WO2018088503A1 - Production method for molten glass and production method for glass article - Google Patents

Abstract

Provided is a production method for molten glass in which a delay in melting of a glass raw material can be reduced. This production method for molten glass comprises melting of a glass raw material composition containing silica sand, aluminum oxide, and an alkali metal source, and thereby producing a molten glass having a glass composition containing 50 mol% or more of SiO₂, 5 mol% or more of Al₂O₃, and a total of 5 mol% or more of Li₂O, Na₂O, and K₂O, wherein the silica sand has a D90 of 450 μm or more and the difference between D90 and D10 is 350 μm or more, the aluminum oxide has a D90 of 200 μm or less, and the proportion of the volume of pores having a diameter of 0.1-5 μm is 60% or more in a pore volume distribution of a pore diameter range of 0.004-5 μm as measured by mercury intrusion.

Description

Method for producing molten glass and method for producing glass article

The present invention relates to a method for producing a molten glass and a method for producing a glass article, in particular, a method for producing an aluminosilicate glass and a method for producing a glass article.

In general, alkali aluminosilicate glass is used for a cover glass of a liquid crystal display device or the like because strength is required. In addition, such glass is required to have high chemical resistance and durability, low bubbles in the glass, high homogeneity, and high flatness, but the above-mentioned quality in the production of alkali aluminosilicate glass Is known to be more difficult than in the production of soda lime glass.
Moreover, in general, in the glass melting step, it is possible to improve the quality of glass articles and improve productivity by dissolving silica sand, which is the least soluble in the glass raw material composition, into the molten glass uniformly and quickly. It is important.
In patent document 1, as a manufacturing method of alkali aluminosilicate glass, without making the particle size of silica sand fine, the ratio of the specific surface area of the aluminum compound containing raw material contained in a glass raw material and the specific surface area of silica sand is made into a specific range. There has been proposed a method for producing an alkali aluminosilica glass that prevents undissolved residual silica sand and has few quality defects such as foam.

International Publication No. 2014/103897

However, merely reducing the unmelted silica sand in the glass raw material composition may not be sufficient for uniform melting of the entire glass raw material composition. For example, in the melting of glass, a suspended matter layer (so-called scum layer or bubble layer) may be formed on the molten glass liquid surface due to a dissolution delay due to a difference in solubility of oxides contained in the glass raw material composition. is there. The “floating material layer” is mainly composed of heterogeneous molten glass and bubbles, but the specific gravity of the heterogeneous molten glass is lower than that of the molten glass and its viscosity is high. A floating layer is formed on the surface layer.
When such a float layer is formed in a general glass melting method, the molten glass located under the float layer is used to inhibit heat input from the upper combustion space, which is a heat source for melting the glass raw material composition. The temperature rise is insufficient, and a time difference occurs between the melting of the glass material that is difficult to melt and the glass material that is easily melted. When a time difference occurs in melting, that is, when melting delay occurs in a part of the glass raw material, it becomes easier to form a heterogeneous molten glass having a specific gravity different from the composition of the target glass article, and is included in the glass raw material powder. It is easy to enclose the bubbles to be entrained in the molten glass, and the uniformity and foam quality of the glass article are likely to be deteriorated. Moreover, the problem that the productivity in a glass melting process falls by melting delay of a part of glass raw material also arises.

The present invention has been made in view of the above circumstances, and by reducing the melting delay of the glass raw material and reducing the formation of a suspended layer on the surface of the molten glass in the melting furnace, it has excellent homogeneity and is contained in the glass. It aims at providing the manufacturing method of the molten glass which can manufacture efficiently the glass article with few bubbles, and the manufacturing method of a glass article.

The present inventors investigated and examined the suspended matter layer formed on the molten glass liquid surface, and found that not only undissolved silica sand but also a large amount of undissolved aluminum oxide remained. Furthermore, the present inventors have found that by using silica sand having a large particle size distribution and using aluminum oxide having a specific particle structure, it is possible to simultaneously reduce the dissolution delay of silica sand and aluminum oxide.

