JP5194682B2 - Glass manufacturing method - Google Patents

Description

  The present invention relates to a method for producing glass, and in particular, to a method for producing soda lime glass containing an alkali metal oxide.

  Soda lime glass used as a plate glass for buildings or vehicles is made by heating and melting a raw material prepared at a predetermined blending ratio in a melting furnace, clarifying the molten glass, and then by a float method or the like. Molded into a thick glass plate. Next, this glass plate is cut into a predetermined shape to produce a plate glass for buildings or vehicles.

For refining soda lime glass, mirabilite (Na ₂ SO ₄ ) is generally used (see Patent Document 1), and a desired amount of mirabilite is contained in the raw material. By adding sodium nitrate, bubbles generated with the melting of the glass raw material are easily removed. However, the use of mirabilite as a refining agent has the following problems.
First, since the concentration of sulfur oxide (SO _x ) in the exhaust gas increases, there is a concern about adverse environmental impacts and also concerns about corrosion of manufacturing equipment. Secondly, since the generation of bubbles is promoted by the addition of mirabilite, bubbles may continue to be generated in the molding step, which is a subsequent step of the clarification step, and bubbles may remain in the glass.
From the above, there is a need for means for clarifying soda-lime glass in addition to the addition of salt cake.

Moreover, if the bubble removal from a molten glass becomes early, the size of a dissolution tank and a clarification tank can be reduced further. Therefore, in order to shorten the bubble removal time by reducing the pressure of the molten glass to increase the volume of bubbles, introduction of a vacuum degassing facility to a glass production facility has been proposed as described in Patent Document 2. By the way, the removal of the foam from the molten glass in a vacuum degassing apparatus is performed by maintaining the atmospheric pressure of the molten glass at a predetermined pressure. In such a vacuum degassing apparatus, if there is a change in the flow rate or temperature of the flowing molten glass, the atmospheric pressure of the molten glass or the liquid level of the molten glass changes. It is controlled so as to maintain a predetermined pressure by fine adjustment. However, the adjustment of the atmospheric pressure of the molten glass in the vacuum degassing equipment involves a work of raising and lowering the liquid level of the molten glass, and thus there is a problem that much labor is required.
Japanese Patent Laid-Open No. 64-69530 JP-A-9-156932

  The present invention has been made in view of the above circumstances, and provides a method for producing glass (particularly soda lime glass) that has good work efficiency and can reduce bubbles remaining in the glass after production. With the goal.

In order to achieve the above object, the present invention employs the following configuration.
The method for producing glass of the present invention is the method for producing glass in which a glass raw material containing silica sand, an alkali metal source and an alkaline earth metal source is melted, subjected to vacuum defoaming treatment, and molded. As an alkaline earth metal hydroxide, 1 to 100 mol% (MO conversion) of 100 mol% of alkaline earth metal source (MO conversion, where M is an alkaline earth metal element, the same shall apply hereinafter). ) By using what is contained, the water content in the glass is controlled, and the β-OH value (mm ⁻¹ ) of the glass is controlled to 0.05 to 0.5 (mm ⁻¹ ). Then, the liquid surface height of the molten glass inside the vacuum degassing tank is fixed, and as the glass raw material, a glass raw material that becomes glass having the following composition (1) in terms of oxide-based mass percentage is used.
_{SiO 2: 65~75%, Al 2} O 3: 0~3%, CaO: 5~15%, MgO: 0~15%, Na 2 O: 10~20%, K 2 O: 0~1.6 _{%, Li 2 O: 0~5%} , Fe 2 O 3: 0~3%, TiO 2: 0~5%, CeO 2: 0~3%, BaO: 0~5%, SrO: 0~5% , B ₂ O ₃ : 0 to 5%, ZnO: 0 to 5%, ZrO ₂ : 0 to 5%, SnO ₂ : 0 to 3%, SO ₃ : 0 to 0.5% ... Composition (1) .

According to the method for producing glass of the present invention, work efficiency is good and bubbles remaining in the glass after production can be reduced.
That is, according to the glass manufacturing method of the present invention, an alkaline earth metal hydroxide is used as a part or all of the alkaline earth metal source, and the amount of the alkaline earth metal hydroxide added is adjusted. This makes it possible to control the amount of water in the glass.
Further, according to the method for producing a glass of the present invention, an alkali metal hydroxide is used for a part or all of the alkali metal source, and the addition amount of the alkali metal hydroxide can also be adjusted. It becomes possible to control the amount of moisture.
Furthermore, as an alkaline earth metal source, an alkaline earth metal hydroxide is used as an alkaline earth metal source in an amount of 1 to 100 mol% (MO conversion) of 100 mol% (MO conversion) and an alkali metal source. alkali metal hydroxides, among alkali metal source 100 mol% _{(L 2} O equivalent), 1 to 100 mol% _{(L 2} O equivalent) by the use of those containing, controlling the water content in the glass It becomes possible to do.
And according to the manufacturing method of the glass of this invention, the defoaming appropriate pressure of a molten glass can be controlled by controlling the moisture content of glass. Conventionally, the atmospheric pressure of the molten glass in the vacuum degassing step was controlled by raising and lowering the liquid level of the molten glass.In the present invention, however, the moisture content in the glass is controlled to achieve the appropriate defoaming pressure of the molten glass. Since it can be controlled, work efficiency is good and bubbles in the molten glass can be removed without raising or lowering the liquid level of the molten glass.

