Method for manufacturing molten glass and method for manufacturing glass articles

Abstract

To provide a method for manufacturing molten glass that can further reduce the delay in melting of the glass raw material composition during the glass melting process. [Solution] A method for producing molten glass having a glass composition containing SiO2 and Al2O3 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 more than 600 μm, and the aluminum oxide has a D90 of 200 μm or less. The glass composition preferably has an oxide-based content of SiO2 of 50 mol% or more, an Al2O3 content of 5 mol% or more, and a total content of Li2O, Na2O, and K2O of 5 mol% or more.

Description

Technical Field

[0001] The present invention relates to a method for producing molten glass and a method for producing a glass article.

Background Art

[0002] Cover glass for liquid crystal display devices and the like is required to have strength. For this reason, alkali aluminosilicate glass is generally used for cover glass. Furthermore, cover glass is required to have high chemical resistance and durability, few bubbles in the glass, high homogeneity, and high flatness. However, it is known that it is more difficult to obtain a quality that satisfies all of the above characteristics in the production of alkali aluminosilicate glass than in the production of soda-lime glass.

[0003] Also, in the glass melting process, quickly and uniformly melting a glass raw material composition into molten glass is important for improving the quality of glass articles and for improving productivity.

[0004] For example, Patent Document 1 proposes a method for manufacturing molten glass and glass articles that can efficiently produce glass articles with excellent homogeneity and few bubbles in the glass by reducing the delay in melting of glass raw materials and reducing the formation of a floating layer on the surface of the molten glass in the melting furnace. More specifically, Patent Document 1 describes a method for manufacturing molten glass, in which a glass raw material composition containing silica sand, aluminum oxide, and an alkali metal source is melted to produce molten glass having a glass composition (oxide basis) in which the SiO2 content is 50 mol% or more, the Al2O3 content is 5 mol% or more, and the total content of Li2O, Na2O, and K2O is 5 mol% or more. Patent Document 1 describes silica sand contained in the glass raw material composition having a D90 of 450 μm or more and 600 μm or less, and a difference between D90 and D10 of 350 μm or more. Furthermore, Patent Document 1 describes an aluminum oxide contained in a glass raw material composition in which the D90 is 200 μm or less, and in the pore volume distribution in the range of pore diameters from 0.004 to 5 μm measured by the mercury intrusion method, the proportion of the volume of pores with a diameter of 0.1 to 5 μm is 60% or more. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Patent No. 6981426 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] However, conventional methods for manufacturing molten glass have not been able to adequately suppress the delayed melting of the glass raw material composition during the glass melting process. This delayed melting of the glass raw material composition during the glass melting process causes a layer of suspended matter to form on the surface of the molten glass in the melting furnace, reducing the homogeneity, bubble quality, and productivity of the glass articles. As a result, glass articles manufactured using conventional methods for manufacturing molten glass sometimes contained many bubbles in the glass, or had insufficient uniformity and productivity.

[0007] Furthermore, in the method for manufacturing molten glass described in Patent Document 1, it was necessary to use aluminum oxide contained in the glass raw material composition such that, in the pore volume distribution in the range of pore diameters from 0.004 to 5 μm measured by the mercury intrusion method, the proportion of the volume of pores with a diameter of 0.1 to 5 μm was 60% or more. Therefore, there was a disadvantage in that there were few options for aluminum oxide that could be used as a raw material for the glass raw material composition.

[0008] This invention has been made in view of the above circumstances, and aims to provide a method for manufacturing molten glass that can further reduce the delay in melting of the glass raw material composition during the glass melting process. Furthermore, the present invention aims to provide a method for manufacturing glass articles that uses a method for manufacturing molten glass that can reduce the delay in melting of the glass raw material composition during the glass melting process. [Means for solving the problem]

[0009] The inventors of the present invention have diligently studied the following methods to solve the above problems and reduce the delay in melting of the glass raw material composition during the glass melting process. First, the inventors investigated the suspended solids layer formed on the surface of the molten glass. As a result, it was found that the heterogeneous molten glass forming the suspended solids layer contained higher concentrations of SiO2 and Al2O3 than the molten glass of the target composition. From this, it is presumed that silica sand and aluminum oxide that did not dissolve quickly during the melting process of the glass raw material composition generated heterogeneous molten glass, which in turn generated the suspended solids layer.