The present invention has the following aspects. In the present invention, the glass component is represented by an oxide such as SiO ₂ or Al ₂ O ₃ . The content (glass composition) of each component with respect to the entire glass is expressed as a mole percentage based on the oxide.
[1] A method for producing a molten glass having the following glass composition by melting a glass raw material composition containing silica sand, aluminum oxide and an alkali metal source, wherein the silica sand has a D90 of 450 μm or more and 600 μm or less, and The difference between D90 and D10 is 350 μm or more, and the aluminum oxide has a D90 of 200 μm or less and a pore volume distribution in the pore diameter range of 0.004 to 5 μm as measured by mercury porosimetry with a pore diameter of 0.00. A method for producing molten glass, wherein the volume ratio of 1 to 5 μm is 60% or more.
Glass composition (oxide basis): SiO ₂ content is 50 mol% or more, Al ₂ O ₃ content is 5 mol% or more, and the total content of Li ₂ O, Na ₂ O, K ₂ O is 5 mol% or more.
[2] The method for producing molten glass according to [1], wherein D10 of the silica sand is 90 μm or less.
[3] The method for producing a molten glass according to [1] or [2], wherein a volume ratio of the pore diameter of 0.1 to 5 μm of the aluminum oxide is 70% or more.
[4] The method for producing molten glass according to any one of [1] to [3], wherein in the aluminum oxide, the average value of the ratio of the solid part area in the binary image of the reflected electron image of the particles is 70% or less. .
[5] In the aluminum oxide, the ratio of particles including a non-solid part in which the ratio of the solid part area in the binary image of the reflected electron image of the particle is 70% or less is 70% or more. The method for producing a molten glass according to any one of [3].
[6] The method for producing molten glass according to any one of [1] to [5], wherein a molar ratio of silica sand / aluminum oxide (oxide basis) in the glass raw material composition is 2.5 to 15.
[7] The method for producing a molten glass according to any one of [1] to [6], wherein the glass raw material composition further contains at least one of boric acid and ZrO ₂ .
[8] In the glass composition of the molten glass, the total content of SiO ₂ , Al ₂ O ₃ , Li ₂ O, Na ₂ O, and K ₂ O is 60 to 100 mol%, [1] to The method for producing a molten glass according to any one of [7].
[9] The method for producing a molten glass according to any one of [1] to [8], wherein the molten glass has the following glass composition.
Glass composition (oxide basis): SiO ₂ content 50-75 mol%, Al ₂ O ₃ content 5-20 mol%, B ₂ O ₃ content 0-20 mol%, Li ₂ The total content of O, Na ₂ O, and K ₂ O is 5 to 25 mol%, and the total content of MgO, CaO, SrO, and BaO is 0 to 20 mol%.
[10] A method for producing a glass article using the method for producing a molten glass according to any one of [1] to [9],
The manufacturing method of a glass article which has a melting process which manufactures molten glass with the said manufacturing method, a shaping | molding process which shape | molds the obtained molten glass, and a slow cooling process which anneals the glass after shaping | molding.

According to the method for producing molten glass of the present invention, the melting delay of the glass raw material can be reduced, and the formation of a floating layer on the surface of the molten glass in the melting furnace can be reduced.
According to the method for producing a glass article of the present invention, it is possible to efficiently produce a glass article with reduced melting delay of the glass raw material, excellent homogeneity, and few bubbles in the glass.

In the present invention, the “particle diameter”, “pore volume distribution of aluminum oxide by mercury intrusion method”, and “ratio of the solid area of aluminum oxide” are measured as follows.

<Measurement method of particle diameter>
“D50” is an average particle diameter represented by a 50% diameter in the integrated fraction. D50 of the glass raw material is a 50% diameter in a volume-based integrated fraction obtained by measuring the particle diameter by a laser diffraction method.
“D90” is a 90% diameter in a volume-based integrated fraction obtained by particle diameter measurement by a laser diffraction method.
“D10” is a 10% diameter in a volume-based integrated fraction obtained by particle diameter measurement by a laser diffraction method.

<Measurement method of pore volume distribution by mercury porosimetry of aluminum oxide>
Using a fully automatic pore distribution measuring device (Pore Master 60-GT, manufactured by Quanta Chrome), the pore distribution was measured under the following conditions, the horizontal axis is the pore diameter (unit: μm), and the vertical axis is dV / d. A pore volume distribution (Log differential pore volume distribution) of (logD) (unit: cm ³ / g) is obtained.
In the pore volume distribution in the pore diameter range of 0.004 to 5 μm, the ratio of the volume with the pore diameter of 0.1 to 5 μm is obtained. Specifically, the ratio of the integrated value of the pore volume in the range of the pore diameter of 0.1 to 5 μm to the integrated value of the pore volume in the range of the pore diameter of 0.004 to 5 μm was determined, and “the pore diameter of 0.1 to The ratio of the volume of 5 μm ”.
[Measurement conditions of fully automatic pore distribution measuring device]
Sample amount: about 0.3 to 0.4 g.
Pretreatment: Heat treatment at 150 ° C. for 1 hour in a dryer.
Mercury contact angle: 140 deg.
Mercury surface tension: 480 dyn / cm.

