KR20120115209A - Method for vacuum-degassing molten glass and process for producing glass product - Google Patents

Abstract

To find out the optimum pressure defoaming condition when decompression degassing using a chloride-based clarifier.
As a method for degassing the molten glass under reduced pressure by flowing the molten glass in a vacuum degassing tank in which the inside is maintained at a reduced pressure, the molten glass is an alkali free glass, and the pressure in the vacuum degassing tank at the time of performing vacuum degassing is melted. The bubble growth start pressure (P _bg ) (mmHg) or less of glass, and the reboiling pressure (P _rb ) (mmHg) or more of molten glass are hold | maintained, The pressure reduction defoaming method of the molten glass characterized by the above-mentioned.

Description

Pressure reduction defoaming method of molten glass and manufacturing method of glass product {METHOD FOR VACUUM-DEGASSING MOLTEN GLASS AND PROCESS FOR PRODUCING GLASS PRODUCT}

This invention relates to the vacuum degassing method of a molten glass, and the manufacturing method of the glassware using this vacuum degassing method.

Conventionally, in order to improve the quality of the molded glass product, the clarification process of removing the bubble which generate | occur | produced in the molten glass before shape | molding the molten glass which melt | dissolved the raw material in the melting furnace with the shaping | molding apparatus is used.

In this clarification step, a method of growing, floating and removing bubbles in the molten glass by the clarifier is known by adding a clarifier into the raw material in advance and storing and retaining the molten glass obtained by melting the raw material at a predetermined temperature for a predetermined time. have.

Moreover, the molten glass is introduce | transduced in a pressure reduction atmosphere, and in this pressure reduction atmosphere, the bubble in a continuous-flowing molten glass flow is largely grown, the bubble contained in a molten glass rises, it breaks, and removes, and the pressure reduction which discharges from a pressure reduction atmosphere after that is carried out. Defoaming methods are known.

In order to remove foam | bubble efficiently from a molten glass, it is preferable to carry out combining the above two methods, ie, to perform the pressure reduction defoaming method using the molten glass to which the clarifier was added.

Fining agent for the glass, such as _{As 2 O 3, Sb 2 O} 3, SnO 2 , etc. of oxide fining agents, CaSO _4, BaSO _4, etc. of the sulfate-based refining agent, alkali chloride-based refining of metals, such as NaCl the presence do. Among these, since the sulfate-based clarifier has low solubility of SO ₄ ^{2 -in} the alkali free glass having low basicity, the effect of removing bubbles from the molten glass was insufficient.

In addition, since As ₂ O ₃ and Sb ₂ O ₃ , particularly As ₂ O ₃ , have a large load on the environment, it is required to suppress its use.

In addition, the temperature at which oxygen is released is high at 1500 ° C or higher, and SnO ₂ may be difficult to effectively use as a clarifier.

In addition, the chloride of alkali metal is a clarifier which cannot be used because alkali metal will be contained in an alkali free glass when a quantity sufficient for clarification is added.

The present inventors first examined the possibility of being a clarifier of an alkali free glass, and found that the compound containing chlorine exerts an excellent effect as a clarifier combined with vacuum defoaming. As such chloride clarifiers, BaCl ₂ , SrCl ₂ , CaCl ₂ , MgCl ₂ , AlCl ₃ and NH ₄ Cl are exemplified.

The conditions, such as the pressure and temperature in a pressure reduction defoaming tank at the time of performing pressure reduction defoaming, are disclosed by patent documents 1, 2, etc.

International Publication WO2008 / 029649 International Publication WO2008 / 093580

The present inventors, as a refining agent for an alkali-free glass NH ₄ Cl or SrCl ₂ When using a chloride-based clarifier, it has been found that the proportion of chloride contained in the glass composition affects the preferred reduced pressure defoaming conditions.

This invention is based on the said knowledge, and an object of this invention is to provide the vacuum degassing | defoaming method of the alkali free glass which gives the optimal vacuum degassing | defoaming condition, when degassing under reduced pressure using a chloride type clarifier.

In order to achieve the said objective, this invention is a method of degassing a molten glass under reduced pressure by flowing a molten glass in the pressure reduction degassing tank in which the inside was maintained in the pressure reduction state,

The molten glass is an alkali free glass,

The bubble growth start pressure ( _Pbg ) (mmHg) of the molten glass represented by following formula (1) or formula (2) in the pressure reduction degassing tank at the time of implementation of reduced pressure defoaming, and also in following formula (3) It maintains at the _reboiling pressure _Prb (mmHg) or more of the molten glass shown, The pressure reduction defoaming method of the molten glass is provided.

P _bg = (2.6082 x T ₂ -3538.2) x [β-OH] + (-1.2102 x T ₂ +2612.2) x [Cl]-80.3. ... ... (One)

P _bg = (−0.2462 × T ₂ +1121.7) × [β−OH] + (1.9714 × T ₂ −1730.6) × [Cl] -187.3. ... ... (2)

P _rb = 0.8325 x P _bg -59.5. ... ... (3)

(In formula, T <_2> shows the temperature (degreeC) which the viscosity of a molten glass turns into 10 <^2> dPa * s, [beta-OH] shows the (beta) -OH value (mm <^-1> ) of an alkali free glass, and [Cl ] Shows content (mass%) of the chlorine in an alkali free glass When [Cl] is 0.12 mass% or more, P _bg is represented by Formula (1), and when [Cl] is less than 0.12 mass%, P _bg is a formula. Represented by (2))

In addition, the [β-OH] is, 0.15 ~ 0.6 ㎜ ^- In the [Cl] preferably ^1, and is preferably 0.03 - 0.3 mass%.

Moreover, it is preferable that said T <_2> is 1500-1750 degreeC.

Moreover, this invention is equipped with the glass melting process which melts a glass raw material, and manufactures a molten glass, the pressure reduction defoaming process by the pressure reduction defoaming method of said molten glass, and the glass product shaping | molding process which shape | molds the pressure reduction defoaming molten glass. And the manufacturing method of the glass article which has these processes in this order is provided.

In addition, the alkali free glass in this invention is a thing which does not contain an alkali metal, ie, substantially does not contain an alkali metal, except inevitably mixing as an impurity.

According to the vacuum degassing method of this invention, pressure reduction defoaming can be performed on optimal conditions, when carrying out the pressure reduction defoaming of an alkali free glass using a chloride type clarifier. As a result, foam | bubble and a foreign material in the molten glass after pressure reduction degassing | defoaming process are reduced, and the high quality high quality glass with few defects can be manufactured.