Hereinafter, the manufacturing method of the glass of embodiment of this invention is demonstrated in detail.
[Glass composition]
The glass manufactured by the glass manufacturing method of this embodiment is soda-lime glass used as a plate glass for buildings or vehicles, and is expressed in terms of mass percentage based on oxide, SiO ₂ : 65 to 75%, Al _{2 O 3: 0~3%, CaO} : 5~15%, MgO: 0~15%, Na 2 O: 10~20%, K 2 O: 0~ 1.6%, Li 2 O: 0~5 _{%, Fe 2 O 3: 0~3} %, TiO 2: 0~5%, CeO 2: 0~3%, BaO: 0~5%, SrO: 0~5%, B 2 O 3: 0~5 %, ZnO: 0 to 5%, ZrO ₂ : 0 to 5%, SnO ₂ : 0 to 3%, SO ₃ : 0 to 0.5% (composition (1)).

The reasons for limiting the above components will be described below.
SiO ₂ is a network former and is essential. When the SiO ₂ content is less than 65%, the weather resistance deteriorates, and when it exceeds 75%, the viscosity becomes high and melting becomes difficult. The SiO ₂ content is more preferably 68 to 73%.

Al ₂ O ₃ is not essential, but may be contained up to 3% in order to improve the weather resistance. If it exceeds 3%, the meltability decreases. From the viewpoint of weather resistance, the Al ₂ O ₃ content is preferably 0.1% or more. The Al ₂ O ₃ content is more preferably 0.7 to 2.2%.

  CaO is a component that promotes dissolution of raw materials and improves weather resistance, and is essential. When the CaO content is less than 5%, the above-described effect is small, and when it exceeds 15%, devitrification tends to occur. The CaO content is more preferably 7.0 to 12.0%.

  MgO is a component that promotes dissolution of raw materials and improves weather resistance, so may be contained up to 15%. If it exceeds 15%, it tends to be devitrified. For the above effect, it is preferable to contain 1% or more. The MgO content is more preferably 2.0 to 7.0%.

Na ₂ O is a component that promotes dissolution of the raw material and is essential. If it is less than 10%, the above-mentioned effect is small, and if it exceeds 20%, the weather resistance is deteriorated. The Na ₂ O content is more preferably 12.0 to 15.0%.

K ₂ O is a component that promotes dissolution of the raw material, and may be contained up to 3%. If it exceeds 3%, the weather resistance deteriorates. For the above effect, it is preferable to contain 0.2% or more. The K ₂ O content is more preferably 0.4 to 1.6%.

Li ₂ O is a component that promotes dissolution of the raw material, and may be contained up to 5%. If it exceeds 5%, the weather resistance deteriorates. The Li ₂ O content is more preferably 1% or less.

Fe ₂ O ₃ is not essential, but it is a component that enhances the light absorption ability of the glass to be produced, particularly infrared absorption ability and ultraviolet absorption ability, and is also a coloring component of glass, so it can be contained up to 3%. it can. If it exceeds 3%, the radiant heat is cut off during melting, making it difficult for the heat to reach the inside, making melting difficult. For the above effect, it is preferable to contain 0.005% or more. The Fe ₂ O ₃ content is more preferably 0.010 to 1.5%.

In this specification, the total amount of iron oxide in the glass to be produced is expressed as the amount of Fe ₂ O ₃ according to the standard analysis method, but all the iron oxide present in the glass is Fe ₂ O ₃ . It does not exist in form. Usually, in addition to Fe ₂ O ₃ , divalent iron oxide (FeO) is present in the glass. When focusing on the infrared absorption ability, FeO is superior to Fe ₂ O ₃ . Therefore, in order to increase the infrared absorbing ability of the glass, it is preferable to increase the proportion (%) of FeO in the total iron represented by the following formula in the glass to be produced.
FeO / (FeO + Fe ₂ O ₃ ) × 100
Here, FeO and Fe ₂ O ₃ indicate the content ratio of FeO and Fe ₂ O ₃ converted to Fe ₂ O ₃ in the glass to be produced (in terms of oxide based mass percentage).
In the present specification, the ratio of FeO in the total iron represented by the above formula is hereinafter referred to as “the ratio of FeO in the total iron”.

  The glass produced by the production method of the present embodiment preferably has a ratio of FeO in the total iron of 20 to 60%. If the ratio of FeO in the total iron is 20 to 60%, the produced glass is excellent in infrared absorption ability. The proportion of FeO in the total iron is more preferably 25 to 55%, and further preferably 30 to 50%.