<Method for measuring the ratio of the solid area of aluminum oxide>
First, a reflection electron image of aluminum oxide is taken with an electron probe microanalyzer (EPMA). In the obtained reflected electron image, for one particle, a square or rectangle that is inscribed in the particle image and that has the largest area is defined as an area measurement area. The area measurement area is image-processed to obtain a binary image. The ratio of the area of the high-luminance region (white portion) in the area measurement area to the area (100%) of the area measurement area is obtained and is defined as “solid area ratio (unit:%)”.
“Ratio of solid part area” is obtained for 100 randomly selected particles, and the average value obtained by dividing the total by 100 is referred to as “average value of solid part area ratio (unit:%)”. To do.
Further, a particle having a “solid portion area ratio” of 70% or less is referred to as a “particle including a non-solid portion”. “Ratio of solid part area” is obtained for 100 randomly selected particles, and the percentage of “particles containing non-solid part” out of the 100 particles is “including non-solid part”. Particle ratio (unit:%) ”.
[Photographing conditions of reflected electron image by EPMA]
Voltage: 15 kV.
Current: 9.2 nA.
Contrast: 3200.
Brightness: 30-40.
Process time: 6.55 seconds.
Image size: 1280 × 960 pixels.
Magnification: 500 times.
[Image processing conditions]
Image processing software: WinRoof Ver. 6.1.
Binarization processing: Automatic binarization processing by the peak valley method.
Threshold: 31-255.
Area for measuring the area of the high-luminance region: a square or rectangle that is inscribed in one particle and has the maximum area.

<Method for producing molten glass>
The method for producing molten glass of the present invention is a method for producing a molten glass having a specific glass composition by melting a glass raw material composition containing a silicon source, an aluminum source and an alkali metal source. The silicon source is a compound that becomes SiO ₂ upon melting. The aluminum source is a compound that becomes Al ₂ O ₃ by melting.
In the present invention, the silicon source includes silica sand, and the aluminum source includes aluminum oxide.

[Silica sand]
As for the particle size distribution of the silica sand in the glass raw material composition, D90 is 450 μm or more and 600 μm or less, and the difference between D90 and D10 is 350 μm or more. That is, the silica sand contains large particles having a particle diameter of 450 μm or more and has a wide particle size distribution. By using the silica sand having such a particle size distribution, the melting delay of the glass raw material composition at the time of melting can be reduced well. D90 is preferably 470 μm or more, and more preferably 490 μm or more. The upper limit of D90 is preferably 550 μm or less, and more preferably 500 μm or less in terms of reducing the melting delay of silica sand. D10 is preferably 90 μm or less, and more preferably 80 μm or less.
The difference between D90 and D10 of silica sand is more preferably 400 μm or more, and further preferably 420 μm or more.
In this invention, you may use 1 or more types of well-known silicon sources other than silica sand in the range which does not impair the effect of this invention.

[Aluminum oxide]
The aluminum oxide in the glass raw material composition satisfies the following (a). Further, in addition to (a), the following (b) or (c) is preferably satisfied. However, in aluminum oxide, what satisfies the following (a) usually satisfies both the following (b) and the following (c).
The following (a) represents the particle structure of the aluminum oxide used in the present invention in terms of pore distribution, and the following (b) and (c) represent the particle structure as a feature in the reflected electron image of the particle. It is.
(A) In a pore volume distribution in which D90 is 200 μm or less and the pore diameter is in the range of 0.004 to 5 μm measured by mercury porosimetry, the volume ratio of pore diameters of 0.1 to 5 μm (hereinafter simply referred to as “pore diameter”). The ratio of the volume of 0.1 to 5 μm ”is 60% or more.
(B) D90 is 200 micrometers or less, and the average value of the ratio of the solid area in the binary image of the reflected electron image of particles is 70% or less.
(C) The ratio (number%) of “particles containing non-solid parts” whose D90 is 200 μm or less and the ratio of the solid part area in the binary image of the reflected electron image of the particles is 70% or less. ) Is 70% or more.
By using such aluminum oxide, the melting delay of the glass raw material composition at the time of melting can be favorably reduced.
D90 of aluminum oxide is preferably 150 μm or less, more preferably 100 μm or less, further preferably 90 μm or less, and particularly preferably 85 μm or less.
In this invention, you may use 1 or more types of well-known aluminum sources other than an aluminum oxide in the range which does not impair the effect of this invention.