[0010] Therefore, the inventors focused on the particle size of silica sand and aluminum oxide contained in the glass raw material composition and conducted extensive research to reduce the delayed dissolution of silica sand and aluminum oxide. Typically, when attempting to mitigate the delayed dissolution of a specific component in a glass raw material composition, it is thought that removing larger particles of the component causing the delayed dissolution would suffice.

[0011] However, contrary to expectations, the inventors discovered that it is possible to produce molten glass having a specific glass composition by melting a glass raw material composition containing silica sand with large particles having a D90 of over 600 μm and aluminum oxide with a D90 of 200 μm or less. Furthermore, the inventors confirmed that by melting the above glass raw material composition to produce molten glass, the delayed dissolution of silica sand and aluminum oxide can be reduced regardless of the proportion of the volume of pores with a diameter of 0.1 to 5 μm in the pore volume distribution of aluminum oxide contained in the glass raw material composition, measured by the mercury intrusion method for pores with a diameter of 0.004 to 5 μm, and thus conceived the present invention. The present invention has the following aspects.

[0012] In this invention, the components of the glass are represented by oxides such as SiO2 and Al2O3. Furthermore, in this invention, the content of each component relative to the total glass (glass composition) is expressed as a mole percentage based on the oxide.

[0013] [1] A method for producing 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 aforementioned silica sand has a D90 of over 600 μm. The aluminum oxide has a D90 of 200 μm or less, and this is a method for manufacturing molten glass.

[0014] [2] The method for producing molten glass according to [1], wherein the glass composition, on an oxide basis, contains 50 mol% or more of SiO2, 5 mol% or more of Al2O3, and 5 mol% or more of the total content of Li2O, Na2O, and K2O. [3] The method for producing molten glass according to [1], wherein the silica sand has a D90 of 700 μm or more. [4] The method for producing molten glass according to [1], wherein the silica sand has a D90 of 800 μm or more.

[0015] [5] The method for producing molten glass according to [1], wherein the silica sand has a D50 of 350 μm or more. [6] The method for producing molten glass according to [1], wherein the silica sand has a D50 of 400 μm or more. [7] The method for producing molten glass according to [1], wherein the silica sand has a D50 of 500 μm or more.

[0016] [8] The method for producing molten glass according to [1], wherein the molar ratio of silica sand to aluminum oxide in the glass raw material composition is 2.5 to 15 on an oxide basis. [9] The method for producing molten glass according to [1], wherein the glass raw material composition further contains at least one of boric acid and ZrO2.

[10] The method for producing molten glass according to [1], wherein the total content of SiO2, Al2O3, Li2O, Na2O, and K2O in the glass composition of the molten glass is 60 to 100 mol%.

[0017]

[11] The method for producing molten glass according to [1], wherein the molten glass has the following glass composition. Glass composition: On an oxide basis, the content of SiO2 is 50 to 75 mol%, the content of Al2O3 is 5 to 20 mol%, the content of B2O3 is 0 to 20 mol%, the total content of Li2O, Na2O, and K2O is 5 to 25 mol%, and the total content of MgO, CaO, SrO, and BaO is 0 to 20 mol%.

[0018]

[12] The method for producing molten glass according to [1], wherein the aluminum oxide has a ratio of the volume with a pore diameter of 0.1 to 5 μm of 0% or more and less than 60% in the pore volume distribution with a pore diameter range of 0.004 to 5 μm measured by the mercury intrusion method.

[0019]

[13] A method for producing a glass article using the method for producing molten glass according to any one of [1] to

[12] , comprising producing molten glass by the production method, shaping the obtained molten glass, and slowly cooling the shaped glass.

Advantages of the Invention

[0020] According to the method for producing molten glass of the present invention, since a glass raw material composition containing silica sand with a D90 exceeding 600 μm and aluminum oxide with a D90 of 200 μm or less is melted to produce molten glass having a specific glass composition, the slow melting of the glass raw material composition can be reduced. Since the method for producing a glass article of the present invention produces molten glass by the method for producing molten glass of the present invention, it is difficult for the homogeneity, bubble quality, and productivity to decrease due to the slow melting of the glass raw material composition, and high-quality glass articles can be efficiently produced.