TiO ₂ is not essential, but can be contained up to 5% in order to adjust the light transmittance of the glass to be produced, specifically, the visible light transmittance and the ultraviolet transmittance. Even if it exceeds 5%, it no longer contributes to the adjustment of the light transmittance, which is undesirable in terms of cost. Further, when glass is formed by the float process, TiO ₂ reacts with molten tin in the float bath, and a glass having a desired color tone cannot be obtained. In the case of adjusting the light transmittance, it is preferably contained in an amount of 0.05 to 4.5%, more preferably 0.1 to 4.2%.

CeO ₂ is not essential, but can be incorporated up to 3% in order to increase the ultraviolet absorbing ability of the glass to be produced. If it exceeds 3%, a glass-like defect tends to occur. In order to raise the ultraviolet absorptivity of the glass to be produced, 0.05 to 2.0% is preferably contained, and 0.1 to 1.8% is more preferably contained.
BaO and SrO are not essential, but can be incorporated up to 5% in order to improve solubility. If it exceeds 5%, it tends to be devitrified. The content of BaO and SrO is preferably 2% or less.

ZnO is not essential, but can be incorporated up to 5% for improving weather resistance. If it exceeds 5%, the coefficient of thermal expansion of the glass decreases, so that it is difficult to strengthen the air cooling. The ZnO content is preferably 1% or less.
ZrO ₂ is not essential, but can be incorporated up to 5% in order to improve the elastic modulus of the glass. If it exceeds 5%, it will be difficult to dissolve the raw materials. The content of ZrO ₂ is preferably 1% or less.

B ₂ O ₃ is not essential, but may be contained up to 5% in order to improve solubility. If it exceeds 5%, the softening point becomes low. Preferably it is 1% or less.
SnO ₂ is not essential, but can be incorporated up to 3% for the purpose of adjusting the proportion of FeO in the total iron. If it exceeds 3%, a glass-like defect tends to occur. The SnO ₂ content is preferably 1% or less.

In this embodiment, since the proper defoaming pressure of the molten glass is controlled by controlling the amount of water in the glass, it is not necessary to use SO ₃ (as mirabilite) as a clarifier. However, the raw material contains SO ₃ as an inevitable impurity. In addition, since SO ₃ has an effect of increasing the solubility of the raw material, a small amount of SO ₃ may be contained in order to increase the solubility. In this case, the SO ₃ content is preferably 0.5% or less. However, it is preferable that SO ₃ does not contain other than inevitable impurities in the glass to be produced.
In addition, in the formula (2) described later, [SO ₃ ] indicating the SO ₃ content ratio of the glass is obtained by forming a molten glass before decompression defoaming into a plate shape, similarly to [β-OH] described later. It is a numerical value obtained using. [SO ₃ ] calculated | required by the above is a value substantially the same as the numerical value calculated | required using what shape | molded the molten glass after pressure reduction degassing in plate shape.

  In addition to the above components, the glass according to the present embodiment includes F, Cl, V, Cr, Mn, Co, Ni, Cu, Se, Mo, Ag, In, Te, La, Pr, Nd, Er, and W. And at least one selected from Au may be contained as an optional component.

  F and Cl can be contained for the purpose of promoting dissolution of the raw materials. Further, V, Cr, Mn, Co, Cu, Mo, Ag, In, Te, La, Pr, Nd, Er, W, and Au can be contained as light absorbing components.

  Ni can be contained as a coloring component of glass in the form of NiO. If Ni exceeds 0.5%, NiO reacts with molten tin in the float bath, and there is a possibility that a glass having a desired color tone cannot be obtained. For the above-mentioned effects, 0.005 to 0.3% is preferably contained, and 0.05 to 0.1% is more preferably contained.

  Se can be contained up to 0.05% as a coloring component of the glass. If it exceeds 0.05%, it will no longer contribute to the color tone correction, which is undesirable in terms of cost. For the above-mentioned effect, it is preferable to contain 0.01% or less, and more preferably 0.005% or less.

The glass produced by the glass production method of the present embodiment contains moisture as an essential component in addition to the above components. Moisture is a clarification component of glass that enlarges bubbles and increases the rising speed of bubbles in a vacuum degassing step described later. The moisture in the glass originates from hydroxyl groups in the raw material, moisture in the raw material, moisture in the atmosphere in which the glass is dissolved, and in particular, due to hydroxyl groups in the raw material.
In the glass manufacturing method of the present embodiment, the β-OH value of glass is used as an indicator of the water content in the glass. The β-OH (mm ⁻¹ ) value of glass is obtained by measuring the absorbance of a glass sample with respect to light having a wavelength of 2.75 to 2.95 μm and dividing the maximum value β _max by the thickness (mm) of the sample. Can be sought. In addition, what shape | molded the molten glass before pressure reduction defoaming in plate shape is used for the glass sample used when calculating | requiring a beta-OH value.