In the above (a), the volume ratio of the pore diameter of 0.1 to 5 μm is preferably 70% or more, more preferably 80% or more, and still more preferably 90% or more, because the dissolution delay of aluminum oxide is reduced.

In the above (b), the average value of the ratio of the solid part area of the aluminum oxide particles is preferably 60% or less, more preferably 50% or less, and more preferably 45% or less because the dissolution delay of aluminum oxide is reduced. Further preferred. The lower limit of the average value of the ratio of the solid part area can be set as appropriate, but the volume (volume) of aluminum oxide increases as the ratio of the solid part decreases. For this reason, it is preferable to set it as the range which can be conveyed with respect to the target glass composition and can supply easily. Practically, 15% or more is preferable, and 20% or more is more preferable.
In the above (c), the ratio (number%) of the “particles containing non-solid parts” to aluminum oxide is more preferably 90% or more. Moreover, all the aluminum oxides except the aluminum oxide inevitably contained in other raw materials may be “particles containing non-solid portions”.

[Alkali metal source]
The alkali metal in the present invention refers to Na, K, and Li. The alkali metal source is a compound that becomes Na ₂ O, K ₂ O, Li ₂ O by melting. Examples of the alkali metal source include alkali metal carbonates, sulfates, nitrates, oxides, hydroxides, chlorides, and fluorides. These may be used alone or in combination of two or more. Moreover, the particle diameter is not specifically limited, A well-known alkali metal source can be used. Examples of alkali metal carbonates are preferably sodium carbonate, potassium carbonate, lithium carbonate and the like, and sodium carbonate (soda ash) is particularly suitable in terms of ease of handling.

[Alkaline earth metal source]
The glass raw material composition can contain an alkaline earth metal source in addition to the above components.
The alkaline earth metal in this specification refers to Mg, Ca, Ba, and Sr. The alkaline earth metal source is a compound that forms MgO, CaO, BaO, SrO by melting. Examples of the alkaline earth metal source include carbonates, sulfates, nitrates, oxides, hydroxides, chlorides, and fluorides of alkaline earth metals. These may be used alone or in combination of two or more. The particle diameter is not particularly limited, and a known alkaline earth metal source can be used. Also, composite carbonates such as dolomite and composite oxides such as calcined dolomite can be used.

[Boron source]
The glass raw material composition may contain a boron source. Examples of the boron source include boric acid, boric oxide (B ₂ O ₃ ), and colemanite. These may be used alone or in combination of two or more.
Examples of boric acid include orthoboric acid (H ₃ BO ₃ ), metaboric acid (HBO ₂ ), and tetraboric acid (H ₂ B ₄ O ₇ ).

[Other glass materials]
The glass raw material composition can contain compounds other than those known as glass raw materials as long as the effects of the present invention are not impaired.
Examples of the compound other than the above include tin oxide, titanium oxide, zirconium oxide, zircon, cerium oxide, antimony oxide, iron oxide, cobalt oxide, chromium oxide, copper oxide, nickel oxide and the like. These may be used alone or in combination of two or more.

[Glass raw material composition]
A glass raw material composition is prepared by mixing glass raw materials such as a silicon source, an aluminum source and an alkali metal source so as to obtain a target glass composition. The glass composition of the glass raw material composition is adjusted so as to be substantially the same as the glass composition of the target molten glass, in terms of oxides, except for components that are easily volatilized during melting. The glass composition of the molten glass is the same as the glass composition of the glass article obtained by molding the molten glass. Moreover, you may mix the clarifier and the oxide which has a clarification effect | action as an easily volatile component.
The glass composition (on oxide basis) of the molten glass in the present invention has a SiO ₂ content of 50 mol% or more, an Al ₂ O ₃ content of 5 mol% or more, and Li ₂ O, Na ₂ O, K _2. The total content of O is 5 mol% or more, and the total of these is 60 to 100 mol%.
The ratio of silica sand / aluminum oxide in the glass raw material (molar ratio based on oxide) is preferably 2.5 or more, and more preferably 4 or more, in order to prevent undissolved aluminum oxide. Moreover, 15 or less are preferable and 12 or less are more preferable when preventing the undissolved residue of silica sand.
Moreover, the glass raw material composition can further contain at least one of boric acid and ZrO ₂ in addition to silica sand, aluminum oxide, and an alkali metal source. Even a glass composition containing boric acid or ZrO ₂ having a melting point greatly different from that of silica or alumina, for example, alkali aluminosilicate glass, can prevent melting delay of raw materials and form a uniform molten glass.

