WO2008029649A1 - Glass-making processes - Google Patents

Abstract

The invention provides a glass-making process of conducting vacuum defoaming without bumping; a glass-making process of conducting vacuum defoaming without making blisters remain in glass articles, which blisters result from the enlargement of a foam layer; and a glass-making process of conducting vacuum defoaming while inhibiting the vaporization of specific components (such as boron) contained in molten glass. A glass-making process which comprises the step of vacuum -defoaming molten glass in a vacuum defoaming tank, wherein the water vapor concentration of the atmospheric gas in the tank is controlled to be 60% by mole or below.

Description

 Specification

 Glass manufacturing method

 Technical field

 The present invention relates to a glass manufacturing method including a step of degassing a vacuum, a method of adjusting a water vapor concentration in an upper space in a vacuum degassing vessel, and a vacuum degassing device.

 Background art

 Conventionally, in order to improve the quality of a molded glass product, a clarification process for removing bubbles generated in the molten glass before forming the molten glass in which the raw material is melted in a melting furnace with a molding apparatus. Is being used.

 In this clarification process, molten glass is introduced into a reduced-pressure atmosphere, and bubbles in the molten glass flow that continuously flows under this reduced-pressure atmosphere are grown to increase the bubbles contained in the molten glass. There is known a vacuum degassing method in which a vacuum degassing method is performed, which is then removed from the vacuum atmosphere.

 [0003] And, in such a vacuum degassing method, in order to achieve suitable vacuum degassing conditions, a method that defines the pressure and temperature in the vacuum degassing tank has been proposed (Patent Document 1, Patent). Reference 2).

 Patent Document 1: Japanese Patent Laid-Open No. 2000-128422

 Patent Document 2: International Publication No. 02/098810 Pamphlet

 Disclosure of the invention

 Problems to be solved by the invention

[0004] Even if vacuum defoaming is performed under the preferred vacuum defoaming conditions as described above, for example, during the vacuum defoaming treatment, a foam layer that is usually present on the surface of the molten glass at about 10 mm or less is obtained. There was a case where so-called bumping occurred due to enlargement from 10 mm to several hundred mm. Bumping is a phenomenon in which bubbles that reach the glass surface that normally disappear with time exist stably for a long time by forming a layer without breaking, leading to an increase in the molten glass interface (molten glass surface). It is. As a result, there arises a problem that bubbles remain in the molten glass after vacuum degassing.

Even if bumping does not occur, as a result of the enlarged foam layer, bubbles remain in the glass product. In some cases, defects were caused.

 Further, for example, even if vacuum degassing is performed under the preferable vacuum degassing conditions as described above, specific components (boron and the like) in the molten glass are volatilized and the glass composition is changed. In some cases, the flatness of the base plate deteriorates.

[0005] An object of the present invention is to provide a glass manufacturing method for performing degassing under reduced pressure without causing bumping.

 It is another object of the present invention to provide a glass production method for depressurization and defoaming in which almost no bubbles remain in the glass product resulting from the enlargement of the foam layer.

 It is another object of the present invention to provide a glass production method for performing degassing under reduced pressure while suppressing volatilization of specific components (such as boron) in molten glass.

 Furthermore, a method of adjusting the water vapor concentration of the atmospheric gas in the vacuum degassing tank that can be preferably applied for such vacuum degassing, and the vacuum degassing of the molten glass capable of such vacuum degassing. It is to provide a foam device.

 Means for solving the problem

[0006] The present inventor has studied in detail the phenomenon in which the bubble layer on the surface of the molten glass in the vacuum degassing tank is enlarged, that is, the vacuum degassing treatment conditions when a so-called bumping occurs to cause a defect. And when the water vapor | steam density | concentration of the atmospheric gas in a vacuum degassing tank exceeded a specific value, it discovered that a bubble layer enlarged and many bubbles remain | survived in glassware. Further, it has been found that when the water vapor concentration exceeds another specific value higher than this specific value, the foam layer further enlarges and bumps, and more bubbles remain in the glass product. And a glass manufacturing method that performs vacuum degassing under reduced pressure defoaming conditions below these specific values, a vacuum degassing apparatus for molten glass that can be degassed under such conditions, and a pressure reduction of such an apparatus The present inventors have found that a method for adjusting the water vapor concentration of the atmospheric gas in the defoaming tank solves the above-mentioned problems, and has completed the present invention.

[0007] The present invention provides the following (1) to (8).

 (1) A glass production method comprising a step of depressurizing and defoaming molten glass by setting the water vapor concentration of the atmospheric gas in the vacuum degassing tank to 60 mol% or less.

(2) By introducing a low moisture gas into the atmosphere gas of the vacuum degassing tank, the atmosphere The glass production method according to (1), wherein the water vapor concentration of the gas is 60 mol% or less.

 (3) The glass production method according to (1) or (2), wherein the atmospheric gas has a water vapor concentration of 30 mol% or less.

 (4) The method for producing glass according to (2) or (3) above, wherein the oxygen concentration (volume%) of the low moisture gas is lower than the oxygen concentration (volume%) in the air.

 (5) The glass production method according to (4), wherein the oxygen concentration (volume%) of the low moisture gas is 15 volume% or less.