The β-OH value of the glass is preferably 0.05 to 0.5 mm ⁻¹ . The β-OH value is governed by the amount of water in the raw material, the water vapor concentration in the melting tank, and the residence time of the molten glass in the melting tank. When the raw material and the combustion atmosphere are constant, the β-OH value depends on the staying time and increases with an increase in the staying time. In order to melt the glass homogeneously, a certain residence time is required in the melting tank. If the glass is short, the glass becomes inhomogeneous, and if it is too long, the fuel is wasted. If the β-OH value of the glass is within the above range in a general industrial raw material and natural gas or heavy oil combustion atmosphere, the residence time in the melting tank is appropriate, and a homogeneous molten glass can be obtained efficiently. The β-OH value of the glass is more preferably 0.15 to 0.4 mm ⁻¹ .

In addition, the moisture content ratio W (wt%) of glass can also be calculated | required from the beta-OH value of glass using a following formula.
W = 18 × [β-OH] / (ερ)
In the above formula, ρ represents the density (g / cm ³ ) of the glass sample. ε represents a molar extinction coefficient (l / mol · cm). Although the molar extinction coefficient varies depending on the glass composition, generally, in the case of soda lime glass, ε = 73 (l / mol · cm).
Therefore, when the β-OH value of the glass is 0.05 to 0.5 mm ⁻¹ , the moisture content W of the glass is 0.005 to 0.049 wt%.
However, as described above, the β-OH value of the glass is a numerical value obtained by using a molten glass before decompression defoaming formed into a plate shape, so the moisture content W of the glass obtained by the above formula is: It is a numerical value related to the glass before the vacuum degassing, and is slightly different from the water content ratio W ′ of the glass after the vacuum degassing. When the moisture content W of the glass before vacuum degassing is 0.005 to 0.049 wt%, the moisture content W ′ of the glass after vacuum degassing is usually 0.004 to 0.045 wt%.

As described above, the β-OH value of glass is governed by the amount of water in the raw material, the water vapor concentration in the melting tank, and the residence time of the molten glass in the melting tank, but is particularly governed by the amount of water in the raw material. The Therefore, in order to adjust the β-OH value of the glass, the amount of hydroxyl groups in the raw material may be controlled. For example, when the β-OH value of a glass using dolomite ((Ca, Mg) CO ₃ ) as an alkaline earth metal source is about 0.2 mm ⁻¹ , the total amount of dolomite is converted to calcium hydroxide and hydroxide. By replacing with magnesium, the β-OH value can be increased to about 1.2 times. In addition, when the β-OH value of the glass using an alkali metal carbonate as an alkali metal source was about 0.2 mm ⁻¹ , the alkali metal carbonate was replaced with a hydroxide, so that β− The OH value can be increased to about 3 times.

Moreover, it becomes possible to reduce the glass forming temperature by increasing the β-OH value of the glass. For example, when the β-OH value is increased from 0.15 mm ⁻¹ to 0.30 mm ⁻¹ , the molding temperature decreases by about 5 to 10 ° C. Therefore, it is possible to reduce the molding temperature when the plate-like glass produced by the production method of the present embodiment is formed into a curved glass, thereby improving the moldability.

The glass of this embodiment is manufactured by melting and molding a glass raw material containing silica sand, an alkaline earth metal source and an alkali metal source. Moreover, it manufactures also by fuse | melting and shape | molding the glass raw material containing a silica sand, an alkaline-earth metal source, an alkali metal source, and an aluminum source. More specifically, for example, it is manufactured as follows.
(I) Silica sand, alkaline earth metal source and alkali metal source, or quartz sand, alkaline earth metal source, alkali metal source and aluminum source, and optionally Al ₂ O ₃ , Fe ₂ O ₃ , TiO ₂ , CeO _A glass raw material is prepared by mixing a boron source such as ₂ or B ₂ O ₃ , ZnO, ZrO ₂ and SnO ₂ in such a ratio as to achieve a target glass composition.
(Ii) The glass raw material and, if necessary, cullet having the same composition as the target glass composition are continuously charged into the melting kiln from the glass raw material charging port of the melting kiln, and 1050 ° C. to 1350 ° C. To obtain molten glass. The cullet is glass waste discharged in the process of manufacturing glass.
(Iii) The molten glass is introduced into a vacuum degassing equipment and degassed under vacuum.
(Iv) The molten glass after the vacuum degassing step is molded to have a predetermined thickness by a known molding method such as a float method.
(V) After the formed glass ribbon is gradually cooled, it is cut into a predetermined size to obtain plate-like glass.

Hereinafter, silica sand and the like used for the glass raw material will be described.
(Silica sand)
The average particle diameter of the silica sand is preferably 15 to 500 μm, and more preferably 20 to 300 μm.
By setting the average particle diameter of the silica sand to 15 μm or more, aggregation of the silica sand can be suppressed, so that a glass having few bubbles and excellent in homogeneity and flatness can be obtained. Further, when the average particle size of the silica sand is 500 μm or less, the silica sand is easily melted uniformly, so that a glass having less bubbles and more excellent uniformity and flatness can be obtained. The average particle diameter is preferably measured by, for example, a laser diffraction / scattering method.