The following compositions (1) to (4) may be mentioned as preferred glass compositions (100 mol% in total) of the molten glass.
Composition (1): 50 to 75 mol% of SiO ₂ , 5 to 20 mol% of Al ₂ O ₃ , 0 to 20 mol% of B ₂ O ₃ , Li ₂ O, Na ₂ O, K ₂ O 5 to 25 mol%, and the total of MgO, CaO, SrO and BaO is 0 to 20 mol%.
Composition (2): 50 to 75 mol% of SiO ₂ , 5 to 20 mol% of Al ₂ O ₃ , total of 5 to 25 mol% of Li ₂ O, Na ₂ O, K ₂ O, MgO, CaO, SrO , BaO is 0 to 20 mol%, ZrO ₂ , TiO ₂ is 0 to 5 mol%, Fe ₂ O ₃ is 0 to 5 mol%, and Co ₃ O ₄ is 0 to 0 mol%. 5 mol%.
Composition (3): SiO ₂ is 50 to 75 mol%, Al ₂ O ₃ is 5 to 20 mol%, the total of Li ₂ O, Na ₂ O, and K ₂ O is 5 to 25 mol%, and B ₂ O ₃ is 1 to 20 mol%, and the total of MgO, CaO, SrO and BaO is 0 to 25 mol%.
Composition (4): SiO ₂ is 50 to 75 mol%, Al ₂ O ₃ is 5 to 20 mol%, the total of Li ₂ O, Na ₂ O, and K ₂ O is 5 to 25 mol%, and B ₂ O ₃ is 1-15 mol%, and MgO, CaO, SrO, the sum of the BaO 0 to 15 _mol%, ZrO 2, the total of TiO ₂ is 0 to 5 mol%, the content of _Fe 2 _{O 3} is 0 to 5 mol% And the content of Co ₃ O ₄ is 0 to 5 mol%.

In the alkali aluminosilicate glass containing at least one of boric acid and ZrO ₂ , the content of B ₂ O ₃ is preferably 0 to 6 mol%, more preferably 6 to 10 mol%. The ZrO ₂ content is preferably 0 to 2 mol%, more preferably 2 to 5 mol%.
The following composition (6) is mentioned as a preferable composition in the case of further containing boric acid and optionally ZrO ₂ .
Composition (6): SiO ₂ is 50 to 75 mol%, Al ₂ O ₃ is 5 to 20 mol%, the total of Li ₂ O, Na ₂ O, and K ₂ O is 1 to 15 mol%, and B ₂ O ₃ is 1-15 mol%, and MgO, CaO, SrO, the sum of the BaO 0 to 15 _mol%, ZrO 2, the total of TiO ₂ is 0 to 5 mol%, the content of _Fe 2 _{O 3} is 0 to 5 mol% And the content of Co ₃ O ₄ is 0 to 5 mol%.

[Melting process]
The melting step for carrying out the method for producing molten glass of the present invention can be performed by a known method. Preferably, the glass raw material composition is charged into a melting furnace and melted.
In the method of melting the glass raw material composition by introducing it into the melting furnace, a suspended matter layer is formed on the molten glass liquid surface in the melting furnace due to the delayed melting of the glass raw material composition. Insufficient heating and uneven heating are likely to occur due to heat being blocked by the suspended matter layer. For this reason, the effect by improving the meltability of a glass raw material composition by applying this invention is large.
The melting furnace is not particularly limited, and may be a batch type or a continuous type.
For example, a glass raw material composition and, if necessary, a cullet having the same glass composition as that of the target molten glass is continuously charged into a melting furnace and heated to about 1600 to 1700 ° C. to be melted. And In addition, cullet is glass waste discharged | emitted in the process of glass manufacture.