 (6) Measure the water vapor concentration of the atmospheric gas in the vacuum degassing tank for vacuum degassing of the molten glass and, based on the measurement result of the water vapor concentration, move to the atmospheric gas in the vacuum degassing tank. A glass manufacturing method in which the water vapor concentration of the atmospheric gas in the vacuum degassing tank is adjusted to 60 mol% or less by introducing.

 (7) A decompression housing to be sucked under reduced pressure, a decompression deaeration tank provided in the decompression housing for decompressing defoaming of the molten glass, and provided in communication with the decompression defoaming tank, Molten glass having introduction means for introducing the molten glass into the vacuum degassing tank and lead-out means provided in communication with the vacuum degassing tank and for deriving the molten glass after vacuum degassing from the vacuum degassing tank A degassing apparatus comprising: a water vapor concentration measuring means for measuring a water vapor concentration of the atmospheric gas in the vacuum degassing tank; and a low moisture gas for introducing a low moisture gas into an upper space inside the vacuum degassing tank. Vacuum degassing apparatus for molten glass further comprising gas introduction means

(8) A water vapor concentration control means that can control the water vapor concentration of the atmospheric gas to a desired value in the vacuum degassing apparatus, and a gas that controls the amount of low moisture gas introduced by a signal from the control means The vacuum degassing apparatus according to (7), further comprising an amount control unit.

(9) The vacuum degassing apparatus for molten glass according to (7) or (8), wherein the low moisture gas introducing means is provided upstream of the vacuum degassing tank.

The invention's effect

The glass production method of the present invention comprises a step of degassing the molten glass under reduced pressure by setting the water vapor concentration of the atmospheric gas in the vacuum degassing tank to 60 mol% or less, and thereby the vacuum degassing of the molten glass without causing bumping. The effect that foam can be performed is produced. And made of glass The product has the effect of not causing defects caused by bubbles remaining due to bumping. Moreover, since the glass manufacturing method of this invention can prevent bumping, glass manufacturing can be continued stably.

 This “stable manufacturing” is a very important factor in quality control for glass manufacturing equipment that operates day and night. This is because once the quality deteriorates, it is necessary to shut down the equipment for repair and adjustment. In addition, it is possible to suppress deposits from adhering to the walls and ceiling of the depressurization defoaming tank from the bumped molten glass, so it is possible to suppress the formation of defects in the glass product due to the fall and improve the quality. .

 In addition, since the glass manufacturing method of the present invention reduces moisture in the atmosphere that promotes volatilization of specific components (boron, etc.), it suppresses volatilization of specific components (boron, etc.) in molten glass. There is an effect that can be. And when a glass base plate is manufactured, the deterioration of the flatness can be suppressed. In particular, display glass such as liquid crystal glass is strictly regulated in terms of composition, while boron is very volatile, so boron content is rigorously adjusted. There is a need to. Therefore, according to the glass manufacturing method of this invention, it is possible to manufacture efficiently the glass which has the composition and flatness within a specification range.

 [0009] In the glass production method of the present invention, the water vapor concentration is preferably 30 mol% or less. As a result, in addition to preventing the occurrence of bumping as described above, the foam layer is prevented from being enlarged, and thus it is possible to suppress the occurrence of many defects in the glass product (specifically, per unit mass of the glass product). 0.5 bubbles / kg or less).

 [0010] In addition, the vacuum degassing apparatus of the present invention can provide a vacuum degassing apparatus suitable for performing the glass manufacturing method of the present invention.

 Brief Description of Drawings

 FIG. 1 is a diagram showing an example of the configuration of a vacuum degassing apparatus according to the present invention.

 FIG. 2 is a view showing a vacuum degassing apparatus and the like according to the present invention.

 FIG. 3 is a diagram showing the results of Example 1 of the present invention.

 FIG. 4 is a diagram showing the results of Example 3 of the present invention.

Explanation of symbols [0012] 1 Vacuum degassing device

 3 Atmospheric gas

 3 Exhausted atmospheric gas

 5 Upper space

 6 opening

 7 Low moisture gas

 8 opening

 9 opening

 10 Vacuum deaerator

 11 Depressurization

 12 Vacuum degassing tank

 13 Rise pipe

 14 Downcomer

 15 Insulation

 20 Dissolution tank

 22 Upstream pit

 24 Downstream pit

 28

 30 Means for measuring water vapor concentration

 40 Low moisture gas introduction means

 41 Low moisture gas generator

 42 Flow control valve

 44 Flow meter

 G melting glass

 BEST MODE FOR CARRYING OUT THE INVENTION

 [0013] The glass production method of the present invention will be described.

The glass production method of the present invention comprises a step of defoaming molten glass under a reduced pressure defoaming tank atmosphere gas concentration of 60 mol% or less (hereinafter referred to as “the depressurization defoaming step of the present invention”). . ). And, it is preferable to have a raw material melting step as a pre-process, and it is preferable to have a molding step as a post-process! /. These raw material melting step and molding step are not particularly limited, and may be, for example, a conventionally known step. In addition to these steps, other processes may be provided.

 In the present invention, “atmosphere gas” means an atmosphere gas that fills the space above the molten glass (upper space) inside the vacuum degassing vessel.

 [0014] In the glass production method of the present invention, the reduced-pressure defoaming step of the present invention is a step of defoaming bubbles in the molten glass by flowing the molten glass into a reduced-pressure defoaming tank having a reduced pressure inside. However, there is no particular limitation as long as it is a step of degassing under reduced pressure with the water vapor concentration of the atmospheric gas in the vacuum degassing tank being 60 mol% or less!

