JP5434077B2 - Glass manufacturing method - Google Patents

Description

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

Conventionally, in order to improve the quality of the molded glass product, a clarification process for removing bubbles generated in the molten glass is used before the molten glass in which the raw material is melted in the melting furnace is molded by the molding apparatus. Yes.
In this clarification step, molten glass is introduced into the reduced-pressure atmosphere, and bubbles in the molten glass flow that flows continuously under this reduced-pressure atmosphere are greatly grown to allow the bubbles contained in the molten glass to rise and break. A vacuum degassing method is known which removes and then discharges from a vacuum atmosphere.

And in such a vacuum degassing method, in order to achieve a suitable vacuum degassing condition, a method that defines the pressure and temperature in the vacuum degassing tank has been proposed (see Patent Document 1 and Patent Document 2). ).
JP 2000-302456 A International Publication No. 02/098810 Pamphlet

However, for example, even if vacuum degassing is performed under suitable vacuum degassing conditions as described above, during the vacuum degassing treatment, the foam layer present on the surface of the molten glass is usually 10 mm or less to 10 mm to several hundred mm. There was a case where so-called bumping occurred. Bumping is a phenomenon in which bubbles that reach the glass surface that normally disappear over 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). . 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 foam layer being enlarged, bubbles may remain in the glass product and cause defects.
In addition, 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 plate deteriorated.

An object of the present invention is to provide a glass manufacturing method in which vacuum degassing is performed with little bumping.
It is another object of the present invention to provide a glass production method for performing degassing under reduced pressure, in which almost no bubbles remain in a glass product derived from the enlargement of the foam layer.
Moreover, it is providing the glass manufacturing method which suppresses volatilization of the specific components (boron etc.) in a molten glass, and performs vacuum degassing.
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 To provide an apparatus.

  The present inventor has studied in detail a phenomenon in which the bubble layer on the surface of the molten glass in the vacuum defoaming tank is enlarged, that is, a vacuum defoaming treatment condition 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 foam layer enlarged and many bubbles remain | survived in glassware. Moreover, when the said water vapor | steam density | concentration exceeded another specific value still higher than this specific value, it discovered that a bubble layer further enlarged and bubbling continued and more bubbles remained in glassware. And the glass manufacturing method which carries out vacuum degassing on the decompression defoaming conditions below these specific values, the vacuum degassing apparatus of the molten glass which can carry out vacuum degassing on such conditions, and the vacuum degassing of such an apparatus It has been found that a method of adjusting the water vapor concentration of the atmospheric gas in the tank solves the above-mentioned problems, and the present invention has been completed.

The present invention provides the following (1) to ( 9 ).
(1) A glass production method comprising a step of degassing molten glass while adjusting a water vapor concentration of atmospheric gas in a vacuum degassing tank to 60 mol% or less.
(2) The glass manufacturing method according to (1) above, wherein a low moisture gas is introduced into the atmospheric gas in the vacuum degassing tank so that the water vapor concentration of the atmospheric gas is 60 mol% or less.
(3) The glass production method according to (1) or (2), wherein the water vapor concentration of the atmospheric gas is adjusted to 30 mol% or less.
(4) The glass production method according to (2) or (3), 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) The water vapor concentration of the atmospheric gas in the vacuum degassing tank for degassing the molten glass under vacuum is measured, and based on the measurement result of the water vapor concentration, a low moisture gas is added to the atmospheric gas in the vacuum degassing tank. The glass manufacturing method which adjusts the water vapor | steam density | concentration of the said atmospheric gas of the said pressure reduction degassing tank to 60 mol% or less by introduce | transducing.
(7) A decompression housing that is sucked under reduced pressure, a decompression deaeration tank that is provided in the decompression housing and performs decompression defoaming of the molten glass, and is 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 And a low moisture gas introduction device that introduces a low moisture gas into an upper space inside the vacuum degassing tank. And a vacuum degassing apparatus for molten glass.
(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 (7), further comprising a control unit.
(9) The vacuum degassing apparatus for molten glass according to (7) or (8), wherein the low moisture gas introduction means is provided on the upstream side of the vacuum degassing tank.