<Method for producing glass article>
The glass article manufacturing method of the present invention is a method of manufacturing a glass article using the molten glass manufacturing method of the present invention.
The molten glass obtained in the above-described melting step is molded into a target shape in the molding step, and then slowly cooled in the slow cooling step as necessary. Then, a glass article is obtained by post-processing by a well-known method, such as cutting and grinding | polishing, in a post-processing process as needed.
When the glass article is plate-shaped, the molding process is performed by a known method such as a float method, a downdraw method, a fusion method, etc., and then the glass article is obtained by gradually cooling as necessary. It is done.

<Action and mechanism>
According to the present invention, in a glass raw material composition containing silica sand, aluminum oxide and an alkali metal source, silica sand having a large particle size distribution is used, and a pore volume distribution of 0.14 to 5 μm in pore volume distribution with a pore diameter of 0.004 to 5 μm. By using aluminum oxide having a particle structure in which the volume ratio of 5 μm is increased, the melting delay of silica sand and aluminum oxide can be reduced in the melting process of the glass raw material composition.
In addition, in a glass raw material composition containing silica sand, aluminum oxide and an alkali metal source, a silica structure having a large particle size distribution is used, and a particle structure in which the ratio of the solid area in the binary image of the reflected electron image of the particle is small By using the aluminum oxide having, the melting delay of silica sand and aluminum oxide can be reduced during the melting process of the glass raw material composition.

The reason is not clear, but is presumed as follows.
The above-mentioned suspended matter layer is composed of heterogeneous molten glass and bubbles. The heterogeneous molten glass has a higher concentration of SiO ₂ and Al ₂ O ₃ than the molten glass of the target composition, and is produced by the fact that silica sand and aluminum oxide are delayed in melting from the other raw material compositions in the melting process of the glass raw material composition. Further, the dissolution rate of silica sand and aluminum oxide in the heterogeneous molten glass is inferior to those in the molten glass having the target composition. Therefore, the ratio of silica sand and aluminum oxide, which have been once melted, tends to increase in the heterogeneous molten glass, and the time required until the melted silica sand and aluminum oxide are completely melted is further increased.
In contrast, according to the present invention, when the glass raw material composition is heated, the silica sand and the alkali metal source react rapidly to produce a low melting point reactant (xSiO ₂ -yA ₂ O (A represents an alkali metal). X and y represent reaction ratios))), and aluminum oxide is dissolved in the reaction product. At this time, when silica sand having a large particle size distribution is used, silica sand having a large particle diameter is relatively difficult to react, so that the ratio (x / y) of SiO _{2 in} the reaction product (xSiO ₂ -yA ₂ O) can be controlled low. For this reason, while keeping the viscosity of the reactant low, the reactivity with the aluminum oxide can be kept high by keeping the ratio (y / x) of A ₂ O in the reactant high.
Since aluminum oxide having the above specific particle structure dissolves well in such a reaction product, it is considered that the dissolution delay of aluminum oxide can be reduced. At this time, by making the particle diameter of the silica sand below a certain size, the melting delay of the silica sand can also be reduced. In this way, by reducing the melting delay of both silica sand and aluminum oxide, it is possible to reduce the formation of heterogeneous molten glass and the aggregation of silica sand and aluminum oxide that has been delayed.

Hereinafter, the present invention will be described in more detail using examples, but the present invention is not limited to these examples.
<Measurement of particle size>
Using a laser diffraction / scattering particle size distribution measuring apparatus (product name: LA-950, manufactured by Horiba, Ltd.), the particle size distribution was measured by wet laser diffraction to determine D10, D50, or D90. When the particles were aggregated in the dispersion medium, the aggregate was dispersed by ultrasonic waves, and the particle size distribution of the primary particles constituting the aggregate was measured.