 For example, by measuring the water vapor concentration of the atmospheric gas in the vacuum degassing tank in the vacuum degassing device, and introducing the low moisture gas described later into the upper space based on the measurement result of the water vapor concentration, this vacuum degassing device Applying a method for adjusting the water vapor concentration of the atmospheric gas in the vacuum degassing tank (hereinafter also referred to as “moisture adjustment method of the present invention”), the water vapor concentration of the atmospheric gas is 60 mol% or less. The reduced-pressure defoaming step of the present invention can be performed. The low moisture gas may be introduced continuously or intermittently.

 [0015] The vacuum degassing step of the present invention to which the moisture adjustment method of the present invention is applied can be performed using, for example, the vacuum degassing apparatus of the present invention.

 [0016] The vacuum degassing apparatus of the present invention will be described.

 The vacuum degassing apparatus according to the present invention is a vacuum degassing apparatus for degassing molten glass under reduced pressure, wherein the molten glass is allowed to flow inside the reduced pressure state to degas bubbles in the molten glass. A tank, a water vapor concentration measuring means for measuring the water vapor concentration of the atmospheric gas in the vacuum degassing tank, and a low moisture gas introducing means for introducing a low moisture gas into the upper space. A vacuum degassing apparatus capable of reducing the water vapor concentration and degassing the molten glass under reduced pressure, such as the vacuum degassing apparatus shown in FIG.

[0017] Referring to FIG. FIG. 1 is a view showing a vacuum degassing apparatus 1 which is an example of the configuration of the vacuum degassing apparatus of the present invention. The vacuum degassing tank 12 and the water vapor concentration measuring means 30 included in the vacuum degassing apparatus of the present invention Show low moisture gas introduction means 40! [0018] First, the vacuum degassing tank 12 will be described with reference to FIG. FIG. 2 is a diagram (sectional view) illustrating a vacuum degassing apparatus 10 of the present invention including a vacuum degassing tank 12 (the water vapor concentration measuring means and the low moisture gas introducing means are not described).

 In the vacuum degassing apparatus 10 shown in FIG. 2, the cylindrical vacuum degassing tank 12 is housed and arranged in the vacuum housing 11 so that its long axis is oriented in the horizontal direction. A rising pipe 13 oriented in the vertical direction is attached to the lower surface of one end of the vacuum degassing tank 12, and a lowering pipe 14 is attached to the lower surface of the other end. A part of the ascending pipe 13 and the descending pipe 14 is located in the decompression housing 11.

 [0020] And, the upper surface of the vacuum degassing tank 12 has a plurality of openings. Through at least one opening 6, the low moisture gas 7 is passed from the outside of the vacuum housing 11 to the upper space 5 inside the vacuum degassing tank 12. Introducing power S. An opening 8 formed in the decompression housing 11 is connected to decompression means such as a pump (not shown in FIG. 2; shown as pump 28 in FIG. 1), and is an atmospheric gas 3 that fills the upper space 5 3 Can be discharged to the outside of the vacuum housing 11 (the discharged gas is denoted as atmospheric gas; T), and the pressure inside the vacuum degassing tank 12 can be reduced. Note that the locations of the opening 6 and the opening 8 are not limited to the locations indicated by the opening 6 and the opening 8 in FIG. 2! /, But the opening 6 is on the upstream side of the vacuum degassing tank 12, and the opening 8 is on the downstream side thereof. It ’s better to have it on each side! /,. By providing the opening 6 constituting a part of the low moisture gas introduction means upstream of the vacuum degassing tank 12, the low moisture gas 7 introduced from the opening 6 into the upper space 5 inside the vacuum degassing tank 12 is reduced. The ability to flow from the upstream side of the vacuum degassing tank 12 toward the downstream side where the opening 8 is provided to make the upper space 5 inside the vacuum degassing tank 12 into an atmospheric gas with a uniform low water vapor concentration. S can.

 Further, for example, a known pressure gauge and thermometer capable of measuring the pressure (P) and temperature (T) of the atmospheric gas 3 are installed in the vacuum degassing tank 12 (not shown).

Further, as shown in FIG. 2, the riser 13 communicates with the vacuum degassing tank 12 and is an introducing means for introducing the molten glass G from the melting tank 20 into the vacuum degassing tank 12. For this reason, the lower end portion of the ascending pipe 13 is fitted into the open end of the upstream pit 22 and is immersed in the molten glass G in the upstream pit 22.

The downcomer pipe 14 communicates with the vacuum degassing tank 12 to depressurize the molten glass G after the vacuum degassing. It is a derivation means that descends from the bubble tank 12 and leads to a processing tank (not shown) in a subsequent process. For this reason, the lower end portion of the downcomer pipe 14 is fitted into the open end of the downstream pit 24 and immersed in the molten glass G in the downstream pit 24.

 In the decompression housing 11, a heat insulating material 15 such as a heat insulating brick is provided around the decompression defoaming tank 12, the riser pipe 13, and the downcomer pipe 14 to insulate them.