The glass production method of the present invention includes 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, whereby the vacuum degassing of the molten glass without causing bumping. There is an effect that can be performed. And there exists an effect that the defect which generate | occur | produces by the bubble resulting from bumping remaining in a glass product is not produced. Moreover, since the glass manufacturing method of this invention can prevent bumping, glass manufacture can be continued stably.
This “stable manufacturing” is a very important factor in quality control for glass manufacturing apparatuses that are operated day and night. This is because once the quality deteriorates, it is necessary to stop the equipment for repair or adjustment. Moreover, since it is possible to suppress deposits from adhering to the wall or ceiling of the vacuum degassing tank, bumped molten glass can be suppressed from forming defects in the glass product due to the falling, and quality can be improved.
Moreover, since the glass manufacturing method of such this invention reduces the water | moisture content in the atmosphere which promotes volatilization of a specific component (boron etc.), it suppresses volatilization of the specific component (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. Especially for glass for display such as glass for liquid crystal, the standard of composition is strictly defined from the requirement of the characteristics, but boron is very easy to volatilize, so the content of boron is strictly adjusted. There is a need. Therefore, according to the glass manufacturing method of this invention, it is possible to manufacture efficiently the glass which has a composition and flatness within a specification range.

  Moreover, it is preferable that the said water vapor concentration is 30 mol% or less in the glass manufacturing method of this invention. Thereby, in addition to not causing bumping as described above, the enlargement of the foam layer is suppressed, and the generation of many defects in the glass product is suppressed (specifically, per unit mass of the glass product, 0.5 bubbles / kg or less).

  Moreover, the vacuum degassing apparatus of this invention can provide the vacuum degassing apparatus suitable for performing such a glass manufacturing method of this invention.

FIG. 1 is a diagram showing a configuration example of a vacuum degassing apparatus according to the present invention. FIG. 2 is a view showing a vacuum degassing apparatus of 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

DESCRIPTION OF SYMBOLS 1 Decompression degassing apparatus 3 Atmospheric gas 3 'Exhausted atmospheric gas 5 Upper space 6 Opening 7 Low moisture gas 8 Opening 9 Opening 10 Depressurization defoaming apparatus 11 Decompression housing 12 Depressurization defoaming tank 13 Rising pipe 14 Downcomer pipe 15 Thermal insulation DESCRIPTION OF SYMBOLS 20 Melting tank 22 Upstream pit 24 Downstream pit 28 Pump 30 Water vapor | steam density | concentration measurement means 40 Low moisture gas introduction means 41 Low moisture gas generator 42 Flow control valve 44 Flow meter G Molten glass

The glass manufacturing method of this invention is demonstrated.
The glass production method of the present invention comprises a step of defoaming molten glass under reduced pressure with the water vapor concentration of the atmospheric gas in the reduced pressure defoaming tank being 60 mol% or less (hereinafter also referred to as “the reduced pressure defoaming step of the present invention”). . And it is preferable to comprise a raw material melting process as a pre-process, and it is preferable to comprise a shaping | molding process as a post-process. These raw material melting steps and molding steps are not particularly limited, and may be, for example, conventionally known steps. In addition to these steps, other steps 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.

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 whose inside is in a reduced pressure state. There is no particular limitation as long as it is a step of degassing under reduced pressure by setting the water vapor concentration of the atmospheric gas in the vacuum degassing tank to 60 mol% or less.
For example, the reduced-pressure defoaming apparatus measures the water vapor concentration of the atmospheric gas in the reduced-pressure defoaming tank, and introduces a low moisture gas described later into the upper space based on the measurement result of the water vapor concentration. The method for adjusting the water vapor concentration of the atmospheric gas inside the vacuum degassing tank (hereinafter also referred to as “the water content adjusting method of the present invention”) is applied to adjust the water vapor concentration of the atmospheric gas to 60 mol% or less. Thus, the vacuum degassing step of the present invention can be performed. The low moisture gas may be introduced continuously or intermittently.