Since the pressure reduction defoaming method of this invention uses a chloride type clarifier, it does not adversely affect a human body and the global environment. In addition, the glass article manufactured using the vacuum degassing | defoaming method of this invention does not need the special attention about suppression of a bubble in the handling in a manufacturing plant or a processing plant, and it does not interfere with recycling of glass articles.

BRIEF DESCRIPTION OF THE DRAWINGS It is sectional drawing which shows one structural example of the pressure reduction defoaming apparatus used for the pressure reduction defoaming method of this invention.
2 is a graph plotting the relationship between T ₂ and the coefficient a in the formula (4).
3 is a graph plotting the relationship between T ₂ and the coefficient b in formula (4).
4 is a graph plotting the relationship between T ₂ and the coefficient c of the formula (5).
5 is a graph plotting the relationship between T ₂ and the coefficient d of the formula (5).
6 shows the reboiling pressure P _rb and the bubble growth starting pressure P _bg . It is a graph plotting the relationship of.
7 shows the experimental value (mmHg) of the bubble growth start pressure (P _bg ) and the bubble growth start pressure (when content (mass%) of chlorine is 0.12 mass% or more with respect to alkali-free glass compositions A, B, and C). P _bg ) is a graph plotting the relationship between the calculated value (mmHg).
FIG. 8 shows the experimental value (mmHg) and the bubble growth start pressure of the bubble growth start pressure (P _bg ) when the content (mass%) of chlorine is less than 0.12 mass% with respect to the alkali free glass compositions A, B, and C. P _bg ) is a graph plotting the relationship between the calculated value (mmHg).

EMBODIMENT OF THE INVENTION Hereinafter, the pressure reduction defoaming method of this invention is demonstrated using drawing. BRIEF DESCRIPTION OF THE DRAWINGS It is sectional drawing which shows one structural example of the pressure reduction defoaming apparatus used for the pressure reduction defoaming method of this invention. In the vacuum degassing apparatus 1 shown in FIG. 1, the cylindrical pressure reduction degassing tank 12 is arrange | positioned in the pressure reduction housing 11 so that the long axis may orientate in a horizontal direction. The rising pipe 13 which is oriented in a vertical direction is attached to the lower surface of one end of the pressure reduction degassing tank 12, and the descending pipe 14 is attached to the lower surface of the other end. A part of the rising pipe 13 and the falling pipe 14 is located in the pressure reduction housing 11.

The rising pipe 13 communicates with the vacuum degassing tank 12, and introduces molten glass G from the melting tank 20 into the vacuum degassing tank 12. The downcomer 14 communicates with the vacuum degassing tank 12, and leads the molten glass G after vacuum degassing to the next treatment tank (not shown). In the pressure reduction housing 11, heat insulation materials 15, such as a brick for heat insulation which heat-insulates these, are arrange | positioned around the pressure reduction degassing tank 12, the rising pipe 13, and the downfalling pipe 14. As shown in FIG.

In the vacuum degassing apparatus 1 shown in FIG. 1, since the pressure reduction degassing tank 12, the rising pipe 13, and the downfalling pipe 14 are conduits of a molten glass, the material excellent in heat resistance and corrosion resistance with respect to a molten glass is used. It is manufactured using. For example, it is a strengthening platinum agent formed by dispersing a metal oxide in a platinum agent, a platinum alloy agent, or a platinum or platinum alloy. Further, a ceramic base metal inorganic material, that is, a dense refractory agent may be used. In addition, a platinum or platinum alloy may be incorporated in the dense refractory material.

In the pressure reduction defoaming method of this invention, the pressure reduction defoaming is performed by passing the molten glass G supplied from the dissolution tank 20 through the pressure reduction degassing tank 12 reduced by the predetermined pressure reduction degree. It is preferable that molten glass G is continuously supplied and discharged to the pressure reduction degassing tank 12. Moreover, it is preferable from a productive point of view that the flow rate of the molten glass is 1 to 200 ton / day.

In order to prevent the temperature difference from the molten glass G supplied from the dissolution tank 20, the pressure reduction degassing tank 12 is heated so that the inside may become a temperature range of 1200 degreeC-1600 degreeC, especially 1350 degreeC-1550 degreeC, It is desirable to have.

The molten glass G used by the pressure reduction defoaming method of this invention is an alkali free glass, and the following chloride type clarifier is added to the glass raw material which manufactures an alkali free glass. Specific examples of the chloride-based clarifying _{agent, BaCl 2, SrCl 2, CaCl} 2, MgCl may be mentioned at least one member selected from the group consisting of _2, AlCl ₃ and NH ₄ Cl. Among them, alkaline earth chlorides such as BaCl ₂ , SrCl ₂ , CaCl ₂ , MgCl ₂ , and AlCl ₃ and NH ₄ Cl are usually present as hydrous salts. Thus, the chloride-based clarifying agent is added in the production of alkali-free glass of the present invention, in view of these, there is no worry of _{deliquescent, BaCl 2 · 2H 2 O,} SrCl 2 · preferable 6H ₂ O, and NH ₄ Cl Do.

The content of chlorine in the alkali free glass (hereinafter, may be represented by [Cl] in the present specification) is preferably 0.03 to 0.3 mass%. As for [Cl], it is more preferable that it is 0.05-0.25 mass%. When [Cl] is less than 0.03 mass%, the clarification effect of the alkali free glass may become insufficient.

Moreover, although the use of the chloride of an alkali metal is also considered as a chloride type clarifier, when a sufficient amount is added to the clarification of a molten glass, alkali metal will be contained in an alkali free glass, and the clarifier which consists of chlorides of an alkali metal is not suitable. .

When performing pressure reduction defoaming, the air in the pressure reduction housing 11 is exhausted from the outside by the vacuum pressure reduction means (not shown), such as a vacuum pump, through the suction opening 16 formed in the predetermined point of the pressure reduction housing 11. do. Thereby, the air in the pressure reduction degassing tank 12 accommodated in the pressure reduction housing 11 is exhausted indirectly, and the inside of the pressure reduction degassing tank 12 is pressure-reduced to predetermined pressure. In the pressure reduction defoaming method of this invention, the pressure in the pressure reduction defoaming tank 12 is maintained below bubble growth start pressure _Pbg (mmHg) represented by following formula (1) or (2).

P _bg = (2.6082 x T ₂ -3538.2) x [β-OH] + (-1.2102 x T ₂ +2612.2) x [Cl]-80.3. ... ... (One)

P _bg = (−0.2462 × T ₂ +1121.7) × [β−OH] + (1.9714 × T ₂ −1730.6) × [Cl] -187.3. ... ... (2)

Here, [Cl] in Formula (1) and (2) represents content (mass%) of chlorine in an alkali free glass. When [Cl] is 0.12 mass% or more, bubble growth start pressure _Pbg is represented by said formula (1). On the other hand, when [Cl] is less than 0.12 mass%, P _bg is represented by Formula (2).