In the vacuum degassing apparatus 10 shown in FIG. 2, since the vacuum degassing tank 12, the rising pipe 13 and the lowering pipe 14 are conduits for the molten glass G, a material having excellent heat resistance and corrosion resistance to the molten glass is used. It is made using. An example is a hollow tube made of platinum or a platinum alloy. Specific examples of the platinum alloy include a platinum gold alloy and a platinum rhodium alloy. Another example is a hollow tube made of a ceramic non-metallic inorganic material, that is, a dense refractory. Specific examples of the dense refractory include, for example, electric refractories such as alumina electric refractories, dinoleconia electric refractories, alumina-dinoleconia-silica electric refractories, and dense alumina refractories. Dense zirconia silica refractories and dense alumina zirconia silica refractories such as refractories.

 [0023] The dimensions of each component of the vacuum degassing apparatus 10 can be appropriately selected as necessary. The dimensions of the vacuum degassing tank 12 should be appropriately selected according to the vacuum degassing apparatus to be used, regardless of whether the vacuum degassing tank 12 is made of platinum, platinum alloy, or dense refractory. Power S can be. In the case of the vacuum degassing tank 12 shown in FIG. 2, specific examples of the dimensions are as follows.

 Horizontal length ::! ~ 20m

 Inner diameter: 0.2 to 3m (circular cross section)

 When the vacuum degassing tank 12 is made of platinum or a platinum alloy, the wall thickness is preferably 4 mm or less, more preferably 0.5 to 1.2 mm.

[0024] The decompression housing 11 is made of metal, for example, stainless steel, and has a shape and dimensions that can accommodate a decompression deaeration tank.

The riser pipe 13 and the downfall pipe 14 can be appropriately selected according to the vacuum degassing apparatus to be used regardless of the force made of platinum, platinum alloy, or dense refractory. For example The dimensions of the ascending pipe 13 and the descending pipe 14 can be configured as follows. Inner diameter: 0.05—0.8 m, more preferably 0.1—0.6 m

 Length: 0.26m, more preferably 0.44m

 When the riser 13 and the downcomer 14 are made of platinum or a platinum alloy, the wall thickness is preferably 0.45 mm, more preferably 0.84 mm.

[0025] The vacuum degassing tank of the vacuum degassing apparatus of the present invention is, for example, the vacuum degassing tank 12 having such a configuration.

 Next, the water vapor concentration measuring means 30 included in the vacuum degassing apparatus of the present invention will be described. In FIG. 1, the water vapor concentration measuring means 30 is connected to the downstream side of the vacuum degassing tank 12 by piping or the like. A pump 28 as decompression means is connected to the downstream side. By this pump 28, the atmospheric gas discharged from the vacuum degassing tank 12; T can be sent S. Atmospheric gas 3 'discharged from pump 28 is released to the atmosphere after purification if necessary.

[0027] The water vapor concentration measuring means 30 may be a commercially available dew point meter, or a measuring means for measuring the pressure, temperature, gas flow rate and the like of the atmospheric gas 3 'discharged from the vacuum degassing tank 12. It may be. As each measuring means, for example, a conventionally known pressure gauge, thermometer, and gas flow meter can be used. The water vapor concentration is a value representing the amount of water vapor contained in the entire atmospheric gas.

Then, the water vapor concentration (C) [mol%] of the atmospheric gas 3 ′ may be measured using a commercially available dew point meter, or alternatively, the water contained in the atmospheric gas; W) It can also be estimated by measuring [g]. For example, the atmospheric gas discharged from the vacuum degassing layer 12; the gas flow rate of T is F [m ³ / h], the gas outflow time is t [h], and the water vapor concentration measuring means 3

 out out

 When the pressure and temperature of the atmospheric gas 3 ′ measured at 0 are P [Pa] and T [K],

 twenty two

 The water vapor concentration (C) [mol%] in the atmospheric gas 3 ′ is expressed by the following equation (1).

By setting the water vapor concentration calculated by Equation (1) to 60 mol% or less, the molten glass can be defoamed under reduced pressure without causing bumping, and bubbles are generated due to remaining bubbles in the glass product. Do not cause the defect! / ,! [0028] country

C =-~~ ^ -x lOO... Formula ( ₁ )

[0029] Each unit is as follows.

C: mol% W: g T: KP: Pa F: m ³ / ht: h R (gas constant): J 'K / mol

 2 2 out out

 Next, the low moisture gas introduction means 40 of the reduced pressure degassing apparatus of the present invention will be described. In FIG. 1, the low moisture gas introduction means 40 is connected to the upstream side of the reduced pressure defoaming tank 12 by piping or the like. . Then, through this pipe or the like, it is possible to introduce the low moisture gas 7 from the low moisture gas introduction means 40 with the force S.

 For example, as shown in FIG. 1, the low moisture gas introduction means 40 includes a low moisture gas generator 41 and a depressurized defoaming tank 12 connected by a pipe or the like. Water gas 7 can be introduced into the upper space 5 of the vacuum degassing tank 12. A flow control valve 42 and a flow meter 44 are provided in this order between the low moisture gas generating device 41 and the vacuum degassing tank 12, and the introduction amount of the low moisture gas 7 can be adjusted with these. it can.

 The arrangement of the flow control valve 42 and the flow meter 44 may be reversed! /.