  The reduced pressure defoaming step of the present invention to which the moisture adjusting method of the present invention is applied can be performed using, for example, the reduced pressure defoaming device of the present invention.

The vacuum degassing apparatus of the present invention will be described.
The vacuum degassing apparatus of the present invention is a vacuum degassing apparatus for degassing molten glass under reduced pressure, and a vacuum degassing tank for defoaming bubbles in the molten glass by flowing the molten glass inside the reduced pressure state. And 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 and degassing the molten glass under reduced pressure, for example, the vacuum degassing apparatus shown in FIG.

  With reference 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 defoaming tank 12, the water vapor concentration measuring means 30, and the vacuum degassing apparatus of the present invention The low moisture gas introduction means 40 is shown.

  First, the vacuum degassing tank 12 will be described with reference to FIG. FIG. 2 is a diagram (cross-sectional view) illustrating a vacuum degassing apparatus 10 (a water vapor concentration measuring means and a low moisture gas introducing means are not described) including the vacuum degassing tank 12 of the present invention.

  In the vacuum degassing apparatus 10 shown in FIG. 2, the cylindrical vacuum degassing tank 12 is housed and disposed 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.

The upper surface of the vacuum degassing tank 12 has a plurality of openings, and the low moisture gas 7 can be introduced into the upper space 5 inside the vacuum degassing tank 12 from the outside of the vacuum housing 11 through at least one opening 6. it can. Further, the opening 8 formed in the decompression housing 11 is connected to decompression means such as a pump (not shown in FIG. 2, shown as a pump 28 in FIG. 1), and the atmosphere gas 3 filling the upper space 5. The inside of the decompression defoaming tank 12 can be decompressed by exhausting it out of the decompression housing 11 (the exhausted one is indicated as atmospheric gas 3 '). 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 provided on the upstream side of the vacuum degassing tank 12, and the opening 8 is provided on the downstream side thereof. Is preferred. By providing the opening 6 constituting a part of the low moisture gas introducing 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 supplied. , It can flow from the upstream side of the vacuum degassing tank 12 toward the downstream side where the opening 8 is provided, and the upper space 5 inside the vacuum degassing tank 12 can be made into an atmosphere gas with a uniform low water vapor concentration. .
Further, for example, a known pressure gauge and thermometer capable of measuring the pressure (P ₁ ) and temperature (T ₁ ) of the atmospheric gas 3 are installed in the vacuum degassing tank 12 (not shown).

As shown in FIG. 2, the ascending pipe 13 communicates with the vacuum degassing tank 12 and is an introduction 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 opening end of the upstream pit 22 and is immersed in the molten glass G in the upstream pit 22.
The downcomer 14 communicates with the vacuum degassing tank 12 and is a lead-out means for lowering the molten glass G after the vacuum degassing from the vacuum degassing tank 12 and leading it to a processing tank (not shown) in a subsequent process. is there. For this reason, the lower end portion of the downcomer pipe 14 is fitted into the opening end of the downstream pit 24 and is 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 ascending pipe 13 and the descending pipe 14 to insulate these.

  In the vacuum degassing apparatus 10 shown in FIG. 2, the vacuum degassing tank 12, the rising pipe 13, and the downfalling pipe 14 are conduits for the molten glass G, and therefore are manufactured using a material having excellent heat resistance and corrosion resistance to the molten glass. Has been. 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 nonmetallic inorganic material, that is, a dense refractory. Specific examples of dense refractories include, for example, electrocast refractories such as alumina electrocast refractories, zirconia electrocast refractories, alumina-zirconia-silica electrocast refractories, and dense alumina refractories. And dense fired refractories such as dense zirconia-silica refractories and dense alumina-zirconia-silica refractories.

The dimension of each component of such a vacuum degassing apparatus 10 can be appropriately selected as necessary. The dimensions of the vacuum degassing tank 12 can 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. it can. In the case of the vacuum degassing tank 12 shown in FIG. 2, specific examples of the dimensions are as follows.
Horizontal length: 1-20m
Inner diameter: 0.2-3m (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.