Embodiments for Carrying Out the Invention

[0021] The measurement methods for the "particle size" and the "pore volume distribution of aluminum oxide by mercury intrusion porosimetry" in the present invention are as follows. <Measurement Method of Particle Size> "D50" is the average particle size represented by the 50% diameter in the cumulative fraction. The D50 of the glass raw material is the 50% diameter in the volume-based cumulative fraction obtained by measuring the particle size by the laser diffraction method. "D90" is the 90% diameter in the volume-based cumulative fraction obtained by measuring the particle size by the laser diffraction method.

[0022] <Measurement Method of Pore Volume Distribution of Aluminum Oxide by Mercury Intrusion Porosimetry> 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. Then, the horizontal axis is the pore diameter (unit: μm), and the vertical axis is dV / d(logD) (unit: cm 3 / g), and the pore volume distribution (Log differential pore volume distribution) is obtained.

[0023] In the pore volume distribution in the range of the obtained pore diameter of 0.004 to 5 μm, the ratio of the volume with a pore diameter of 0.1 to 5 μm is determined. Specifically, the ratio of the integrated value of the pore volume in the range of a pore diameter of 0.1 to 5 μm to the integrated value of the pore volume in the range of a pore diameter of 0.004 to 5 μm is determined and taken as the "ratio of the volume with a pore diameter of 0.1 to 5 μm".

[0024] [Measurement conditions for a fully automated pore size distribution analyzer] Sample amount: approximately 0.3-0.4g. Pre-treatment: Heat treatment in a dryer at 150°C for 1 hour. Mercury contact angle: 140deg. Mercury surface tension: 480dyn / cm.

[0025] <Method for manufacturing molten glass> The present invention relates to a method for producing molten glass, which involves melting a glass raw material composition containing a silicon source, an aluminum source, and an alkali metal source to produce molten glass having a specific glass composition. The silicon source is a compound that becomes SiO2 upon melting. The aluminum source is a compound that becomes Al2O3 upon melting. In this invention, the silicon source includes silica sand, and the aluminum source includes aluminum oxide.

[0026] [Silica sand] The silica sand in the glass raw material composition has a D90 of over 600 μm. By using silica sand with a D90 of over 600 μm, the delay in melting of the glass raw material composition during melting can be effectively reduced. A D90 of 700 μm or more is preferable, and 800 μm or more is more preferable. The upper limit of D90 is preferably 1200 μm or less, and more preferably 1100 μm or less, in order to reduce the delay in melting of the silica sand.

[0027] The silica sand in the glass raw material composition preferably has a D50 of 350 μm or more, more preferably 400 μm or more, and even more preferably 500 μm or more. By using silica sand with a D50 of 350 μm or more, the delay in melting of the glass raw material composition during melting can be further reduced. The upper limit of D50 is preferably 800 μm or less, and more preferably 700 μm or less, in order to further reduce the delay in melting of the silica sand during melting. In the present invention, one or more known silicon sources other than silica sand may be used, as long as they do not impair the effects of the present invention.

[0028] [Aluminum Oxide] The aluminum oxide in the glass raw material composition has a D90 of 200 μm or less. By using aluminum oxide with a D90 of 200 μm or less, the delay in melting of the glass raw material composition during melting can be effectively reduced. The D90 of the aluminum oxide is preferably 150 μm or less, more preferably 100 μm or less, even more preferably 90 μm or less, and particularly preferably 85 μm or less.

[0029] The lower limit of the D90 of aluminum oxide is preferably 10 μm or more, and more preferably 30 μm or more. This is because if the aluminum oxide is too fine, there is a possibility that it may scatter during the aluminum oxide transport process. In the present invention, one or more known aluminum sources other than aluminum oxide may be used, as long as they do not impair the effects of the present invention.

[0030] In the glass raw material composition, the proportion of the volume of pores with a diameter of 0.1 to 5 μm (hereinafter also simply referred to as "the proportion of the volume of pores with a diameter of 0.1 to 5 μm") in the pore volume distribution in the range of pore diameters of 0.004 to 5 μm, measured by the mercury intrusion method, is not specified. According to Patent Document 1, if the proportion of the volume of pores with a diameter of 0.1 to 5 μm is 60% or more, the delay in dissolution of aluminum oxide during melting can be effectively reduced. Furthermore, the proportion of the volume of pores with a diameter of 0.1 to 5 μm is more preferably 70% or more, and even more preferably 80% or more, as this can more effectively reduce the delay in dissolution of aluminum oxide during melting.

