1400 0.272 0.197 275 254 A34 1400 0.272 0.19 275 250 A35 1400 0.282 0.199 285 263 A36 1400 0.293 0.189 274 266 A37 1400 0.348 0.201 348 316 A38 1400 0.389 0.176 340 334 A39 1400 0.389 0.176 343 334 A40 1350 0,333 0.188 283 297 A41 1350 0.336 0.186 283 298 A42 1350 0.321 0.186 280 286 A43 1375 0.335 0.189 315 299 A44 1375 0.336 0.186 320 298 A45 1375 0.321 0.186 290 286 A46 1400 0.341 0.183 317 300 A47 1400 0.293 0.176 262 258 A48 1425 0.293 0.176 274 258 A49 1400 0.28 0.174 243 246 A50 1425 0.28 0.174 260 246 A51 1450 0.306 0.203 308 284 A52 1450 0.306 0.203 306 284 A53 1450 0.306 0.203 346 284 A54 1450 0.29 0.203 288 272 A55 1450 0.278 0.215 285 269 30 201130760 Table 2

No Glass temperature when observing bubbles rc) β-ΟΗ Cl Pbs Experimental formula (l) Calculated value B1 1365 0.385 0.197 358 310 B2 1390 0.385 0.197 366 310 B3 1420 0.385 0.197 382 310 B4 1365 0.355 0.189 314 285 B5 1390 0.355 0.189 309 285 86 1420 0.355 0.189 322 285 B7 1365 0.283 0.186 255 234 B8 1390 0.283 0.186 252 234 B9 1420 0.283 0.186 281 234 B10 1365 0.319 0.192 277 262 B11 1390 0.319 0.192 276 262 B12 1420 0.319 0.192 294 262

S 31 201130760 Table 3

No Glass temperature at observation bubble (°c) iS-OH Cl Pta Experimental value (1) Calculated value C1 1365 0.312 0.205 286 255 C2 1420 0.312 0.205 280 255 C3 1365 0.368 0.185 328 276 C4 1420 0.368 0.185 322 276 C5 1365 0.238 0.275 264 256 C6 1420 0.238 0.275 277 256 C7 1365 0.245 0.213 245 218 C8 1365 0.245 0.213 229 218 C9 1365 0.245 0.213 202 218 CIO 1505 0.277 0.184 242 218 C11 1505 0.277 0.184 245 218 C12 1505 0.277 0.184 228 218 C13 1505 0.241 0.189 229 199 C14 1505 0.241 0.189 227 199 C15 1325 0.296 0,132 213 195 C16 1365 0.296 0.132 212 195 C17 1365 0.296 0.132 189 195 C18 1420 0.296 0.132 198 195 C19 1325 0.278 0.139 243 188 C20 1365 0.278 0.139 183 188 C21 1420 0.278 0.139 186 188 C22 1365 0.25 0.18 197 199 C23 1390 0.25 0.18 199 199 C24 1420 0.25 0.18 205 199 C25 1365 0.252 0.159 188 186 C26 1390 0.252 0.159 190 186 C27 1420 0.252 0.159 197 186 C28 1365 0.272 0.157 210 197 C29 1365 0.272 0.157 210 197 C30 1390 0.272 0'157 212 197 C31 1390 0.272 0,157 212 197 C32 14 20 0.272 0.157 222 197 C33 1420 0.272 0.157 214 197 C34 1390 0.275 0.153 200 196 C35 1390 0.271 0.16 211 198 C36 1390 0.271 0.16 209 198 C37 1390 0.268 0.159 206 196 C38 1390 0.268 0.159 204 196 C39 1390 0.271 0.156 199 196 C40 1390 0.271 0.156 195 196 C41 1390 0.27 0.162 201 199 C42 1330 0.27 0*162 205 199 C43 1360 0.27 0.162 194 199 C44 1330 0.273 0.158 210 198 C45 1360 0.273 0.158 211 198 C46 1390 0.273 0.158 206 198 C47 1365 0.313 0.146 261 215 C48 1390 0.313 0.14 268 215 C49 1420 0.313 0.146 272 215 C50 1365 0.392 0.194 337 297 C51 1390 0,392 0.194 352 297 C52 1420 0.392 0.194 370 297 C53 1365 0.371 0.145 279 251 C54 1390 0.371 0.145 276 251 C55 1420 0.371 0.145 370 251 32 201130760 Table 4