The decompression housing 11 is made of metal, for example, stainless steel, and has a shape and dimensions that can accommodate the decompression deaeration tank.
Regardless of whether the riser pipe 13 and the downfall pipe 14 are made of platinum, a platinum alloy, or a dense refractory, they can be appropriately selected according to the vacuum degassing apparatus to be used. For example, the dimensions of the ascending pipe 13 and the descending pipe 14 can be configured as follows.
Inner diameter: 0.05 to 0.8 m, more preferably 0.1 to 0.6 m
Length: 0.2-6m, more preferably 0.4-4m
When the uprising pipe 13 and downfalling pipe 14 are made of platinum or a platinum alloy, the wall thickness is preferably 0.4 to 5 mm, more preferably 0.8 to 4 mm.

  The vacuum degassing tank which the vacuum degassing apparatus of this invention has is the vacuum degassing tank 12 which comprises such a structure, for example.

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, and further to the downstream side, a pump 28 as pressure reducing means is connected. With this pump 28, the atmospheric gas 3 ′ discharged from the vacuum degassing tank 12 can be sent to the water vapor concentration measuring means 30. The atmospheric gas 3 ′ discharged from the pump 28 is diffused into the atmosphere after purification, if necessary.

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. . 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.
The water vapor concentration (C) [mol%] of the atmospheric gas 3 ′ may be measured using a commercially available dew point meter, or instead, the water contained in the atmospheric gas 3 ′ is precipitated and the amount ( W) It can also be estimated by measuring [g]. For example, the gas flow rate of the atmospheric gas 3 ′ discharged from the vacuum degassing layer 12 is F _out [m ³ / h], the gas outflow time is t _out [h], and the atmospheric gas is measured by the water vapor concentration measuring means 30. When the pressure and temperature of 3 ′ are P ₂ [Pa] and T ₂ [K], 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 the formula (1) to 60 mol% or less, it is possible to perform degassing of molten glass without causing bumping, and bubbles are generated due to remaining bubbles in the glass product. This produces the effect of not causing defects to occur.

Each unit is as follows.
C: mol%, W: g, T ₂ : K, P ₂ : Pa, F _out : m ³ / h, t _out : h, R (gas constant): J · K / mol

Next, the low moisture gas introduction means 40 included in the vacuum degassing apparatus of the present invention will be described.
In FIG. 1, the low moisture gas introducing means 40 is connected to the upstream side of the vacuum degassing tank 12 by piping or the like. Then, the low moisture gas 7 can be introduced from the low moisture gas introduction means 40 through this pipe or the like.
For example, as shown in FIG. 1, the low moisture gas introduction means 40 includes a low moisture gas generator 41 and a vacuum degassing tank 12 connected by a pipe or the like, and low moisture generated by the low moisture gas generator 41. The gas 7 can be introduced into the upper space 5 of the vacuum degassing tank 12. A flow rate control valve 42 and a flow meter 44 are provided in this order between the low moisture gas generator 41 and the vacuum degassing tank 12, and the amount of introduction of the low moisture gas 7 can be adjusted with these. .
The arrangement of the flow control valve 42 and the flow meter 44 may be reversed.

  Here, the low moisture gas introduction means 40 may have 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. This is preferable because the low moisture gas 7 can be efficiently introduced into the upper space 5.

Further, if the atmosphere is used as the low moisture gas 7, the low moisture gas generator 41 is not necessary. For example, one end of a pipe or the like connected to the upper space 5 is open to the atmosphere by opening and closing the flow control valve 42, and the atmosphere may be introduced into the upper space 5 where the pressure is reduced through this pipe.
Further, when using, for example, an inert gas other than the atmosphere as the low moisture gas 7, a gas that allows the water vapor concentration measuring means 30 to measure the gas component of the atmospheric gas 3 ′ discharged from the upper space 5. It is preferable to have a component meter.