 [0031] Here, the low moisture gas introduction means 40 may include introduction means (for example, a high pressure fan) for actively introducing the low moisture gas 7 into the upper space 5 of the vacuum degassing tank 12. Good. In this case, the upper space 5 and the low moisture gas 7 can be efficiently introduced, which is preferable.

 [0032] If the atmosphere is used as the low moisture gas 7, the low moisture gas generator described above is used.

 41 is not necessary. For example, it is only necessary to introduce the upper space 5 in which one end of a pipe connected to the upper space 5 is opened to the atmosphere by opening and closing the flow control valve 42 and the atmosphere is decompressed through this pipe.

 In addition, when an inert gas other than the atmosphere, for example, is used as the low moisture gas 7, the above-mentioned water vapor concentration measuring means 30 can measure the gas component of the atmospheric gas 3 'discharged from the upper space 5. Having a component measuring instrument!

[0033] In the present invention, the low moisture gas is a moisture content higher than the atmospheric gas 3 in the upper space 5.

It means gas with low (water vapor concentration). Low moisture gases include air, dry air, N, Examples thereof include an inert gas such as Ar, and there may be a plurality of types as well as one type. The water vapor concentration of the low moisture gas is preferably 0 to 20 mol%, more preferably 0 to 5 mol%, still more preferably O to lmol%. The water vapor concentration of the low moisture gas can be measured using a commercially available outdoor meter.

The vacuum degassing apparatus of the present invention is, for example, a vacuum degassing apparatus 1 having such a vacuum degassing tank 12, a water vapor concentration measuring means 30, and a low moisture gas introduction means 40.

 In such a vacuum degassing apparatus of the present invention, when the water vapor concentration of the atmospheric gas in the upper space is measured by the water vapor concentration measuring means and becomes higher than the desired water vapor concentration, the low moisture gas introducing means lowers the moisture content. When the gas is introduced! /, The water vapor concentration of the atmospheric gas in the upper space can be adjusted to a desired concentration by repeating the adjustment as appropriate.

 For example, the water vapor concentration (C) obtained by the above equation (1) and the target water vapor concentration (C) have the relationship of the following equation (2), so the amount of low moisture gas introduced into the upper space ( F) and lead

 in

 Input time (t), discharge amount of atmospheric gas from the upper space (F) and discharge time (t),

 In OUT OUT and by adjusting the water vapor concentration (S) [mol%] of the low-moisture gas, the force S is used to adjust the water vapor concentration to the target level.

[0035] [Equation 2]

• Formula (2)

[0036] The meaning and unit of each symbol are as follows.

C: [mol%], V (volume of the upper space): [m ³ ], V: [m ³ ], V: [m ³ ]

 1 in out

[0037] where V is the introduced gas volume (FX t) [m ³ ] obtained from the introduced amount (F [m ³ / h]) measured by the flow meter 44 and the introduced time (t [h]). The amount of conversion at the temperature and pressure of the upper space of

 in in

 The Similarly, V is the amount of emissions measured by the flow meter included in the water vapor concentration measuring means 30 (

 out

F [m ³ / h]) and the exhaust gas volume (FX t) [m ³ ] obtained from the exhaust time (t [h]) is a conversion amount in the temperature and pressure of the out space.

 In order to keep the pressure in the upper space constant, it is necessary to set V = v.

 m out

[0038] For example, water vapor concentration (C) = 20mol% in the upper space with volume (V) = lm ³ is the target In order to reduce the water vapor concentration (C) = 10 mol%, when V = V, the introduction of low moisture gas

 1 in out

Input (V) = 0.53m ³

 in

 Therefore, when the temperature of the upper space (T) = 1673K and the pressure (P) = 25kPa, the temperature of the introduced gas at the position of the flow meter 44 (T) = 298K and the pressure (P) = 101kPa, the introduced gas

 3 3

The volume X t) is 0 · 023 [m ³ ].

 in in

 In practice, moisture evaporation from molten glass and equipment components, or changes in water vapor concentration due to leak gas occur, so adjustments must be made constantly.

[0039] During the production of glass products, it is preferable to constantly monitor and control the water vapor concentration. Specifically, it is preferable that the vacuum degassing apparatus has a water vapor concentration control unit capable of controlling the water vapor concentration of the atmospheric gas to a desired value, based on a signal from the control unit. It is preferable to further have a gas amount control means for controlling the amount of gas introduced.

 For example, T, P, F, t, W, S, F, and t are measured constantly and their data are

 2 2 OUT OUT 2 IN IN

 It is preferable that the vacuum degassing apparatus of the present invention has a water vapor concentration control means that can control the water vapor concentration of the upper space to a desired value by the computer. Further, it is preferable that the vacuum degassing apparatus of the present invention has a gas amount control means for enabling the computer to control the opening and closing of the flow rate control valve 42 and feeding back the data of the flow meter 44 to the computer. Furthermore, in order to keep the production performance constant, it is desirable to adjust the flow rate while controlling to a desired pressure.

 [0040] The glass production method of the present invention is preferably carried out using such a vacuum degassing apparatus of the present invention, but other methods may be applied. For example, when it is not necessary to introduce gas into the upper space in the depressurization defoaming tank as in the depressurization defoaming apparatus of the present invention, the atmosphere in the depressurization defoaming tank is connected to the atmosphere in the depressurization tank and hooding. The water vapor concentration of the gas in the decompression housing may be reduced.