In Formulas (1) and (2), T ₂ represents a temperature (° C.) at which the viscosity of the molten glass becomes 10 ² dPa · s, and can be measured using a high temperature rotational viscometer.

Viscosity 10 ² dPa · s is a reference viscosity indicating that the viscosity of the molten glass is sufficiently low. Accordingly, the temperature T _2, the viscosity of the molten glass that is 10 ² dPa · s is a reference temperature of the molten glass, in the case of non-alkali glass for TFT liquid crystal display substrate, 1500 ~ 1750 ℃.

When T <_2> is 1500-1720 degreeC, the floating speed of the bubble in a molten glass becomes quick and it is preferable at the point which is excellent in the defoaming performance at the time of pressure reduction defoaming. T ₂ is more preferably 1560 ~ 1700 ℃, and is 1590 ~ 1680 ℃ is more preferred.

[(Beta) -OH] shows the (beta) -OH value (mm <^-1> ) of an alkali free glass in Formula (1), (2). (beta) -OH value is used as an index of the moisture content in glass. (beta) -OH value can measure the transmittance | permeability of the alkali free glass test piece which shape | molded the molten glass after pressure reduction defoaming to plate shape using a Fourier transform infrared spectrophotometer (FT-IR), and can obtain | require it using the following formula.

Β-OH value = (1 / X) log ₁₀ (T ₁ / T ₂ )

     X: glass thickness (mm)

· T _1: transmittance at the reference wave number 4000 ㎝ ^-1 (%)

T ₂ : Minimum transmittance (%) in the vicinity of the hydroxyl absorption wave number 3570 cm ^-1 .

Β-OH value of an alkali-free glass, 0.15 ~ 0.6 ㎜ ^- preferably ^1. The β-OH value of the alkali free glass is governed by the amount of water in the raw material, the concentration of water vapor in the dissolution tank, the combustion method (oxygen combustion, air combustion) and the like. The adjustment method of (beta) -OH by the water vapor concentration in a dissolution tank is mentioned later. It is preferable that especially (beta) -OH value is 0.2-0.55 mm <^-1> . As the β-OH value, the β-OH value after vitrification is generally used.

In this specification, bubble growth start pressure P _bg is defined as follows.

When the pressure reduction degassing tank 12 is decompressed under the temperature constant conditions, the volume (bubble diameter) of the bubbles existing in the molten glass in the pressure reduction degassing tank 12 increases according to Boyle's law. However, when the pressure reduction degassing tank 12 is decompressed to a certain pressure, the volume (bubble diameter) of the bubbles in the molten glass increases rapidly beyond the law of Boyle. This pressure is called bubble growth start pressure (P _bg ). When the pressure in the pressure reduction degassing tank 12 is kept below bubble growth start pressure _Pbg (mmHg), the bubble contained in a molten glass in the pressure reduction degassing tank 12 can fully be grown. As a result, the bubble in a molten glass can be removed efficiently.

In the present invention, bubble growth start pressure (P _bg ) Can be obtained in the following order.

In order to reproduce the situation in the pressure reduction degassing tank 12, the crucible made from quartz glass containing the cullet of an alkali free glass is arrange | positioned in a vacuum pressure reduction container. The crucible is heated to a predetermined temperature (eg 1300 ° C or 1400 ° C) to melt the alkali free glass. After the alkali free glass melt | dissolves completely, the diameter of the bubble in a molten glass is observed, depressurizing the inside of a vacuum pressure reduction container. In order to observe the diameter of the bubble in a molten glass, what is necessary is just to image | photograph with a CCD camera from the look-in window which formed the bubble in a molten glass in the vacuum pressure reduction container, for example. Moreover, the number of samples of the bubble which measures the bubble diameter is 20 or more.

When the pressure in the vacuum decompression vessel is lowered, the diameter of bubbles in the molten glass increases according to Boyle's law. However, when the inside of a vacuum pressure reduction container is decompressed to a certain pressure, the diameter of the bubble in a molten glass will increase rapidly from Boyle's law. The decompression degree in the vacuum decompression vessel at this time is made into bubble growth start pressure _Pbg .

The inventors of the present invention, bubble growth start pressure (P _bg ) As a result of earnestly examining the relationship between the various parameters related to the vacuum degassing of an alkali free glass, the molten glass has the temperature (T ₂ ) which becomes 10 ² dPa * s, and the (beta) -OH value of an alkali free glass ([ β-OH]) and content ([Cl]) of chlorine in an alkali free glass is bubble growth start pressure (P _bg ) I found out that it affects. Based on this knowledge, bubble growth start pressure (P _bg ) Experimental derivation of the relationship between, and T ₂ , [β-OH], and [Cl] is the above formulas (1) and (2). The derivation procedure of formulas (1) and (2) will be described in more detail.

T ₂ is different from the alkali-free glass with respect to the A ~ C, the content of chlorine in the β-OH value of [β-OH], or alkali-free glass of the alkali-free glass [Cl] are different, and preparing the same alkali-free glass composition different values And bubble growth start pressure _{Pbg was} calculated | required in the said order. Here, NH ₄ Cl was used as the chloride clarifier. Although it will mention later in detail, when melt | dissolving an alkali free glass in the dissolution tank 20, the (beta) -OH value of an alkali free glass can be adjusted by adjusting the ratio of oxygen and air mixed with fuel. The composition of the alkali-free glass A ~ C, and, T ₂ are represented as follows. The composition of the following alkali free glass is the mass% display of the following oxide conversion.

(Alkali Glass A)

SiO ₂ : 59.5 mass%,

Al ₂ O ₃ : 17.7 mass%,

B ₂ O ₃ : 7.9 mass%,

   MgO: 3.2 mass%,

   CaO: 3.7 mass%,

   SrO: 7.9 mass%,

   BaO: 0.1 mass%.

(T ₂ : 1660 ℃)

(Alkali-free glass B)

SiO ₂ : 59.4 mass%,

Al ₂ O ₃ : 16.9 mass%,

B ₂ O ₃ : 8.6 mass%,

   MgO: 4.0 mass%,

   CaO: 5.4 mass%,

   SrO: 5.7 mass%,

   BaO: 0.0 mass%.

(T ₂ : 1617 ℃)

(Alkali-free glass C)

SiO ₂ : 59.5 mass%,

Al ₂ O ₃ : 17.0 mass%,

B ₂ O ₃ : 8.0 mass%,

   MgO: 4.7 mass%,

   CaO: 6.0 mass%,

   SrO: 4.8 mass%,

   BaO: 0.0 mass%.