(Alkaline earth metal source)
An alkaline earth metal compound can be used as the alkaline earth metal source. Here, examples of the alkaline earth metal include any one element or two or more elements of Mg, Ca, Sr, and Ba. Specific examples of the alkaline earth metal compound include carbonates such as MgCO ₃ , CaCO ₃ , BaCO ₃ , SrCO ₃ , (Mg, Ca) CO ₃ (dolomite), MgO, CaO, BaO, SrO and the like. Oxides and hydroxides such as Mg (OH) ₂ , Ca (OH) ₂ , Ba (OH) ₂ , Sr (OH) ₂ can be exemplified, but in the present invention, some or all of the alkaline earth metal source Hydroxide is used. By using the alkaline earth metal hydroxide as the alkaline earth metal source, as described above, the water content (β-OH value) in the glass is arbitrarily set within the range of 0.05 to 0.5 mm ^−1. Can be controlled.

The content of the alkaline earth metal hydroxide is 1 to 100 mol% (MO conversion) of 100 mol% (MO conversion, where M is an alkaline earth metal element) of the alkaline earth metal source. A range is preferred. If the amount of hydroxide added is less than 1 mol%, the amount of water in the glass (β-OH value) is hardly affected, which is not preferable. As the molar ratio of hydroxide in the alkaline earth metal source increases, the amount of water in the glass (β-OH value) tends to increase.
Further, if the amount of hydroxide added is less than 1 mol%, when the glass raw material is melted, the unmelted amount of the SiO ₂ component contained in the silica sand increases, and this unmelted SiO ₂ is added to the glass melt. When bubbles are generated, they are taken into the bubbles and gather near the surface of the glass melt. As a result, a difference in the composition ratio of SiO ₂ occurs between the surface layer of the glass melt and the portion other than the surface layer, which is not preferable because the uniformity of the glass decreases and the flatness also decreases.

Specific examples of the alkaline earth metal source include a mixture of (Mg, Ca) CO ₃ (dolomite) and an alkaline earth metal hydroxide, a mixture of an alkaline earth metal hydroxide and a carbonate, Alkaline earth metal hydroxides alone can be used. As the carbonate, it is preferable to use one or more of MgCO ₃ , CaCO ₃ and (Mg, Ca) CO ₃ (dolomite). As the hydroxide, it is preferable to use either one or both of Mg (OH) _{2 and} Ca (OH) ₂ .

(Alkali metal source)
An alkali metal compound can be used as the alkali metal source. Here, examples of the alkali metal include Na and, if necessary, one or both of K and Li. Specific examples of the alkali metal compound include oxides such as Na ₂ O, K ₂ O, and Li ₂ O, carbonates such as Na ₂ CO ₃ , K ₂ CO ₃ , and Li ₂ CO ₃ , NaOH, Although hydroxides, such as KOH and LiOH, can be illustrated, in this invention, a hydroxide can be used for a part or all of an alkali metal source. By using an alkali metal hydroxide as the alkali metal source, the water content (β-OH value) in the glass can be arbitrarily controlled within the range of 0.05 to 0.5 mm ⁻¹ as described above. it can.
Specifically, for example, a mixture of an oxide and a hydroxide, a mixture of a carbonate and a hydroxide, a hydroxide alone, or the like can be used as the alkali metal source.

The content of the alkali metal hydroxide is in the range of 1 to 100 mol% (L ₂ O conversion) in 100 mol% of the alkali metal source (L ₂ O conversion, where L is an alkali metal element). preferable. If the amount of hydroxide added is less than 1 mol%, the amount of water in the glass (β-OH value) is hardly affected, which is not preferable. As the molar ratio of hydroxide in the alkali metal source increases, the amount of water (β-OH value) in the glass tends to increase.

(Boron source)
Next, boron compounds as a boron source include orthoboric acid (H ₃ BO ₃ ), metaboric acid (HBO ₂ ), tetraboric acid (H ₂ B ₄ O ₇ ), anhydrous boric acid (anhydrous B ₂ O ₃ ), and the like. Is mentioned.
In ordinary glass production, anhydrous boric acid is used because it is inexpensive and easily available.
In the case of using anhydrous boric acid as a source of boron, of boron source 100 _{wt% (B} 2 _{O 3} conversion), it is preferable to use those containing 10 to 100 _{wt% (B} 2 _{O 3} conversion). By setting the boric anhydride to 10% by mass or more, aggregation of the glass raw material is suppressed, and an effect of reducing bubbles, homogeneity, and improving flatness can be obtained. A more preferable range of boric anhydride is in the range of 20 to 100% by mass. As a boron compound other than boric anhydride, orthoboric acid is preferable because it is inexpensive and easily available.

(Other ingredients)
Examples of other raw materials include Al ₂ O _3, Fe ₂ O ₃ , TiO ₂ , CeO ₂ , ZnO, ZrO ₂ and SnO ₂ . Moreover, in order to improve meltability, clarity, and moldability, F and Cl may be contained.