In the present invention, the low moisture gas means a gas whose moisture (water vapor concentration) is lower than that of the atmospheric gas 3 in the upper space 5. Examples of the low moisture gas include air, dry air, inert gas such as N ₂ and Ar, and the like, and not only one kind but also plural kinds. The water vapor concentration of the low moisture gas is preferably 0 to 20 mol%, more preferably 0 to 5 mol%, and still more preferably 0 to 1 mol%. The water vapor concentration of the low moisture gas can be measured using a commercially available outdoor meter or the like.

The vacuum degassing apparatus of the present invention is, for example, the vacuum degassing apparatus 1 having such a vacuum degassing tank 12, a water vapor concentration measuring means 30, and a low moisture gas introducing 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 water gas is introduced by the low water gas introducing means. By appropriately repeating the adjustment such as introducing the water vapor, the water vapor concentration of the atmospheric gas in the upper space can be adjusted to a desired concentration.
For example, since the water vapor concentration (C) obtained by the above equation (1) and the target water vapor concentration (C ₁ ) have the relationship of the following equation (2), the amount of low moisture gas introduced into the upper space: (F _in ) and introduction time (t _in ), the discharge amount (F _OUT ) and discharge time (t _OUT ) of the atmospheric gas from the upper space, and the water vapor concentration (S) [mol%] of the low moisture gas are adjusted. Thus, the water vapor concentration can be set as a target value.

The meaning and unit of each symbol are as follows.
C ₁ : [mol%], V (volume of the upper space): [m ³ ], V _in : [m ³ ], V _out : [m ³ ]

Here, V _in is an introduced gas volume (F _in × t _in ) obtained from an introduction amount (F _in [m ³ / h]) measured by the flow meter 44 and an introduction time (t _in [h]). m ³ ] is a conversion amount in the temperature and pressure of the upper space. Similarly, V _out is an exhaust gas volume (F _out [m ³ / h]) measured by a flow meter included in the water vapor concentration measuring means 30 and an exhaust gas volume (t _out [h]) obtained from the exhaust time (t _out [h]). F _out × t _out ) [m ³ ] is a conversion amount in the temperature and pressure of the upper space.
Further, in order to keep the pressure in the upper space constant, it is necessary to set V _in = V _out .

For example, in order to reduce the water vapor concentration (C) = 20 mol% in the upper space of the volume (V) = 1 m ³ to the target water vapor concentration (C ₁ ) = 10 mol%, when V _in = V _out , The amount of low moisture gas introduced (V _in ) = 0.53 m ³ .
Therefore, when the temperature of the upper space (T ₁ ) = 1673 K and the pressure (P ₁ ) = 25 kPa, the introduction gas temperature (T ₃ ) = 298 K and the pressure (P ₃ ) = 101 kPa at the position of the flow meter 44 are introduced. gas volume _{(F in} × _{t in)} becomes 0.023 ^{[m 3].}
Actually, the evaporation of moisture from the molten glass and apparatus constituent materials or the change of the water vapor concentration due to the leak gas occurs, and therefore it is necessary to constantly adjust.

During the production of glass products, it is preferable to constantly monitor and control the water vapor concentration. Specifically, the vacuum degassing apparatus preferably has a water vapor concentration control means capable of controlling the water vapor concentration of the atmospheric gas to a desired value, and the introduction of the low moisture gas by the signal from the control means. It is preferable to further have a gas amount control means for controlling the amount.
For example, T ₂ , P ₂ , F _OUT , t _OUT , W ₂ , S, F _IN and t _IN are steadily measured, and these data are collected in a computer that allows the water vapor concentration in the upper space to be determined as desired. It is preferable that the vacuum degassing apparatus of the present invention has a water vapor concentration control means that can be controlled so as to be a value. Moreover, it is preferable that the decompression defoaming device of the present invention has a gas amount control means for enabling the computer to control the opening and closing of the flow 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.

  The glass production method of the present invention is preferably performed using such a vacuum degassing apparatus of the present invention, but other methods may be applied. For example, it is not always necessary to introduce gas into the upper space in the vacuum degassing tank as in the vacuum degassing apparatus of the present invention, and when the atmosphere in the vacuum degassing tank and the vacuum housing are connected, What is necessary is just to reduce the water vapor | steam density | concentration of the gas in a housing.