(T ₂ : 1597 ℃)

In any of alkali free glasses A-C, when content [Cl] of chlorine in an alkali free glass is 0.12 mass% or more, bubble growth start pressure (P _bg ) and (beta) -OH value of an alkali free glass ([β- OH]) and the relationship shown by following formula (4) about content ([Cl]) of the chlorine in an alkali free glass were found.

P _bg = a × [β-OH] + b × [Cl] -80.3... ... ... (4)

Formula (4) about each alkali free glass A-C is as follows.

(Alkali Glass A)

P _bg = 800.6 x [β-OH] + 660.1 x [Cl]-80.3. ... ... (4-A)

(Alkali-free glass B)

P _bg = 650.0 × [β-OH] + 664.9 × [Cl] -80.3... ... ... (4-B)

(Alkali-free glass C)

P _bg = 646.9 x [β-OH] + 672.8 x [Cl]-80.3. ... ... (4-C)

2 is T ₂ based on the results obtained above. And a graph plotting the relationship between the coefficient a in the formula (4). 3 shows T ₂ based on the results obtained above. And a graph plotting the relationship between the coefficient b in formula (4).

What was calculated | required from the regression line shown to FIG. 2, 3 is said Formula (1).

On the other hand, when content of chlorine in an alkali free glass was less than 0.12 mass%, it discovered that the relationship shown by following formula (5) holds with respect to P _bg , [(beta) -OH], and [Cl].

P _bg = c x [β-OH] + d x [Cl]-187.3. ... ... (5)

Formula (5) about each alkali free glass A-C is as follows.

(Alkali Glass A)

P _bg = 713.6 x [β-OH] + 1530.0 x [Cl]-187.3. ... ... (5-A)

(Alkali-free glass B)

P _bg = 721.7 x [β-OH] + 1494.6 x [Cl]-187.3. ... ... (5-B)

(Alkali-free glass C)

P _bg = 729.8 x [β-OH] + 1392.1 x [Cl]-187.3. ... ... (5-C)

4 is T ₂ based on the results obtained above. And a graph plotting the relationship between the coefficient c in the equation (5). 5 is based on the results obtained above, T ₂ And a graph plotting the relationship between the coefficient d in equation (5).

It is said formula (2) calculated | required from the regression line shown to FIG. 4,5.

As described above, in the vacuum degassing method of the present invention, the pressure in the vacuum degassing tank 12 is kept below the bubble growth start pressure P _bg (mmHg) represented by the formula (1), but the vacuum degassing tank 12 When the internal pressure is extremely low, there exists a possibility that reboiling may generate | occur | produce in the molten glass which flows through the pressure reduction degassing tank 12.

For this reason, in the pressure reduction defoaming method of this invention, the pressure in the pressure reduction defoaming tank 12 is maintained above the _reboiling pressure _Prb (mmHg) of the molten glass represented by following formula (3).

P _rb = 0.8325 x P _bg -59.5... ... ... (3)

In the present specification, the reboiling pressure P _rb Is defined as

In order to fully grow the bubble contained in a molten glass, it is preferable to make the pressure in the pressure reduction degassing tank 12 as low as possible. However, when the pressure in the pressure reduction degassing tank 12 is made extremely low, a bubble may generate | occur | produce in the glass interface which contact | connects the pressure reduction defoaming tank 12 of a platinum agent, a platinum alloy agent, or a dense refractory agent. This phenomenon is called reboil, and the pressure in the vacuum degassing tank 12 at this time is called reboiling pressure P _rb .

In addition, the reboiling pressure P _rb can be obtained in the following order.

In order to reproduce the situation in the vacuum degassing tank 12, the quartz glass crucible containing the cullet of the alkali free glass is arrange | positioned in a vacuum pressure reduction container. The crucible is heated to a predetermined temperature (eg 1300 ° C. or 1400 ° C.) to melt the alkali free glass. The test piece produced using the material which comprises the pressure reduction degassing tank, more exactly, the material which comprises the glass contact surface of a pressure reduction degassing tank (platinum or a platinum alloy, or dense refractory body) is immersed in molten glass. In this state, the inside of a vacuum decompression vessel is gradually reduced, and generation | occurrence | production of the bubble in the glass interface of a test piece is observed. _Reboiling pressure (P _rb ) of the vacuum decompression vessel when bubbles are generated at the glass interface .

The inventors of the present invention, _reboiling pressure (P _rb ) As a result of earnestly examining the relationship between the various parameters related to the reduced pressure defoaming of an alkali free glass, reboiling pressure (P _rb ) and bubble growth start pressure (P _bg ) I found out that a specific relationship exists.

The formula (3) is a reboiling pressure (P _rb ) And bubble growth onset pressure (P _bg ) This can be specified by plotting the relationship of. 6 shows the reboiling pressure P _rb and the bubble growth start pressure P _bg . It is a graph plotting the relationship of.

In FIG. 6, the platinum-rhodium alloy (90 mass% of platinum, 10 mass% rhodium) was used for the test piece immersed in a molten glass. In addition, alkali free glass A-C was used as a molten glass. The temperature of the molten glass was 1400 degreeC.

In the pressure reduction defoaming method of this invention, the pressure in the pressure reduction defoaming tank 12 is maintained above _reboiling pressure _Prb (mmHg). When the pressure in the vacuum degassing tank 12 is maintained above the _reboiling pressure P _rb (mmHg), reboiling is prevented from occurring in the molten glass flowing through the vacuum degassing tank 12. As a result, the number of bubbles which remain in the molten glass after pressure reduction degassing | defoaming process is reduced, and the high quality glass of high functionality with few bubbles can be manufactured.

That is, in the vacuum degassing | defoaming method of this invention, the bubble growth start pressure (P _bg ) (mmHg) shown by the pressure in the vacuum degassing tank 12 as said Formula (1), (2) or less, and is further represented by said Formula (3) By maintaining above the reboiling pressure P _rb (mmHg), the bubbles contained in the molten glass can be sufficiently grown in the vacuum degassing tank 12, and the bubbles in the molten glass can be efficiently removed, Reboiling is prevented from occurring in the molten glass flowing through the degassing tank 12. As a result, the bubble remaining in the molten glass after pressure reduction degassing | defoaming process is reduced very much, and the highly functional high quality glass with very few bubbles can be manufactured.

As a 1st example of the alkali free glass applied in the vacuum degassing method of this invention, the composition of the alkali free glass containing the following components by the mass% display of the following oxide conversion is mentioned preferably.