(Glass raw material)
The glass raw material is a powdery mixture in which the respective raw materials are mixed.
The composition of the glass raw material is set so as to be a glass having a target composition. The composition of the glass raw material is preferably a composition that becomes the glass of the above composition (1).

And, if necessary, cullet having the same composition as the target glass composition is continuously fed into the melting kiln from the glass raw material charging port of the melting kiln, 1050 to 1350 ° C. or higher To make molten glass.
At this time, fuel such as heavy oil or natural gas is burned to form a heat source. Fuels such as heavy oil and natural gas may be mixed with oxygen and burned, or may be mixed with air and burned. The water content (β-OH value) of the glass can also be adjusted by controlling the combustion method. When it is desired to increase the β-OH value of the glass, it is preferable that the fuel and oxygen are mixed and burned. In this case, the amount of water vapor contained in the gas after combustion increases. Specifically, the amount of water vapor contained in the gas after combustion is about 2.3 times that of the case where it is mixed with air and combusted. Therefore, when it mixes with oxygen and burns, compared with the case where it mixes with air and combusts, about 2.3 times as much water vapor | steam will exist in the atmosphere of a dissolution tank. On the other hand, when it is desired to lower the β-OH value of the glass, the water vapor concentration in the atmosphere of the melting tank may be lowered, or the residence time of the molten glass in the melting tank may be shortened. As a method for lowering the water vapor concentration in the dissolution tank, there is a method in which a fuel such as heavy oil or natural gas is mixed with air and burned. However, in the combustion method, the β-OH value of the glass can be changed greatly, but it is difficult to fine-tune. Moreover, when using an electric furnace to heat-melt a raw material, the beta-OH value of glass can also be adjusted by adjusting the water vapor partial pressure in an electric furnace.

  The molten glass melted in the melting tank is sequentially sent out to the vacuum degassing equipment. In the vacuum degassing equipment, for example, a cylindrical vacuum vacuum degassing tank is housed and arranged in the vacuum housing so that its long axis is oriented in the horizontal direction. A rising pipe oriented in the vertical direction is attached to the lower surface of one end of the vacuum degassing tank, and a lowering pipe is attached to the lower surface of the other end. A part of the riser pipe and the downcomer pipe is located in the decompression housing.

The ascending pipe communicates with the vacuum degassing tank and is an introduction means for introducing the molten glass from the melting tank into the vacuum degassing tank. For this reason, the lower end portion of the rising pipe is fitted into the opening end of the upstream pit and is immersed in the molten glass in the upstream pit.
The downcomer communicates with the vacuum degassing tank, and is a deriving means for lowering the molten glass after the vacuum degassing from the vacuum degassing tank and leading it to the next processing tank. For this reason, the lower end portion of the downcomer is fitted into the opening end of the downstream pit and is immersed in the molten glass in the downstream pit.
In the decompression housing, a heat insulating material such as a heat insulating brick is provided around the decompression defoaming tank, the riser pipe, and the downcomer pipe to insulate them.

In the vacuum degassing equipment, the molten glass is vacuum degassed under an atmosphere of a bubble growth starting pressure P _eq (kPa) or less represented by the following formula (2).
P _eq = −80.8 + 98.2 × [β-OH] + 68.0 × [SO ₃ ] + 0.0617 × T (2)
Here, in formula (2), [β-OH] represents the β-OH value (mm ⁻¹ ) of the glass, and [SO ₃ ] represents the SO ₃ content ratio (mass percentage based on oxide) of the glass. T) is the temperature of the molten glass and indicates the temperature (° C.) of the molten glass circulating in the vacuum degassing vessel. Note that the bubble growth starting pressure depends on [β-OH] and [SO ₃ ] so that when each component falls below a certain pressure depending on the concentration, the bubble growth is affected. It is presumed that it is.

Here, the bubble growth starting pressure P _eq is defined as follows.
When the atmosphere in which vacuum degassing is performed under a constant temperature condition (usually, the atmosphere in the vacuum degassing tank of the vacuum degassing equipment) is reduced, it exists in the molten glass existing in the atmosphere. Bubble volume (bubble diameter) increases according to Boyle's law. However, when the atmosphere is depressurized to a certain pressure, the volume of bubbles in the molten glass (the diameter of the bubbles) suddenly increases outside Boyle's law. This pressure is referred to as a bubble growth starting pressure _Peq . The bubble growth starting pressure P _eq can be obtained by the following procedure.
In order to reproduce the atmosphere in which vacuum degassing is performed, a crucible containing a glass raw material is placed in a vacuum vacuum container. The crucible is heated to a predetermined temperature (for example, 1300 ° C.) to melt the glass. After the glass is completely melted, the diameter of bubbles in the molten glass is observed while decompressing the inside of the vacuum decompression vessel. In order to observe the diameter of the bubbles in the molten glass, for example, the bubbles in the molten glass may be photographed using a CCD camera from a viewing window provided in the vacuum decompression device.
As 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 the vacuum decompression container is depressurized to a certain pressure, the diameter of bubbles in the molten glass deviates from Boyle's law and increases rapidly. The degree of decompression in the vacuum decompression container at this time is defined as a bubble growth start pressure P _eq .