<Crucible bottom temperature and suspended layer thickness measurement method (evaluation of melting delay of glass raw material composition)>
Silica sand, aluminum oxide, an alkali metal source, and other raw materials were prepared to obtain a glass raw material composition so as to obtain an alkali aluminosilicate glass having a predetermined glass composition.
The prepared glass raw material composition and cullet were mixed at a predetermined ratio, put into a crucible, and melted in the crucible. The temperature at the bottom of the crucible during glass melting was measured, and the degree of melting delay of silica sand or alumina oxide was compared.
As the crucible, an alumina crucible (product name: SSA-S, manufactured by Nikkato Corporation, inner diameter 240 mm, height 245 mm) was used.
As a melting furnace, in order to reproduce the heating state of the upper combustion space in which the molten glass is heated from above in a continuous melting furnace, a two-chamber type equipped with an operational crucible holder is equipped with a heater at the top of each furnace chamber. The large electric furnace provided was used. In the alumina crucible, the side and bottom of the crucible were covered with a heat insulating board having a thickness of 20 cm or more to block heat input from the side and bottom to the glass raw material composition in the crucible.
In order to reproduce the temperature history of the glass melting furnace in actual production, immediately after heating at 1350 ° C. for 30 minutes (dew point 50 ° C.) in the first furnace chamber, 1600 ° C., 180 ° in the second furnace chamber. It was set to be heated under the condition of minutes (dew point 50 ° C.).
In order to evaluate the degree of melting delay of the glass raw material, the crucible bottom temperature was measured by the following procedure.
First, the glass raw material composition and cullet were mixed at a predetermined ratio at room temperature and placed in a crucible. The total amount of the glass raw material composition and cullet was 2 kg in terms of glass mass.
Next, the crucible was accommodated in the first furnace chamber and heated under the above conditions, then transferred to the second furnace chamber, heated under the above conditions, and taken out from the second furnace chamber. During this time, the temperature of the outer surface of the bottom of the crucible was measured with a thermocouple, and the maximum temperature was recorded as the crucible bottom temperature.
The higher the temperature at the bottom of the crucible, the less the heat is blocked by the floating layer on the surface of the molten glass in the crucible, indicating that the temperature of the molten glass is efficiently increased by the heat from the heater.
Moreover, the crucible taken out from the second furnace chamber was gradually cooled to room temperature, and the molten glass in the crucible was solidified. After cooling and solidification, the side surface inside the crucible was observed, and the difference between the glass wet height and the glass surface height was recorded as the thickness of the suspended matter layer.

<Method for measuring the number of bubbles>
After measuring the crucible bottom temperature and suspended layer thickness, the center of the glass cooled and solidified in the crucible was cut into a cylindrical shape with an outer diameter of 35 mm, and the cut glass was cut into a 1 mm thickness to obtain a glass sample. The glass sample was mirror-polished on both sides, and an area of 2 cm ² or more equally divided with respect to the cross-sectional direction was visually observed using an optical microscope, and the number of bubbles that could be confirmed was measured.
If the melting delay of the glass raw material is small and the suspended matter layer is small, that is, if the temperature rise of the molten glass is good, the viscosity of the molten glass decreases. Because it is promoted, bubbles are easily removed during glass melting. Therefore, the smaller number of bubbles means that the melting delay of the glass raw material is suppressed.

<Glass raw material>
The following glass raw materials were used.
Silica sand: Five types of silica sands A to E shown in Table 1 were used.
Aluminum oxide: Four types of alumina S to V shown in Table 2 were used.
Alkali metal source: Soda ash (1) (D50 = 400 μm).
Magnesium source: Magnesium oxide (1) (D50 = 10 μm).
Other ingredients: Bow glass (clarifier).

[Examples 1 to 5]
Examples 1 and 2 are examples, and examples 3 to 5 are comparative examples. Silica sand, aluminum oxide, an alkali metal source, a magnesium source, and a fining agent shown in Table 3 were prepared so as to have the following glass composition (i) to obtain a glass raw material composition. The amount of fining agent added was 1.4 mol% with respect to the glass raw material composition.
With respect to the glass raw material composition of each example, the crucible bottom temperature, the float layer thickness, and the number of bubbles were measured by the above method. The mass ratio of the glass raw material composition: cullet was 50:50. The results are shown in Table 3.
<Glass composition (i)>
SiO _2: 68.0 _{mol%, Al} 2 O 3: 10.0 mol%, MgO: 8.0 _mol%, Na 2 O: 14.0 mol%. The molar ratio of SiO ₂ / Al ₂ O ₃ is 6.8.

From the results of Table 3, aluminum oxide U having a D90 of 200 μm or less, a volume ratio of pore diameters of 0.1 to 5 μm of 60% or more, and an average ratio of the solid area is 70% or less is used. In addition, Examples 1 and 2 using silica sands A and B in which D90 is 450 μm or more and the difference between D90 and D10 is 350 μm or more have a crucible bottom temperature higher than those of Examples 3 to 5 using silica sands C to E. High, thin suspended layer thickness and few bubbles. It can be seen that the melting delay of the glass raw material has been reduced.