SiO ₂ : 50-66 mass%,

Al ₂ O ₃ : 10.5-24 mass%,

B ₂ O ₃ : 0-12 mass%,

   MgO: 0-8 mass%,

   CaO: 0-14.5 mass%,

   SrO: 0-24 mass%,

   BaO: 0-13.5 mass%,

   MgO + CaO + SrO + BaO: 9-29.5 mass%.

As a 2nd example of the alkali free glass applied in the pressure reduction defoaming method of this invention, the composition of the alkali free glass containing the following components by the mass% display of the following oxide conversion is mentioned more preferable.

SiO ₂ : 58-66 mass%,

Al ₂ O ₃ : 15-22 mass%,

B ₂ O ₃ : 0-12 mass%,

   MgO: 0-8 mass%,

   CaO: 0-9 mass%,

   SrO: 3-12.5 mass%,

   BaO: 0-2 mass%,

   MgO + CaO + SrO + BaO: 9-18 mass%.

The reason for limitation of the range of each component of said alkali free glass composition is demonstrated below.

SiO ₂ is 66% greater than the solubility of the glass is decreased, and devitrification is apt to. Preferably it is 64% or less, More preferably, it is 62% or less. If it is less than 50%, specific gravity increase, a strain point fall, an thermal expansion coefficient increase, and the chemical-resistance fall will occur. Preferably it is 58% or more and 58.5% or more, More preferably, it is 59% or more.

Al ₂ O ₃ is essential as a component that suppresses the phase separation of the glass and increases the strain point. When it exceeds 24%, it will become easy to devitrify and the chemical-resistant fall will occur. Preferably it is 22% or less and 20% or less, More preferably, it is 18% or less. If it is less than 10.5%, glass will become easy to powder, or a strain point will fall. Preferably it is 15% or more and 15.5% or more, More preferably, it is 16% or more.

B ₂ O ₃ is not essential, to reduce the specific gravity, the components that make it difficult to increase the solubility of the glass, the devitrification. If it exceeds 22%, a strain point will fall, chemical resistance will fall, or volatilization at the time of glass melting will become remarkable, and the heterogeneity of glass will increase. Preferably it is 12% or less, More preferably, it is 9% or less. When it is less than 5%, specific gravity increases, solubility of glass falls, and it becomes easy to devitrify, Therefore, 5% or more is preferable, Preferably it is 6% or more, More preferably, it is 7% or more.

Although MgO is not essential, it is a component which makes specific gravity small and improves the solubility of glass. If it is more than 8%, glass will be easy to powder, it will be easy to devitrify, or chemical-resistance will fall. Preferably it is 6% or less, More preferably, it is 5% or less. When it contains MgO, it is preferable to contain 1% or more. It is preferable to contain 3% or more especially in order to reduce specific gravity, maintaining solubility.

Although CaO is not essential, it can contain up to 14.5% because it increases the solubility of glass and makes it hard to devitrify. If it is more than 14.5%, specific gravity will increase, a thermal expansion coefficient will become large and it will become easy to devitrify rather. Preferably it is 9% or less and 8% or less, More preferably, it is 7% or less. When it contains CaO, it is preferable to contain 2% or more. More preferably, it is 3.5% or more.

SrO is a component which suppresses powder phase of glass and makes it hard to devitrify. If it is more than 24%, specific gravity will increase, a thermal expansion coefficient will become large and it will become easy to devitrify rather. Preferably it is 12.5% or less and 10.5% or less, More preferably, it is 8.5% or less. Considering the addition of chloride as a clarifier, it is preferable to use SrCl ₂ · 6H ₂ O or BaCl ₂ · 2H ₂ O because there is no concern about deliquescent and it is easy to remain in the glass at the time of dissolving the raw materials. In order to give a freedom degree to the addition amount of Cl, as a glass component, it is preferable to contain 3% or more of SrO. If SrO is less than 3%, the amount of Cl added is restricted, which is not preferable. Preferably it is 4% or more, More preferably, it is 4.5% or more.

BaO can contain up to 13.5% because it suppresses powder phase of glass and makes it hard to devitrify. If it is more than 13.5%, specific gravity will increase and a thermal expansion coefficient will become large. Preferably it is 2% or less and 1% or less, More preferably, it is 0.1% or less. In particular, when weight reduction of a glass substrate is important, it is preferable not to contain substantially.

As ₂ O ₃ and Sb ₂ O ₃ is, it is preferred that it does not contain, and except that the unavoidably incorporated as impurities, that is, does not contain substantially. In addition, for in the range not contrary to the object of the present invention, such as improved solubility, ZrO ₂ Other trace components can be contained up to 5 mass% in total amount.

According to the vacuum degassing method of the present invention, for example, as compared with the aforementioned alkali-free glass A ~ C, SiO ₂ and Al ₂ O ₃ Also in the case of poorly soluble alkali-free glass D (shown in mass% in terms of oxides below) containing a large amount of decompression, decompression degassing can be performed under optimum conditions, and the effect of reducing the occurrence of bubbles and foreign matters can be reduced. Obtained.

(Alkali-free glass D)

SiO ₂ : 62 mass%,

Al ₂ O ₃ : 20 wt%,

B ₂ O ₃ : 0% by mass,

   MgO: 4.7 mass%,

   CaO: 4.4 mass%,

   SrO: 8.1 mass%,

ZrO ₂ : 0.9 mass%

(T ₂ : 1690 ℃)

In the vacuum degassing method of this invention, you may use together a clarifier as a clarifier. In this case, the possible combination other fining agents include, specifically, for example, there may be mentioned SO _3, F, SnO ₂ or the like. These other clarifiers can be contained in an alkali free glass at 2 mass% or less, Preferably it is 1 mass% or less, More preferably, it can contain 0.5 mass% or less.

In the vacuum degassing method of this invention, it may be necessary to adjust [(beta) -OH], ie, the moisture content of a molten glass. The moisture content in a molten glass can be adjusted by changing the composition of the gas mixed with the fuel at the time of burning a fuel, ie, the ratio of oxygen and air mixed with a fuel.

The dimension of each component of the vacuum degassing apparatus used for the vacuum degassing method of this invention can be suitably selected as needed. The dimension of a pressure reduction degassing tank can be suitably selected according to the pressure reduction defoaming apparatus to be used, regardless of whether a pressure reduction degassing tank is a platinum agent, a platinum alloy agent, or a dense refractory agent. In the case of the vacuum degassing tank 12 shown in FIG. 1, the specific example of the dimension is as follows.