In the glass manufacturing 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 reduction treatment conditions are: the atmospheric gas pressure (P ₁ ) in the upper space inside the vacuum degassing tank is 38 to 460 mmHg (51 to 613 hPa), and the temperature (T ₁ ) is 1100 ° C. to 1500 ° C., especially The processing conditions which perform a vacuum degassing process as 1250 to 1450 degreeC are said.

In the vacuum degassing step of the present invention provided 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, bubbles in the molten glass can be degassed under reduced pressure conditions without causing so-called bumping.
Further, 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, and more preferably 40 mol% or less. And it is preferable for the water vapor concentration to be 30 mol% or less because the foam layer tends to be further thinned. Further, depending on the glass composition, each bubble may shrink or break, which is preferable because the bubble layer becomes thinner. Furthermore, it is preferable because bubbles having a size that is regarded as a defect in the glass product are difficult to remain. If this water vapor concentration is further lower, the probability of defects occurring in the glass product is further reduced. Therefore, it is more preferably 25 mol% or less, more preferably 20 mol% or less, and more preferably 15 mol% or less. More preferably, it is 10 mol% or less, and further preferably 5 mol% or less.

Further, in addition to the above, the present inventor has found that such bubble contraction is a phenomenon that is particularly prominent in molten glass having a specific composition.
Specifically, when the molten glass is borosilicate glass, when the water vapor concentration is 30 mol% or less, the bubbles tend to contract significantly. 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 borosilicate glass.

The borosilicate glass here has the following composition, for example.
Composition _{ranges: SiO 2: 55~74, Al 2} O 3: 10~20, B 2 O 3: 5~12, Al 2 O 3 / B 2 O 3: 1.5~3, MgO: 0~5 , CaO: 0 to 5, SrO: 0 to 12, BaO: 0 to 12, SrO + BaO: 6 to 12 (unit: mass%).

  Conventionally, preferable pressure and temperature conditions in the vacuum degassing tank have been presented, but there has been no example of examining the water vapor concentration. The present inventor has eagerly investigated the cause of bumping or enlargement of the foam layer even when defoaming under the reduced pressure defoaming conditions presented in the past, and focusing on the water vapor concentration that has not been noticed in the past. By doing so, it was found that such a problem can be solved.

Moreover, this inventor also discovered that there exists an effect that volatilization of the specific components (boron etc.) in a molten glass can be suppressed by making water vapor | steam density | concentration into 60 mol% or less. By suppressing volatilization of components such as boron, it is possible to prevent variation in the composition of boron and the like, and to suppress deterioration in flatness due to composition variation.
In addition, since volatilization of easily volatile components, such as Cl, F, and S, can be suppressed, compositional variations of these components can be prevented and deterioration of flatness due to compositional variations can be suppressed. Can do.
These components such as Cl, F, and S are considered to be greatly influenced by moisture volatilization. For example, it is thought that F is volatilized as HF and S is vaporized as H ₂ SO ₄ . Therefore, it is thought that the fluctuation | variation of the said component volatilized with the volatilization of a water | moisture content can be suppressed by making the water | moisture-content density | concentration in a vacuum degassing tank below a certain fixed amount.
In addition, the characteristics of glass have very fine specifications depending on the application, and the composition of the glass is determined in great detail so as to meet the specifications. For example, there is naturally a standard for the content of boron, but 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, there is a possibility that the standard of the content of boron may be deviated. In the present invention, such a problem is 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 moisture adjustment method of the present invention are not limited to ordinary glass, and are preferably used particularly when producing borosilicate glass. I can say that.

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 still more preferably 5% by volume or less. The low moisture gas is preferably a gas not containing oxygen, such as N ₂ gas, Ar gas, CO ₂ or the like.
When the oxygen concentration of the low moisture gas introduced into the upper space is such a value, platinum or a platinum alloy is used as the material of the vacuum defoaming tank in addition to the thinning of the foam layer as described above. In this case, it is preferable because the oxidation of the platinum can be suppressed, the life of the vacuum degassing tank can be extended, and further, the generation of defects derived from platinum can be suppressed in the glass product.