No : glass temperature when observing bubbles rc) β-ΟΗ Cl Ρ1) β experimental value (2) Calculated value Alb 1400 0.308 0.074 188 146 A2b 1450 0.308 0.074 153 146 A3b 1400 0.306 0.1 157 185 A4b 1450 0.306 0.1 162 185 A5b 1400 0.353 0.076 174 182 A6b 1450 0.353 0.076 191 182 A 7b 1400 0.37 0.073 176 189 A8b 1450 0.37 0.073 191 189 A9b 1400 0.643 0.048 376 345 A10b 1450 0.643 0Ό48 358 345 A11b 1400 0.681 0.039 369 358 A12b 1450 0.681 0.039 346 358 A13b 1400 0.597 0.101 369 394 A14b 1450 0.597 0.101 377 394 A15b 1400 0.604 0.11 367 413 A16b 1450 0.604 0.11 364 413 A17b 1400 0.522 0.122 428 373 A18b 1450 0.522 0.122 452 373 A19b 1375 0.506 0.128 426 371 A20b 1375 0.518 0.131 460 384 Table 5

No Glass temperature when observing bubbles Ct) β-ΟΗ Cl PbK experimental value (2) Calculated value B1b 1365 0.304 0.132 193 225 B2b 1390 0.304 0.132 199 225 B3b 1420 0.304 0.132 200 225 B4b 1365 0.328 0.121 213 226 B5b 1390 0.328 0.121 219 226 B6b 1420 0.328 0.121 215 226 B7b 1365 0.269 0.117 227 178 B8b 1390 0.269 0.117 205 178 B9b 1420 0.269 0.117 202 178 C1b 1365 0.373 0.113 253 245 C2b 1420 0.373 0.113 233 245 C3b 1365 0.387 0.094 252 228 C4b 1420 0.387 0.094 249 228 C5b 1365 0.248 0.118 150 161 C6b 1420 0.248 0.118 161 161 C7b 1365 0.395 0.092 248 231 C8b 1420 0.395 0.092 222 231 C9b 1325 0.254 0.118 180 165 C10b 1475 0,254 0.118 170 165 C11b 1325 0.406 0.115 263 272 C12b 1475 0.406 0.115 278 272 Industry According to the vacuum degassing method of the molten glass of the present invention, the pressure of the vacuum degassing 33 201130760 tank is maintained below the bubble growth start pressure pbg and maintained above the reboiling pressure Prb (mmHg). Therefore, the bubbles contained in the molten glass in the vacuum degassing tank are sufficiently grown, and can also be effectively The bubbles in the molten glass are removed, and on the other hand, the reboiling in the molten glass flowing into the vacuum degassing tank can be prevented, and as a result, the bubbles remaining in the molten glass after the vacuum degassing treatment can be extremely reduced, so that the production is extremely small. High-performance, high-quality glass with bubbles. As a result, a molten glass and a glass article having excellent bubble quality can be obtained, and in particular, an alkali-free glass substrate for FPD can be produced, which is quite useful. Further, the entire contents of the specification, the patent application, the drawings and the abstract of the patent application No. 2009-294230, filed on Dec. 25, 2009, are hereby incorporated by reference. BRIEF DESCRIPTION OF THE DRAWINGS 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. Figure 2 is a plot of the relationship between T2 and the coefficient a of equation (4) (pi〇t). Figure 3 is a graph plotting the relationship between D2 and the coefficient b of equation (4). Figure 4 is a graph plotting the relationship between D2 and the coefficient c of equation (5). Figure 5 is a graph plotting the relationship between T2 and the coefficient d of equation (5). Fig. 6 is a graph in which the relationship between the reboiling pressure Prb and the bubble growth start pressure pbg2 is plotted. 7 is an experimental value (mmHg) of the bubble growth start pressure Pbg and a bubble growth start pressure Pb g in the case where the chlorine content (% by mass) is 0.12% by mass or more. The relationship between the calculated values (mmHg) 34 201130760 The chart to be plotted. Fig. 8 shows the composition of the alkali-free glass A, B, and C. When the gas content (% by mass) is less than 0.12% by mass, the bubble growth start pressure Pbgi experimental value (Γηηιί^) and the bubble growth start pressure Pb g The calculated value (mmHg) is related to the graph of the drawing. [Explanation of main component symbols] 1···Decompression defoaming device ll···Reducing tank 12...Pressure degassing tank 13...Upward pipe 14...Down pipe 15...Insulation material 16...Attraction opening 20...Solution tank G··· molten glass