[Examples 6 to 9]
Examples 6 to 8 are examples, and example 9 is a comparative example. Silica sand, aluminum oxide, an alkali metal source, a magnesium source, and a fining agent shown in Table 4 were prepared so as to have the glass composition (i), thereby obtaining a glass raw material composition. The amount of fining agent added is the same as in Example 1.
The glass raw material composition of each example was evaluated for the melting delay of the glass raw material and the number of bubbles by the above-described method. The mass ratio of the glass raw material composition: cullet was 35:65. The results are shown in Table 4.

From the results of Table 4, the silica sand A is used, the D90 is 200 μm or less, the volume ratio of the pore diameter is 0.1 to 5 μm is 60% or more, and the average ratio of the solid area is 70% or less. Examples 6 to 8 using the alumina S to U used in this example use the alumina V in which the volume ratio of the pore diameter is 0.1 to 5 μm is 56% and the average ratio of the solid area is 75%. Compared to Example 9, the bottom temperature of the crucible is high, the thickness of the suspended matter layer is thin, and the number of bubbles is small. It can be seen that the melting delay of the glass raw material has been reduced.
The entire contents of the specification, claims and abstract of Japanese Patent Application No. 2016-221713 filed on Nov. 14, 2016 are incorporated herein as the disclosure of the specification of the present invention. It is.

Claims (10)

1. A method for producing a molten glass having the following glass composition by melting a glass raw material composition containing silica sand, aluminum oxide and an alkali metal source,
   The silica sand has a D90 of 450 μm or more and 600 μm or less, and a difference between D90 and D10 is 350 μm or more,
   The aluminum oxide has a D90 of 200 μm or less, and the volume ratio of the pore diameter of 0.1 to 5 μm is 60% or more in the pore volume distribution in the range of pore diameters of 0.004 to 5 μm measured by mercury porosimetry. A method for producing molten glass.
   Glass composition (oxide basis): SiO ₂ content is 50 mol% or more, Al ₂ O ₃ content is 5 mol% or more, and the total content of Li ₂ O, Na ₂ O, K ₂ O is 5 mol% or more.
2. The method for producing molten glass according to claim 1, wherein D10 of the silica sand is 90 µm or less.
3. The method for producing molten glass according to claim 1 or 2, wherein a volume ratio of the pore diameter of 0.1 to 5 µm of the aluminum oxide is 70% or more.
4. The method for producing molten glass according to any one of claims 1 to 3, wherein, in the aluminum oxide, an average value of a ratio of a solid part area in a binary image of a reflected electron image of particles is 70% or less.
5. 4. The aluminum oxide according to claim 1, wherein a ratio of particles including a non-solid part in which a ratio of a solid part area in a binary image of a reflected electron image of the particle is 70% or less is 70% or more. The manufacturing method of the molten glass as described in one.
6. The method for producing molten glass according to any one of claims 1 to 5, wherein a molar ratio of silica sand / aluminum oxide (oxide basis) in the glass raw material composition is 2.5 to 15.
7. The method for producing molten glass according to any one of claims 1 to 6, wherein the glass raw material composition further contains at least one of boric acid and ZrO ₂ .
8. The total content of SiO ₂ , Al ₂ O ₃ , Li ₂ O, Na ₂ O, and K ₂ O in the glass composition of the molten glass is 60 to 100 mol%, The manufacturing method of the molten glass as described in one.
9. The method for producing molten glass according to any one of claims 1 to 8, wherein the molten glass has the following glass composition.
   Glass composition (oxide basis): SiO ₂ content 50-75 mol%, Al ₂ O ₃ content 5-20 mol%, B ₂ O ₃ content 0-20 mol%, Li ₂ The total content of O, Na ₂ O, and K ₂ O is 5 to 25 mol%, and the total content of MgO, CaO, SrO, and BaO is 0 to 20 mol%.
10. A method for producing a glass article using the method for producing a molten glass according to any one of claims 1 to 9,
    The manufacturing method of a glass article which has a melting process which manufactures molten glass with the said manufacturing method, a shaping | molding process which shape | molds the obtained molten glass, and a slow cooling process which anneals the glass after shaping | molding.