The above procedure was performed while changing the β-OH value and temperature of the molten glass, and the bubble growth starting pressure P _eq was derived as a regression equation of the β-OH value and temperature of the molten glass as shown in the above formula (2). It was.

H ₂ O, O ₂ , CO _2, etc. dissolved in the molten glass by defoaming the molten glass under reduced pressure in an atmosphere below the bubble growth starting pressure P _eq (kPa) represented by the above formula (2) The inflow speed of the gas component into the bubbles is remarkably increased, the bubble radius is increased, and the rising speed of the bubbles is increased. At this time, H ₂ O is dominant among the gas components described above. As a result, the time for the bubbles to reach the surface of the molten glass is remarkably shortened, and vacuum degassing is promoted.

When carrying out the vacuum degassing, the air in the vacuum housing is exhausted from the outside by a vacuum pressure reducing means (not shown) such as a vacuum pump. Thereby, the air in the vacuum degassing tank accommodated in the vacuum housing is indirectly exhausted, and the inside of the vacuum degassing tank is depressurized. By such a procedure, the atmospheric pressure P inside the vacuum degassing tank is adjusted to be equal to or lower than the bubble growth starting pressure _Peq . However, in the vacuum degassing apparatus, if the flow rate or temperature of the flowing molten glass varies, the atmospheric pressure of the molten glass, the liquid level of the molten glass, and the like change. The degree of decompression in the vacuum degassing tank is proportional to the height of the liquid level in the vacuum degassing tank from the liquid level of the molten glass in the upstream pit and downstream pit. It is necessary to compensate for this and return it to a normal state. As a means for this, it is common to control the height of the liquid surface of the molten glass inside the vacuum degassing tank by raising and lowering it.
In this embodiment, on the other hand, in a state of fixing the height of the liquid surface of the molten glass inside the vacuum degassing vessel, i.e. in a state of fixing the vacuum degassing vessel body, the beta-OH value of the glass By controlling the bubble growth starting pressure P _eq , the degree of pressure reduction in the vacuum degassing tank can be controlled.

As described above, the β-OH value of the glass is preferably 0.05 to 0.5 mm ⁻¹ . The bubble growth starting pressure P _eq depends on the β-OH value (mm ⁻¹ ) of the glass and is obtained by the regression equation (2) of the β-OH value and temperature of the molten glass. When the OH value is controlled in the range of 0.05 to 0.5 mm ⁻¹ , an effect equivalent to the decompression effect of 98.2 × 0.5 = 49.1 kPa (36.7 mmHg) can be obtained from the equation (2). I understand that. Therefore, the amount of alkali metal or alkaline earth metal hydroxide in the glass raw material is adjusted to control the β-OH value in the glass in the range of 0.1 to 0.5 mm ⁻¹ , and the liquid level of the molten glass Bubbles in the molten glass can be efficiently removed without raising or lowering the level.

In addition, the temperature of the molten glass G which distribute | circulates the inside of a vacuum degassing tank is not necessarily constant, and changes with the site | parts in a vacuum degassing tank. For example, the temperature of the molten glass differs between the upstream side and the downstream side of the vacuum degassing tank. In this invention, the temperature T of Formula (2) is the average temperature of the molten glass G which distribute | circulates the inside of a vacuum degassing tank. The average temperature means the temperature upstream of the vacuum degassing tank (for example, the temperature of the molten glass entering the vacuum degassing tank from the riser) and the temperature downstream (for example, from the vacuum degassing tank to the downcomer). The average value with the temperature of the molten glass entering.
The average temperature of the molten glass flowing in the vacuum degassing tank is preferably 1050 to 1350 ° C. In the case of the glass composition specified above, the viscosity of the molten glass at a temperature of 1050 to 1350 ° C. is 200 to 6500 poise. If the viscosity of the molten glass is within the above range, the flow of the molten glass in the vacuum degassing tank will not be remarkably slowed, and the molten glass will not leak out from the joint portion of the vacuum degassing tank.

  The molten glass G that has been circulated in the vacuum degassing tank and degassed under reduced pressure moves from the downstream pipe to the next processing tank (not shown) via the downstream pit. Thereafter, it is processed into a glass sheet for buildings or vehicles by a predetermined forming method, for example, a float forming method, a roll-out forming method, a fusion forming method or the like.

[Experiment 1]
In terms of mass percentage based on oxide, SiO ₂ : 70.9%, Al ₂ O ₃ : 1.8%, CaO: 7.6%, MgO: 3.7%, Na ₂ O: 12.9%, K ₂ O: 0.6%, Li ₂ O: 0%, Fe ₂ O ₃ : 0.60%, TiO ₂ : 0.40%, CeO ₂ : 1.50%, BaO: 0%, SrO: 0 %, B ₂ O ₃ : 0%, ZnO: 0%, ZrO ₂ : 0%, SnO ₂ : 0%, SO ₃ : 0.006 to 0.04% soda lime glass having a composition, Silica sand, alkaline earth metal source, alkali metal source and other raw materials were adjusted to obtain glass raw materials. As the alkaline earth metal source, as shown in Table 1, one or more alkaline earth metal compounds of Mg (OH) ₂ , Ca (OH) ₂ , and dolomite ((Mg, Ca) CO ₃ ) are used. It was. As the alkali metal source, an alkali metal carbonate was used.