Length in the horizontal direction: 1 to 20 m

Internal diameter: 0.2 to 3 m (cross section)

When the pressure reduction degassing tank 12 is made of platinum or a platinum alloy, it is preferable that thickness is 0.5-4 mm.

The pressure reduction housing 11 is metal, for example, stainless steel, and has the shape and dimension which can accommodate a pressure reduction degassing tank.

The rising pipe 13 and the falling pipe 14 can be appropriately selected according to the vacuum degassing apparatus to be used regardless of whether they are made of platinum, platinum alloy, or dense refractory. For example, the dimension of the riser 13 and the downtake 14 can be comprised as follows.

Inner diameter: 0.05 to 0.8 m

Length: 0.2-6 m

In the case where the rising pipe 13 and the falling pipe 14 are made of platinum or a platinum alloy, the thickness is preferably 0.4 to 5 mm.

The manufacturing method of the glassware of this invention is a glass melting process which melts a glass raw material and manufactures a molten glass, the vacuum degassing | defoaming process by the pressure reduction defoaming method of said molten glass, and the glassware which shape | molds the pressure reduction defoaming molten glass. Each step of the molding step is provided in this order.

The above-mentioned glass melting process can employ | adopt a conventionally well-known glass melting method, for example, predetermined glass raw material by heating the glass raw material mix | blended and mixed according to the kind of glass to about 1400 degreeC or more. To melt. It will not specifically limit, if it is a raw material suitable for the alkali free glass which also manufactures the glass raw material used, For example, using the raw material used as a silica sand, boric acid, limestone, aluminum oxide, strontium carbonate, magnesium oxide, other well-known glass components, The glass raw material which combined together to become the composition of the product of the target alkali free glass can be used. The chloride-based clarifier employed in the present invention described above is added to the glass raw material in a predetermined amount. Moreover, the shaping | molding method of a conventionally well-known glass article can also be employ | adopted for a glass article shaping | molding process. When manufacturing a glass plate as a glass product, various shaping | molding methods, such as a float plate glass shaping | molding method, a rollout shaping | molding method, and a fusion shaping | molding method, can be used, for example.

Example

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated more concretely based on an Example. However, the present invention is not limited to this.

(Example 1)

In this embodiment, [β-OH] is 0.29 ㎜ ^- uses a non-alkali glass A, which is known in advance to be the ^first. NH ₄ Cl is added as chloride clarifier. In addition, NH ₄ Cl is added in an amount such that the mass% of chlorine becomes 0.20 mass% with respect to the total mass after vitrification.

From said formula (1), bubble growth start pressure _Pbg is 270 mmHg.

_Reboiling pressure _Prb is set to 165 mmHg from P _bg obtained here and said Formula (3).

A platinum alloy of Pt 90% / Rh 10% having a width of 45 mm, a depth of 7 mm, and a thickness of 1 mm was placed in a quartz glass container having a width of 50 mm x 10 mm x 50 mm in height and agglomerate-free alkali thereon. Place 50 g of Glass A. Then, the quartz glass container is put into an electric furnace, it heats to 1400 degreeC, and the alkali free glass A is melted.

Next, the atmospheric pressure of an electric furnace is reduced to a predetermined pressure, and the bubble amount in a molten glass is observed. Moreover, the bubble amount in a molten glass confirms visually from the look-in window formed in the side surface of an electric furnace.

When the atmospheric pressure of an electric furnace is maintained at 165 mmHg or more which is reboiling pressure P _rb and 270 mmHg or less which is bubble growth starting pressure P _bg , it is confirmed that the amount of bubbles remaining in a molten glass is very small. On the other hand, if the atmospheric pressure of the electric furnace is kept below 165 mmHg, which is the reboiling pressure P _rb , since a remarkable increase is observed in the amount of bubbles generated from the platinum plate in the molten glass, the amount of bubbles remaining in the molten glass is very large. It is confirmed.

(Example 2)

In the present Example, it carries out similarly to Example 1 except having added NH ₄ Cl to the alkali free glass A in the amount which will make the mass% of chlorine to 0.07 mass% with respect to the total mass after vitrification.

From the expression (2), the bubble growth starting pressure (P _bg) is the 127 mmHg.

P _bg obtained here From the above formula (3), the reboiling pressure P _rb is 46 mmHg.

When the atmospheric pressure of an electric furnace is maintained at 46 mmHg or more which is reboiling pressure P _rb and 127 mmHg or less which is bubble growth start pressure P _bg , it is confirmed that the amount of bubbles remaining in a molten glass is very small. On the other hand, when the atmospheric pressure of the electric furnace is kept below 46 mmHg, which is the reboiling pressure P _rb , a remarkable increase is observed in the amount of bubbles generated from the platinum plate in the molten glass, so that a large amount of bubbles remaining in the molten glass is very large. It is confirmed.

(Example 3)

In this embodiment, [β-OH] is 0.29 ㎜ ^- uses a non-alkali glass, which is known in advance that the B ^1. NH ₄ Cl is added as chloride clarifier. In addition, NH ₄ Cl is added in an amount such that the mass% of chlorine becomes 0.20 mass% with respect to the total mass after vitrification.

From the equation (1), the bubble growth starting pressure (P _bg) is the 248 mmHg.

From P _bg obtained here and said Formula (3), _reboiling pressure P _rb is set to 147 mmHg.

A platinum alloy of Pt 90% / Rh 10% having a width of 45 mm, a depth of 7 mm, and a thickness of 1 mm was placed in a quartz glass container having a width of 50 mm x 10 mm x 50 mm in height and agglomerate-free alkali thereon. Place 50 g of Glass B. Then, the quartz glass container is put into an electric furnace, it heats to 1400 degreeC, and the alkali free glass B is melted.

Next, the atmospheric pressure of an electric furnace is reduced to a predetermined pressure, and the bubble amount in a molten glass is observed. Moreover, the bubble amount in a molten glass confirms visually from the look-in window formed in the side surface of an electric furnace.

When the atmospheric pressure of the electric furnace is maintained at 147 mmHg or more, which is the reboiling pressure P _rb , and 248 mmHg or less, which is the bubble growth start pressure P _bg , it is confirmed that the amount of bubbles remaining in the molten glass is very small. On the other hand, when the atmospheric pressure of the electric furnace is kept below 147 mmHg, which is the reboiling pressure P _rb , a remarkable increase is observed in the amount of bubbles generated from the platinum plate in the molten glass, so that the amount of bubbles remaining in the molten glass is very large. It is confirmed.

(Example 4)

In the present Example, it carries out similarly to Example 3 except having added NH ₄ Cl to the alkali free glass B in the quantity which the mass% of chlorine with respect to the total mass after vitrification turns into 0.07 mass%.