  As mentioned above, it is preferable that the glass manufacturing method of this invention comprises the vacuum degassing process of this invention, and comprises a raw material melting process and a shaping | molding process as a pre-process and a post process. This raw material melting step may be, for example, a conventionally known one. For example, the raw material is melted 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, raw materials prepared by mixing conventionally known materials such as cinnabar, boric acid, limestone, etc. according to the composition of the final glass product can be used. This raw material may contain the desired fining agent. Moreover, this shaping | molding process may be a conventionally well-known thing, for example, a float shaping | molding process, a roll-out shaping | molding process, a fusion shaping | molding process etc. are mentioned, for 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 material 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 2: 59.4%, Al 2} O 3: 17.6%, B 2 O 3: 7.9%, MgO: 3.2%, CaO: 3.7%, SrO: 7.9%, BaO : 0.1%
In addition, although Examples 1-3 performed the experiment using the platinum crucible containing the molten glass instead of the vacuum degassing tank 12 in FIG. 1, the result of the experiment of this crucible is shown in FIG. It can be regarded as equivalent to the result of the vacuum degassing tank 12.

Subsequently, the atmosphere 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 decompression device. After 30 minutes, the molten glass is rapidly cooled and solidified in the crucible, and the number of bubbles (counting those having a diameter of 100 μm or more) present in the solidified sample is measured to determine the bubble density (pieces / kg). Asked. Here, the mass of the molten glass was 5.0 kg, and the number of bubbles in the glass before decompression was almost the same value in each case of the water vapor concentration.
The results are shown in FIG.

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 value of the number of bubbles taken as Log.
When the water vapor concentration is more than 60 mol%, the interface of the molten glass suddenly increased while observing with a CCD camera, and 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, the same test was performed with the low moisture gas that was air in Example 1 being N ₂ , CO ₂ , and Ar, and the water vapor concentration of the atmosphere in the vacuum decompression vessel being less than 1 mol%. The glass composition is the same as in Example 1.
The results are shown in Table 1.

Thus, when the water vapor concentration was 70 mol%, the thickness of the foam layer was 20 mm or more, and so-called bumping was confirmed. When the water vapor concentration was 3 to 47 mol%, a foam layer having a thickness of about 1 to 2 mm was formed, but bumping was not confirmed. Furthermore, when the atmosphere was N ₂ , CO _2, or Ar (the water vapor concentration was less than 1 mol%), no foam layer was generated. From the above results, the water vapor concentration needs to be 60 mol% or less. Moreover, it is preferable that the thickness of a foam layer is about 15 mm or less.

<Example 3>
In the test similar to Example 2, the shrinkage | contraction speed | rate of the bubble in a foam layer was measured for every various atmosphere. Here, the same borosilicate glass as in Example 1 was used as the molten glass.
The results are shown in FIG. In FIG. 4, the bubble diameter indicates 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 bubbles reach the foam layer is the elapsed time 0 s, and the bubble diameter at that time is 1.0.

From FIG. 4, in the case of the atmosphere having a water vapor concentration of 31 mol%, the air bubble contraction rate is faster in the air having a water vapor concentration of 3 mol% and in the case of N ₂ , CO ₂ or Ar having a water vapor concentration of 1 mol% or less. became.
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, various atmospheric water vapor concentrations (1 mol%, 9 mol%, 13 mol%, 19 mol%, 22 mol%, 35 mol%, 70 mol) are shown in which the bubbles float on the surface of the molten glass by vacuum defoaming and then break and disappear. %) And glass composition (soda lime glass: composition A, composition B, composition C). Here, the thickness of the foam layer when about 50 g of glass was melted was measured using a 50 cc transparent quartz glass beaker as a container so that the state of the foam could be observed. The counted by observing the number of bubbles that rise to the molten glass surface (B _S number) and the number of bubbles and foam-breaking and disappearance reached molten glass surface (B _B number) by the CCD camera, the value of Yabuawaritsu (B _B / B _S %) was calculated. The thickness (mm) and the bubble breaking rate (%) of the foam layer are shown in Table 2 below.