Pbg... bubble growth start pressure

Prb···reboil pressure T2...temperature a, b, c, d... coefficient

S 35

Claims (1)

201130760 VII. Scope of application for patents: L - Mi Rong _ 减 魏 财 魏 , , , , 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 魏 魏 魏 魏 魏 魏 魏 魏 魏 魏 魏 魏 魏 魏 魏 魏 魏 魏 魏The molten glass is an alkali-free glass; the method is to maintain the pressure in the vacuum degassing tank at the time of performing the vacuum degassing in the bubble growth of the molten glass represented by the following formula (1) or (2) The pressure Pbg (mmHg) or less is maintained at a reboil pressure Prb (mmHg) or more of the molten glass represented by the following formula (3); Pbg = (2.6082 X Τ 2-3538.2) χ [β-〇Η] + (-1.2102 χ T2+2612.2)x[C1]-80.3...(1); Pbg=(-0.2462 χ T2 + 1121.7) χ [β-ΟΗ]+(1.9714 x T2-1730.6)x[C1]-187.3. .....(2); Prb=〇.8325xPbg-59.5 (3); (wherein, T2 represents the viscosity of the molten glass at a temperature of l〇2dPa·s (.〇; [β -ΟΗ] represents the β-ΟΗ value of the alkali-free glass (mm·1); and [Cl] represents the chlorine content (% by mass) in the alkali-free glass; when [C1] is 0.12% by mass or more, the Pbg is of the formula (1) indicates that when [C1] is less than 0.12% by mass, Pbg is represented by formula (2) 2. The vacuum degassing method for molten glass according to item 1 of the patent application, wherein the above [0-〇拗 is 〇.15~〇.6!11111·1. 3. If the patent application range is 1 or 2 The vacuum degassing method of the molten glass of the present invention, wherein the aforementioned [C1] is from 0. 03 to 0.3 mass% / 〇. 4. The reduced pressure of the molten glass according to any one of claims 1 to 3, 2011. The defoaming method, wherein the butyl hydride is in the range of 1500 to 1750 ° C. The vacuum degassing method of the molten glass according to any one of claims 1 to 4, wherein the alkali-free glass is converted into the following oxides The mass % indicates that the following components are contained: Si02: 50 to 66 mass 0/〇; Al2〇3: 10.5 to 24% by mass; B2〇3: 0 to 12% by mass; MgO: 0 to 8% by mass; CaO: 0 ~ 14.5 mass%; SrO: 0 to 24 mass%; BaO: 0-13.5 mass%; and MgO+CaO+SrO+BaO: 9 to 29.5 mass%. 6. As in any of claims 1 to 4 The vacuum defoaming method of the molten glass according to the item, wherein the alkali-free glass is represented by mass% of the following oxides, and contains the following components: Si02: 58-66 Amount %; Al2〇3: 15 to 22% by mass; B2〇3: 0 to 12% by mass; MgO: 0 to 8% by mass; CaO: 0 to 9% by mass; SrO: 3 to 12.5% by mass; BaO: 0 ～2% by mass; and MgO+CaO+SrO+BaO: 9 to 18% by mass. 7. A method for producing a glass product, which has the following steps: S 37 201130760: a glass refining step, which melts the glass raw material and produces a molten glass; the vacuum degassing step is based on The method for forming a vacuum defoaming of molten glass according to any one of claims 1 to 6; and the step of forming a glass product by molding a molten glass which has been defoamed under reduced pressure. 38