From said formula (2), bubble growth start pressure _Pbg is 125 mmHg.

P _bg obtained here From the above formula (3), the reboiling pressure P _rb is 45 mmHg.

When the furnace pressure in the atmosphere, see Lee pressure (P _rb) of more than 45 mmHg, addition, the bubble growth starting pressure maintained at not more than 125 mmHg (P _bg), it is confirmed that a very small amount of bubbles remaining in the molten glass. On the other hand, if the atmospheric pressure of the electric furnace is kept below 45 mmHg, which is the reboiling pressure P _rb , since a remarkable increase is observed in the amount of bubbles generated from the platinum plate in the molten glass, the amount of bubbles remaining in the molten glass is very large. It is confirmed.

(Example 5)

In this embodiment, [β-OH] is 0.29 ㎜ ^- uses a non-alkali glass, which is known in advance that the C ^1. NH ₄ Cl is added as chloride clarifier. In addition, NH ₄ Cl is added in an amount such that the mass% of chlorine becomes 0.20 mass% with respect to the total mass after vitrification.

From said formula (1), bubble growth start pressure _Pbg is 237 mmHg.

From P _bg obtained here and said Formula (3), _reboiling pressure P _rb is 138 mmHg.

A platinum alloy of Pt 90% / Rh 10% having a width of 45 mm, a depth of 7 mm, and a thickness of 1 mm was placed in a quartz glass container having a width of 50 mm x 10 mm x 50 mm in height and agglomerate-free alkali thereon. Place 50 g of glass C. Then, the quartz glass container is put into an electric furnace, it heats to 1400 degreeC, and the alkali free glass C is melted.

Next, the atmospheric pressure of an electric furnace is reduced to a predetermined pressure, and the bubble amount in a molten glass is observed. Moreover, the bubble amount in a molten glass confirms visually from the look-in window formed in the side surface of an electric furnace.

When the atmospheric pressure of the electric furnace is maintained at 138 mmHg or more, which is the reboiling pressure P _rb , and 237 mmHg or less, which is the bubble growth start pressure P _bg , it is confirmed that the amount of bubbles remaining in the molten glass is very small. On the other hand, if the atmospheric pressure of the electric furnace is kept below 138 mmHg, which is the reboiling pressure P _rb , since a remarkable increase is observed in the amount of bubbles generated from the platinum plate in the molten glass, there is a very large amount of bubbles remaining in the molten glass. It is confirmed.

(Example 6)

In the present Example, it carries out similarly to Example 5 except having added NH ₄ Cl in the alkali free glass C in the quantity which will make the mass% of chlorine to 0.07 mass% with respect to the total mass after vitrification.

From said formula (2), bubble growth start pressure _Pbg is 123 mmHg.

P _bg obtained here From the above formula (3), the reboiling pressure P _rb is 43 mmHg.

When the atmospheric pressure of an electric furnace is maintained at 43 mmHg or more which is reboiling pressure P _rb and 123 mmHg or less which is bubble growth start pressure P _bg , it is confirmed that the amount of bubbles remaining in a molten glass is very small. On the other hand, if the atmospheric pressure of the electric furnace is kept below 43 mmHg, which is the reboiling pressure P _rb , since a remarkable increase is observed in the amount of bubbles generated from the platinum plate in the molten glass, there is a very large amount of bubbles remaining in the molten glass. It is confirmed.

(Example 7)

In this example, T ₂ It uses a non-alkali glass, which is known in advance that the D ^{1 -} 1690 ℃, [β-OH] is 0.29 ㎜. NH ₄ Cl is added as chloride clarifier. In addition, NH ₄ Cl is added in an amount such that the mass% of chlorine becomes 0.20 mass% with respect to the total mass after vitrification.

From said formula (1), bubble growth start pressure _Pbg is 285 mmHg.

P _bg obtained here From the above formula (3), the reboiling pressure P _rb is 178 mmHg.

A platinum alloy of Pt 90% / Rh 10% having a width of 45 mm, a depth of 7 mm, and a thickness of 1 mm was placed in a quartz glass container having a width of 50 mm x 10 mm x 50 mm in height and agglomerate-free alkali thereon. Place 50 g of glass D. Then, the quartz glass container is put into an electric furnace, and it heats to 1475 degreeC, and the alkali free glass D is melted.

Next, the atmospheric pressure of an electric furnace is reduced to a predetermined pressure, and the bubble amount in a molten glass is observed. Moreover, the bubble amount in a molten glass confirms visually from the look-in window formed in the side surface of an electric furnace.

When the atmospheric pressure of an electric furnace is maintained at 178 mmHg or more which is reboiling pressure P _rb and 285 mmHg or less which is bubble growth start pressure P _bg , it is confirmed that the amount of bubbles remaining in a molten glass is very small. On the other hand, when the atmospheric pressure of the electric furnace is kept below 178 mmHg, which is the reboiling pressure P _rb , a remarkable increase is observed in the amount of bubbles generated from the platinum plate in the molten glass, so that a large amount of bubbles remaining in the molten glass is very large. It is confirmed.

(Example 8)

In the present Example, it carries out similarly to Example 3 except having added NH ₄ Cl to the alkali free glass D in the quantity which will make the mass% of chlorine to 0.07 mass% with respect to the total mass after vitrification.

From said formula (2), bubble growth start pressure _Pbg is 129 mmHg.

P _bg obtained here From the above formula (3), the reboiling pressure P _rb is 48 mmHg.

When the atmospheric pressure of an electric furnace is maintained at 48 mmHg or more which is reboiling pressure P _rb , and below 129 mmHg which is bubble growth start pressure P _bg , it is confirmed that the amount of bubbles remaining in a molten glass is very small. On the other hand, if the atmospheric pressure of the electric furnace is kept below 48 mmHg, which is the reboiling pressure P _rb , since a remarkable increase is observed in the amount of bubbles generated from the platinum plate in the molten glass, there is a very large amount of bubbles remaining in the molten glass. It is confirmed.

(Example 9)

Here, about the alkali free glass A, B, C mentioned above, the experiment result which shows the effectiveness of Formula (1) and Formula (2) is shown to Tables 1-5 and FIGS. In the experiment, the bubble growth start pressure (P _bg ) was obtained by changing the β-OH value (mm ⁻¹ ) and the content (mass%) of chlorine with respect to each glass composition. Each glass puts about 50 g of molten glass in the quartz cell, and melt | dissolves in predetermined temperature in the electric furnace which has a window for observation. After the glass is dissolved, the pressure is reduced to a desired pressure under a constant speed, and then a change in the bubble diameter is photographed by a CCD camera under a constant pressure and recorded. After the experiment was completed, the change in bubble diameter was analyzed to determine the bubble growth start pressure (P _bg ).