  Next, a glass raw material having an amount of 250 g after vitrification was placed in a bottomed cylindrical platinum rhodium crucible having a height of 90 mm and an outer diameter of 70 mm. The crucible is put into a heating furnace, heated at 1500 ° C. (glass viscosity η corresponds to log η = 2.5) for 4 hours while blowing air with a dew point of 80 ° C. from the side of the heating furnace, and stirred for 1 hour. The glass raw material was melted. After cooling the molten glass together with the crucible, a sample was cut out from the central portion of the glass in the crucible with dimensions of 24 mm in length, 35 mm in width, and 1 mm in thickness.

The β-OH value was measured for the sample taken out. The β-OH value was measured by measuring the absorbance of the sample with respect to light having a wavelength of 2.75 to 2.95 μm, and dividing the maximum value β _max by the thickness (1 mm) of the sample. The results are shown in Table 1.
Further, the composition ratio of SO _{3 in} the glass was measured by a fluorescent X-ray method. Further, the bubble growth starting pressure P _eq was determined by substituting the β-OH value and the composition ratio of SO ₃ into the above equation (2). These results are also shown in Table 1.

As is apparent from the results in Table 1, as the amount of hydroxide in the alkaline earth metal compound increases, the value of β-OH value increases, and the bubble growth starting pressure P _eq increases accordingly. I understand. Therefore, it can be seen that the β-OH value and the bubble growth starting pressure P _eq can be controlled by adjusting the amount of hydroxide in the alkaline earth metal compound. It is also possible to control the β-OH value and the bubble growth starting pressure P _eq by adjusting the amount of hydroxide in the alkali metal compound.

And according to the manufacturing method of the glass of this invention, the starting pressure _Peq of the bubble growth in a molten glass can be controlled by controlling the moisture content of glass. Atmospheric pressure P of the molten glass in the vacuum degassing step is less than the start pressure P _eq foam growth, it is necessary to hold the defoaming proper pressure, conventionally the atmosphere pressure P by lifting the liquid level of the molten glass In the present invention, by controlling the amount of water in the glass and controlling the bubble growth starting pressure _Peq itself, the atmospheric pressure P is appropriately defoamed without raising or lowering the liquid level of the molten glass. Thus, bubbles in the molten glass can be efficiently removed. Thereby, the structure of the vacuum degassing apparatus can be simplified.
Moreover, according to the manufacturing method of the glass of this invention, it becomes possible to reduce the shaping | molding temperature of glass by raising the beta-OH value of glass. For example, when the β-OH value is increased from 0.15 mm ⁻¹ to 0.30 mm ⁻¹ , the molding temperature decreases by about 10 ° C. Therefore, when the plate-like glass manufactured by the manufacturing method of the present embodiment is processed and formed into curved glass, the processing forming temperature can be lowered, and the processing moldability can be improved.

Claims (3)

In the glass manufacturing method for melting glass raw material containing silica sand, alkali metal source and alkaline earth metal source, subjecting to vacuum defoaming treatment, and molding,
As the alkaline earth metal source, an alkaline earth metal hydroxide is selected from 1 to 100 mol% of an alkaline earth metal source (in terms of MO. M is an alkaline earth metal element, the same shall apply hereinafter). A method for producing glass, characterized by controlling the amount of water in glass by using 100 mol% (in terms of MO).
The β-OH value (mm ⁻¹ ) of the glass is controlled to 0.05 to 0.5 (mm ⁻¹ ),
With the liquid level of the molten glass inside the vacuum degassing tank fixed,
The glass manufacturing method using the glass raw material used as the glass raw material used as the glass of the following composition (1) by the mass percentage display of an oxide basis.
_{SiO 2: 65~75%, Al 2} O 3: 0~3%, CaO: 5~15%, MgO: 0~15%, Na 2 O: 10~20%, K 2 O: 0~1.6 _{%, Li 2 O: 0~5%} , Fe 2 O 3: 0~3%, TiO 2: 0~5%, CeO 2: 0~3%, BaO: 0~5%, SrO: 0~5% , B ₂ O ₃ : 0 to 5%, ZnO: 0 to 5%, ZrO ₂ : 0 to 5%, SnO ₂ : 0 to 3%, SO ₃ : 0 to 0.5% ... Composition (1) . The β-OH value (mm ⁻¹ ) of the glass is controlled to 0.3 to 0.5 (mm ⁻¹ ), and the method for producing glass according to claim 1 . Wherein the glass raw material, K _{2 O} as represented by mass percentage based on oxides is a glass material comprising a 0.4 to 1.6% of the glass, the production method of glass according to claim 1 or claim 2.