  In all cases, the temperature of the molten glass was heated to 1200 ° C. The absolute pressure in the container was 18.7 kPa for composition A, 10.3 kPa for composition B, and 14.4 kPa for composition C. In addition, 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%.

  From Table 2, it can be confirmed that the higher the water vapor concentration of the atmosphere in the container, the lower the bubble breaking rate and the bubbles remain. Specifically, when the water vapor concentration in the atmosphere exceeds 60 mol%, the foam layer has a thickness of 20 mm or more, but when it is 60 mol% or less, it can be confirmed that the foam layer becomes thin. When the water vapor concentration is more than 60 mol%, the interface of the molten glass suddenly increased while observing with a CCD camera, and so-called bumping phenomenon occurred. Moreover, when the water vapor | steam density | concentration of the atmosphere in a container is less than 15 mol%, it turned out that a bubble breaking rate becomes high and is preferable. That is, when the water vapor concentration in the atmosphere in the container is 60 mol% or less, bumping phenomenon can be prevented and the foam layer can be made thin, and when the water vapor concentration is further lowered, the bubble breaking rate is increased and the bubbles disappear. found.

INDUSTRIAL APPLICABILITY The present invention can be applied to a glass manufacturing method including a vacuum degassing apparatus and a vacuum degassing step 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 cited here as disclosure of the specification of the present invention. Incorporated.

Claims (9)

A glass manufacturing method comprising a step of degassing molten glass while adjusting a water vapor concentration of atmospheric gas in a vacuum degassing tank to 60 mol% or less.   The glass manufacturing method of Claim 1 which makes the water vapor | steam density | concentration of the said atmospheric gas 60 mol% or less by introduce | transducing low moisture gas to the atmospheric gas of the said pressure reduction degassing tank. The glass manufacturing method of Claim 1 or 2 which adjusts the water vapor | steam density | concentration of the said atmospheric gas to 30 mol% or less.   The glass manufacturing method of Claim 2 or 3 whose oxygen concentration (volume%) of the said low moisture gas is lower than the oxygen concentration (volume%) in air.   The glass manufacturing method of Claim 4 whose oxygen concentration (volume%) of the said low moisture gas is 15 volume% or less.   Measure the water vapor concentration of the atmospheric gas in the vacuum degassing tank for vacuum degassing of the molten glass, and introduce low moisture gas into the atmospheric gas in the vacuum degassing tank based on the measurement result of the water vapor concentration The glass manufacturing method which adjusts the water vapor | steam density | concentration of the said atmospheric gas of the said pressure reduction degassing tank to 60 mol% or less. A decompression housing that is sucked under reduced pressure, a decompression deaeration tank that is provided in the decompression housing and performs decompression defoaming of the molten glass, and is provided in communication with the decompression defoaming tank. Vacuum degassing of molten glass, which has introduction means for introducing into the vacuum degassing tank, and a derivation means provided in communication with the vacuum degassing tank and for deriving the molten glass after vacuum degassing from the vacuum degassing tank. A foam device,
Water vapor concentration measuring means for measuring the water vapor concentration of the atmospheric gas in the vacuum degassing tank;
A vacuum degassing apparatus for molten glass further comprising low moisture gas introduction means for introducing a low moisture gas into the upper space inside the vacuum degassing tank.   The vacuum degassing apparatus includes a water vapor concentration control means capable of controlling the water vapor concentration of the atmospheric gas to a desired value, and a gas amount control means for controlling the introduction amount of the low moisture gas by a signal from the control means. Furthermore, the vacuum degassing apparatus of Claim 7 which has.   The vacuum degassing apparatus for molten glass according to claim 7 or 8, wherein the low moisture gas introduction means is provided upstream of the vacuum degassing tank.

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