[0041] In the glass production method of the present invention, the vacuum degassing treatment conditions are not particularly limited as long as they are within a normal range. The normal pressure treatment conditions are: the atmospheric gas pressure (P) in the upper space inside the vacuum degassing tank is 38 to 460 mmHg (5;! To 613 hPa), and the temperature (T) is 110 ° C to 1500 ° C, especially 1250 ° C ~; treatment conditions for vacuum degassing at 1450 ° C. [0042] In the vacuum degassing step of the present invention included in the glass manufacturing method of the present invention, the water vapor concentration of the atmospheric gas inside the vacuum degassing tank is set to 60 mol% or less. Then, the bubbles in the molten glass can be degassed under reduced pressure conditions without causing so-called bumping! /.

 In addition, since the bubble layer tends to be thinner as the water vapor concentration is lower, the water vapor concentration of the atmospheric gas inside the vacuum degassing tank is preferably 50 mol% or less, more preferably 40 mol% or less. preferable. A water vapor concentration of 30 mol% or less is preferable because the foam layer tends to be thinner. Also, depending on the glass composition, each bubble may shrink or break, which is preferable because the foam layer becomes thinner. Furthermore, it is preferable because bubbles of a size that can be regarded as a defect in a glass product hardly remain. If the water vapor concentration is lower, the probability of defects occurring in the glass product is further reduced. Therefore, it is more preferable that it is 25 mol% or less, more preferably 20 mol% or less, and more preferably 15mo 1% or less. More preferably, it is more than S, more preferably 10 mol% or less, and even more preferably 5 mol% or less.

 [0043] Further, in addition to the above, the present inventors have found that such bubble shrinkage is a phenomenon that is particularly prominent in molten glass having a specific composition.

 Specifically, when the molten glass is a polysilicate glass, the bubbles tend to remarkably shrink when the water vapor concentration is 30 mol% or less. Therefore, the glass production method of the present invention, the vacuum degassing apparatus of the present invention, and the moisture adjustment method of the present invention can be preferably used in the case of producing a polysilicate glass.

 [0044] Here! /, The polysilicate glass has the following composition, for example.

 Composition range: SiO: 55 to 74, Al 2 O: 10 to 20, B 2 O: 5 to; 12 Al 2 O / B 2 O: 1.5

 2 2 3 2 3 2 3 2 3

-3, MgO: 0-5, CaO: 0-5, SrO: 0-; 12, BaO: 0-; 12, SrO + BaO: 6-12 (unit: mass%).

[0045] In the past, there has been no study on the force / water vapor concentration in which the preferred pressure and temperature conditions in the vacuum degassing tank were presented. The present inventor has eagerly investigated the cause of sudden boiling or enlargement of the foam layer even when defoaming under the reduced-pressure defoaming conditions presented in the past. We found that such a problem can be solved by paying attention. [0046] Further, the present inventor has also found out that volatilization of a specific component (such as boron) in the molten glass can be suppressed by setting the water vapor concentration to 60 mol% or less. By suppressing volatilization of components such as boron, it is possible to prevent variations in composition of boron and the like, and it is possible to suppress deterioration in flatness due to composition variations.

 In addition, the volatilization of the volatile components such as Cl, F, and S can be suppressed, so that the composition fluctuation of these components can be prevented and the deterioration of the flatness caused by the composition fluctuation can be suppressed. can do.

 These components such as Cl, F, and S are considered to be greatly affected by moisture volatilization. For example, F is considered to volatilize as HF and S as H 2 SO. Therefore, decompression release

 twenty four

 By setting the water concentration in the foam tank to a certain level or less, it is considered that fluctuations in the above components that volatilize with the volatilization of water can be suppressed.

 In addition, there are very detailed specifications for the characteristics of glass depending on the application, and the composition of the glass is determined in great detail to meet the specifications. For example, there is naturally a standard for the content of boron. In the conventional method, since boron is volatilized, it is necessary to use more boron as a raw material. Conventionally, the amount of volatilization of boron varies depending on the conditions, and in some cases, the boron content may be out of specification. In the present invention, such problems are solved and useful.

 Also from this point, the glass production method of the present invention, the vacuum degassing apparatus of the present invention, and the water content adjustment method of the present invention are not limited to ordinary glass, and are preferably used particularly when producing a polysilicate glass. If you can do it, yeah

[0047] Further, in the present invention, the low moisture gas introduced into the upper space inside the vacuum degassing tank is preferably a gas having an oxygen concentration lower than the oxygen concentration in the air. The oxygen concentration is preferably 15% by volume or less, more preferably 10% by volume or less, and even more preferably 5% by volume or less. The low moisture gas is preferably a gas not containing oxygen, such as N gas, Ar gas, CO, or the like.

 twenty two

When the oxygen concentration of the low moisture gas introduced into the upper space is such a value, in addition to the thinning of the foam layer as described above, platinum or a platinum alloy is used as the material of the vacuum degassing tank. In this case, the oxidation of the platinum is suppressed, the life of the vacuum degassing tank is extended, and further, the generation of defects derived from platinum in the glass product can be suppressed.