Table 1 to Table 5, the glass temperature, β-OH value during cell observation (㎜ ^-1), the content of chlorine (% by weight), the bubble growth starting pressure (P _bg) of experimental values (mmHg), the bubble growth starting pressure The calculated value (mmHg) by Formula (1) or Formula (2) of (P _bg ) was described. In Table 1-Table 3, each result with respect to the example of 122 whose content (mass%) of chlorine is 0.12 mass% or more with respect to the alkali free glass compositions A, B, and C is shown, respectively. In addition, in Tables 4-5, the result of 41 cases whose content (mass%) of chlorine is less than 0.12 mass% in alkali free glass compositions A, B, and C is shown.

7, the alkali-free glass compositions A, B, with respect to C, when the content of chlorine (% by weight) is not less than 0.12 mass%, and experimental values (mmHg) and the bubble growth starting pressure of the bubble growth starting pressure (P _bg) ( 122 shows a correlation of the relationship between the calculated points (mmHg) of P _bg). 8 shows the experimental value (mmHg) of the bubble growth start pressure (P _bg ) and the bubble growth start pressure (when the content (mass%) of chlorine is less than 0.12 mass% with respect to the alkali free glass compositions A, B, and C). 41 shows a correlation of the relationship between the calculated points (mmHg) of P _bg).

The result of FIG. 7 shows that the slope of the regression equation is 0.92 and the square of the correlation coefficient is 0.82, and equation (1) estimates the experimental value well. The result of FIG. 8 shows that the slope of the regression equation is 0.97 and the square of the correlation coefficient is 0.89, and equation (2) estimates the experimental value well. From these, it turns out that Formula (1) and Formula (2) are effective at estimating bubble growth start pressure _Pbg . The same results are obtained even if the data of the example for the alkali free glass D are plotted on the graphs of FIGS. 7 and 8. Moreover, although the glass temperature at the time of observing a bubble was shown in Tables 1-5, Formula (1) and Formula (2) of this invention are not prescribed | regulated about the glass temperature at the time of a bubble generation. This is considered to be because the clarification according to the present invention is mainly clarification involving water, and the water has a small temperature dependency of solubility.

Industrial availability

According to the vacuum degassing | defoaming method of the molten glass of this invention, it melts in a pressure reduction degassing tank by maintaining the pressure of a pressure reduction degassing tank below bubble growth start pressure (P _bg ) and more than reboiling pressure (P _rb ) (mmHg). Bubbles contained in the glass can be sufficiently grown, and bubbles in the molten glass can be efficiently removed, while reboiling is prevented from occurring in the molten glass flowing through the vacuum degassing tank. As a result, melting after the vacuum degassing treatment is performed. The bubbles remaining in the glass are extremely reduced, and a highly functional high quality glass having very few bubbles can be produced. In this manner, a molten glass and a glass product having excellent bubble quality can be obtained, and in particular, an alkali free glass substrate for FPD can be produced, which is useful.

In addition, all the content of the JP Patent application 2009-294230, a claim, drawing, and the abstract for which it applied on December 25, 2009 is referred here, and it takes in as an indication of this invention.

1: vacuum degassing apparatus
11: pressure reducing housing
12: vacuum degassing tank
13: riser
14 down pipe
15: heat insulation
16: suction opening
20: dissolution tank

Claims (7)

As a method of degassing a molten glass under reduced pressure by flowing a molten glass in the pressure reduction degassing tank in which the inside was maintained in the pressure reduction state,
The molten glass is an alkali free glass,
The bubble growth start pressure ( _Pbg ) (mmHg) of the molten glass represented by following formula (1) or formula (2) in the pressure reduction degassing tank at the time of implementation of reduced pressure defoaming, and also in following formula (3) The pressure reduction defoaming method of the molten glass hold | maintains more than the _reboiling pressure _Prb (mmHg) of the molten glass shown.
P _bg = (2.6082 x T ₂ -3538.2) x [β-OH] + (-1.2102 x T ₂ +2612.2) x [Cl]-80.3. ... ... (One)
P _bg = (−0.2462 × T ₂ +1121.7) × [β−OH] + (1.9714 × T ₂ −1730.6) × [Cl] -187.3. ... ... (2)
P _rb = 0.8325 x P _bg -59.5... ... ... (3)
(In formula, T <_2> shows the temperature (degreeC) which the viscosity of a molten glass turns into 10 <^2> dPa * s, [beta-OH] shows the (beta) -OH value (mm <^-1> ) of an alkali free glass, and [Cl ] Shows content (mass%) of the chlorine in an alkali free glass When [Cl] is 0.12 mass% or more, P _bg is represented by Formula (1), and when [Cl] is less than 0.12 mass%, P _bg is a formula. Represented by (2)) The method of claim 1,
The pressure reduction defoaming method of the molten glass whose said [(beta) -OH] is 0.15-0.6 mm ^{- 1} . The method according to claim 1 or 2,
The pressure reduction defoaming method of the molten glass whose said [Cl] is 0.03-0.3 mass%. The method according to any one of claims 1 to 3,
The pressure reduction defoaming method of the molten glass whose said T <_2> is 1500-1750 degreeC. The method according to any one of claims 1 to 4,
The said alkali free glass is the pressure reduction defoaming method of the molten glass containing the following components by the mass% display of the following oxide conversion.
SiO ₂ : 50-66 mass%,
Al ₂ O ₃ : 10.5-24 mass%,
B ₂ O ₃ : 0-12 mass%,
MgO: 0-8 mass%,
CaO: 0-14.5 mass%,
SrO: 0-24 mass%,
BaO: 0-13.5 mass%,
MgO + CaO + SrO + BaO: 9-29.5 mass%. The method according to any one of claims 1 to 4,
The said alkali free glass is the pressure reduction defoaming method of the molten glass containing the following components by the mass% display of the following oxide conversion.
SiO ₂ : 58-66 mass%,
Al ₂ O ₃ : 15-22 mass%,
B ₂ O ₃ : 0-12 mass%,
MgO: 0-8 mass%,
CaO: 0-9 mass%,
SrO: 3-12.5 mass%,
BaO: 0-2 mass%,
MgO + CaO + SrO + BaO: 9-18 mass%. Glass which melts a glass raw material and manufactures a molten glass, the vacuum degassing process by the pressure reduction defoaming method of the molten glass of any one of Claims 1-6, and the glass which shape | molds the pressure reduction defoaming molten glass The manufacturing method of the glass article provided with the product shaping | molding process, and having these processes in this order.

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