[0048] As described above, the glass manufacturing method of the present invention preferably includes the vacuum degassing step of the present invention, and preferably includes a raw material melting step and a molding step as a pre-process and a post-process. This raw material melting step is, for example, a conventionally known one, for example, a step of melting the raw material by heating to about 1400 ° C. or higher according to the type of glass. The raw material to be used is not particularly limited as long as it is compatible with the glass to be produced. For example, it is possible to use raw materials prepared by mixing conventionally known materials such as cinnabar, boric acid and limestone according to the composition of the final glass product. it can. This raw material may contain the desired fining agent. The molding step may be a conventionally known one, for example, a float molding step, a roll-out molding step, a fusion molding step, or the like.

 Example

 Hereinafter, the present invention will be specifically described based on examples. However, the present invention is not limited to this.

 <Example 1>

 In order to reproduce the atmosphere in which vacuum degassing was performed, a platinum crucible containing glass raw materials was placed in a vacuum vacuum container. The crucible was heated to melt the glass, and the temperature of the molten glass was adjusted to 1420 ° C. Thereafter, the absolute pressure in the vacuum decompression vessel was set to 26.7 kPa. Here, the composition of the glass raw material used is as follows.

 SiO: 59.4%, Al 2 O: 17.6%, B 2 O: 7.9%, MgO: 3.2%, CaO: 3.7%, Sr

 2 2 3 2 3

 0: 7.9%, BaO: 0.1%

 The examples;! To 3 are the same as those shown in FIG. 1 except that the vacuum defoaming tank 12 shown in FIG. 1 was replaced by a platinum crucible containing molten glass. It can be regarded as equivalent to the result of the vacuum degassing tank 12 in this case.

[0050] Next, air adjusted to a desired water vapor concentration was introduced into the vacuum decompression vessel, and the water vapor concentration (mol%) of the atmosphere in the vacuum decompression vessel was changed to various values for adjustment. For each water vapor concentration, the bubbles in the molten glass were photographed using a CCD camera from a viewing window provided in the vacuum decompressor. And after 30 minutes, molten glass in the crucible Was rapidly cooled and solidified, and the number of bubbles (counting those with a diameter of 100 m or more) present in the solidified sample was measured to obtain the bubble density (pieces / kg). Here, the mass of the molten glass was 5. Okg, and the number of bubbles in the glass before decompression was almost the same for each water vapor concentration.

 The results are shown in Figure 3.

 [0051] From FIG. 3, it can be confirmed that bubbles remain as the water vapor concentration in the atmosphere in the vacuum decompression vessel increases. In Fig. 3, the horizontal axis represents the water vapor (moisture) concentration of the atmosphere, and the vertical axis represents the number of bubbles in Log!

 When the water vapor concentration was more than 60 mol%, the molten glass interface rose rapidly while observing with a CCD camera, and V, a so-called bumping phenomenon occurred.

<Example 2>

 Next, using the same apparatus as in Example 1, the thickness of the foam layer was measured with the water vapor concentration of the atmosphere in the vacuum decompression vessel set to 70 mol%, 47 mol%, 31 mol%, and 3 mol%. Furthermore, in Example 1, the low moisture gas, which was air, was changed to N, CO, Ar, and the atmosphere in the vacuum decompression vessel.

 twenty two

 A similar test was conducted with the ambient water vapor concentration being less than lmol%. The glass composition is the same as in Example 1.

 The results are shown in Table 1.

[0053] [Table 1] Table 1

[0054] As described above, when the water vapor concentration is 70 mol%, the thickness of the foam layer becomes 20 mm or more. We were able to confirm the power to loosely bump. When the water vapor concentration was 3 to 47 mol%, a foam layer having a thickness of about! To 2 mm was formed, but no bumping was confirmed. Furthermore, when the atmosphere was N, CO or Ar (water vapor concentration was less than lmol%), no foam layer was formed. Up

 twenty two

 From the above results, the water vapor concentration should be 60 mol% or less. The thickness of the foam layer is 1

It is preferable to be about 5mm or less!

<Example 3>

 In the same test as in Example 2, the shrinkage rate of bubbles in the foam layer was measured for each type of atmosphere. Here, the same porosilicate glass as in Example 1 was used as the molten glass. The results are shown in Fig. 4. In FIG. 4, the bubble diameter is a normalized value. Normalization is the ratio of the bubble diameter at each time to the bubble diameter when the bubbles inside the molten glass rise and reach the bubble layer. Therefore, the time when the bubble reaches the bubble layer is the elapsed time Os, and the bubble diameter at that time is 1.0.

[0056] From FIG. 4, it is clear that air bubbles contract in the atmosphere with a water vapor concentration of 3 mol% and with N, CO, or Ar with a water vapor concentration of 1 mol% or less compared to the air with a water vapor concentration of 31 mol%.

 twenty two

 The speed got faster.

 From this result, it was found that the lower the water vapor concentration in the atmosphere, the easier the bubbles to shrink, that is, the bubbles easily disappear.

 <Example 4>

 Next, the state of bubbles rising to the surface of the molten glass by vacuum defoaming treatment and then breaking and disappearing was determined using various atmospheric water vapor concentrations (lmol%, 9mol%, 13mol%, 19mol%, 22mol%, 35mol%, 70 mol%) and glass composition (soda lime glass: composition A, composition B, composition C). Here, a 50cc transparent quartz glass beaker was used as a container so that the state of the foam could be observed, and the thickness of the foam layer when about 50 g of glass was melted was measured. In addition, the number of bubbles that floated on the surface of the molten glass (B) and reached the surface of the molten glass

 S

 Bubbles-The number of bubbles that disappeared (B) was observed with a CCD camera and counted, and the bubble breakage rate (B / B

 B B S

 %) Was calculated. The thickness of the foam layer (mm) and the bubble breaking rate (%) are shown in Table 2 below.

[0058] In all cases, the temperature of the molten glass was heated to 1200 ° C. The absolute pressure in the container is 18.7 kPa for composition A, 10.3 kPa for composition B, and 14 for composition C. 4 kPa. The content of each component in Composition A, Composition B, and Composition C was as shown in Table 3 below. In Table 3, “%” indicates mass%.

[0059] [Table 2]

 Table 2

[0060] [Table 3]

 Table 3

表 2から、容器内の雰囲気の水蒸気濃度が高いほど破泡率が低ぐ気泡が残存す ることを確認できる。具体的には、雰囲気の水蒸気濃度が 60mol%を超えると泡層が 20mm以上の厚さとなる力 60mol%以下であると泡層が薄くなることが確認できる。 なお、水蒸気濃度が 60mol%超の場合は、 CCDカメラで観察している際に溶融ガラ ス界面が急激に上昇し、いわゆる突沸現象が生じた。また、容器内の雰囲気の水蒸 気濃度が 15mol%未満の場合、破泡率が高くなり、好ましいことが分かった。すなわ ち、容器内の雰囲気の水蒸気濃度が 60mol%以下であると突沸現象を防止でき泡 層を薄くすることができるとともに、前記水蒸気濃度をさらに低くすると破泡率が高くな り泡が消滅することが判明した。

From Table 2, it can be confirmed that bubbles with a lower bubble breaking rate remain as the water vapor concentration in the atmosphere in the container increases. Specifically, it can be confirmed that if the water vapor concentration in the atmosphere exceeds 60 mol%, the foam layer becomes thin when the force is 60 mol% or less, which gives the foam layer a thickness of 20 mm or more. When the water vapor concentration was over 60 mol%, the melting glass interface rose rapidly during observation with a CCD camera, and so-called bumping phenomenon occurred. In addition, steaming the atmosphere in the container It was found that when the gas concentration is less than 15 mol%, the bubble breaking rate is high, which is preferable. In other words, if the water vapor concentration in the atmosphere in the container is 60 mol% or less, the bumping phenomenon can be prevented and the foam layer can be made thinner, and if the water vapor concentration is further reduced, the bubble breaking rate increases and the bubbles disappear. Turned out to be.

Industrial applicability

 INDUSTRIAL APPLICABILITY The present invention can be applied to a glass manufacturing method including a vacuum degassing apparatus and a vacuum degassing process for molten glass, and is particularly suitable for manufacturing high-quality display glass with few bubbles. It should be noted that the entire contents of the specification, claims, drawings and abstract of Japanese Patent Application No. 2006-233441, filed on August 30, 2006, are hereby incorporated herein by reference. As it is incorporated.

Claims

The scope of the claims  [1] A glass production method comprising a step of degassing molten glass under reduced pressure by setting the water vapor concentration of the atmospheric gas in the vacuum degassing tank to 60 mol% or less. [2] The glass manufacturing method according to claim 1, wherein a water vapor concentration of the atmosphere gas is set to 60 mol% or less by introducing a low moisture gas into the atmosphere gas of the vacuum degassing tank. [3] The glass manufacturing method according to claim 1 or 2, wherein the atmospheric gas has a water vapor concentration of 30 mol% or less.  4. The glass production method according to claim 2, wherein the oxygen concentration (volume%) of the low moisture gas is lower than the oxygen concentration (volume%) in the air. 5. The glass production method according to claim 4, wherein the oxygen concentration (volume%) of the low moisture gas is 15 volume% or less.  [6] The water vapor concentration of the atmospheric gas in the vacuum degassing tank for vacuum degassing of the molten glass is measured, and the low moisture gas is supplied to the atmospheric gas in the vacuum degassing tank based on the measurement result of the water vapor concentration. A glass manufacturing method in which the water vapor concentration of the atmospheric gas in the vacuum degassing tank is adjusted to 60 mol% or less by introducing.  [7] A decompression housing to be sucked under reduced pressure, a decompression deaeration tank provided in the decompression housing for performing decompression defoaming of the molten glass, and provided in communication with the decompression defoaming tank, Melting having introducing means for introducing the molten glass into the vacuum degassing tank, and deriving means provided in communication with the vacuum degassing tank and for deriving the molten glass after the vacuum degassing from the vacuum degassing tank A vacuum degassing device for glass,  Water vapor concentration measuring means for measuring the water vapor concentration of the atmospheric gas in the vacuum degassing tank; and low moisture gas introducing means for introducing low moisture gas into the upper space inside the vacuum degassing tank;  A vacuum degassing apparatus for molten glass further comprising:  [8] A water vapor concentration control means that can control the water vapor concentration of the atmospheric gas to a desired value in the vacuum degassing apparatus, and a gas amount that controls the amount of low moisture gas introduced by a signal from the control means The vacuum degassing apparatus according to claim 7, further comprising a control means. [9] The low moisture gas introducing means is provided on the upstream side of the vacuum degassing tank or A vacuum degassing apparatus for molten glass as described in 1.