[0031] However, in the method for manufacturing molten glass of this embodiment, even if the proportion of the volume of pores with a diameter of 0.1 to 5 μm is less than 60%, the delay in the melting of aluminum oxide during melting can be suppressed. If the proportion of the volume of pores with a diameter of 0.1 to 5 μm is not a requirement, the range of aluminum oxides that can be used as raw materials for the glass raw material composition increases, and costs can be reduced. The proportion of the volume of pores with a diameter of 0.1 to 5 μm is more preferably 55% or less, and even more preferably 50% or less.

[0032] [Alkali metal source] In this invention, alkali metals refer to Na, K, and Li. The alkali metal source is a compound that becomes Na2O, K2O, and Li2O upon melting. Examples of alkali metal sources include alkali metal carbonates, sulfates, nitrates, oxides, hydroxides, chlorides, and fluorides. These may be used individually or in combination of two or more. Furthermore, the particle size is not particularly limited, and known alkali metal sources can be used. Examples of alkali metal carbonates include sodium carbonate, potassium carbonate, and lithium carbonate, and sodium carbonate (soda ash) is particularly suitable in terms of ease of handling.

[0033] [Alkaline earth metal source] The glass raw material composition may contain an alkaline earth metal source in addition to the components listed above. In this specification, alkaline earth metals refer to Mg, Ca, Ba, and Sr. The alkaline earth metal source is a compound that forms MgO, CaO, BaO, and SrO upon melting. Examples of alkaline earth metal sources include alkaline earth metal carbonates, sulfates, nitrates, oxides, hydroxides, chlorides, and fluorides. These may be used individually or in combination of two or more. Furthermore, the particle size is not particularly limited, and known alkaline earth metal sources can be used. Complex carbonates such as dolomite and complex oxides such as calcined dolomite can also be used.

[0034] [Boron source] The glass raw material composition may contain a boron source. Examples of boron sources include boric acid, boron oxide (B2O3), and colemanite. These may be used individually or in combination of two or more. Examples of boric acid include orthoboric acid (H3BO3), metaboric acid (HBO2), and tetraboric acid (H2B4O7).

[0035] [Other glass raw materials] The glass raw material composition may contain compounds other than those mentioned above that are known as glass raw materials, as long as they do not impair the effects of the present invention. Examples of these other compounds 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 individually or in combination of two or more.

[0036] [Glass raw material composition] A glass raw material composition is prepared by mixing glass raw materials such as silicon sources, aluminum sources, and alkali metal sources to achieve the target glass composition. The glass composition of the glass raw material composition is adjusted so that, in terms of oxides, it is approximately the same as the glass composition of the target molten glass, excluding components that are easily volatile 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. In addition, clarifying agents and oxides with clarifying properties may be mixed in as easily volatile components.

[0037] In the present invention, the glass composition (based on oxides) of the molten glass is preferably such that the SiO2 content is 50 mol% or more, the Al2O3 content is 5 mol% or more, and the total content of Li2O, Na2O, and K2O is 5 mol% or more. Therefore, the glass composition (based on oxides) of the molten glass is preferably such that the total of these elements is 60 to 100 mol%.

[0038] The ratio of silica sand to aluminum oxide in the glass raw material (molar ratio based on oxides) is preferably 2.5 or higher, and more preferably 4 or higher, in order to prevent undissolved aluminum oxide. Furthermore, it is preferably 15 or lower, and more preferably 12 or lower, in order to prevent undissolved silica sand. Furthermore, the glass raw material composition may further include, in addition to silica sand, aluminum oxide, and an alkali metal source, at least one of boric acid and ZrO2. Even with glass compositions containing boric acid or ZrO2, which have significantly different melting points from silica and alumina, such as alkali aluminosilicate glass, it is possible to prevent delayed melting of the raw materials and form a uniform molten glass.

[0039] The following compositions (1) to (4) are considered preferred glass compositions (total 100 mol%) for molten glass. Composition (1): 50-75 mol% SiO2, 5-20 mol% Al2O3, 0-20 mol% B2O3, 5-25 mol% total of Li2O, Na2O, and K2O, and 0-20 mol% total of MgO, CaO, SrO, and BaO. Composition (2): 50-75 mol% SiO2, 5-20 mol% Al2O3, 5-25 mol% total of Li2O, Na2O, and K2O, 0-20 mol% total of MgO, CaO, SrO, and BaO, 0-5 mol% total of ZrO2 and TiO2, 0-5 mol% of Fe2O3, and 0-5 mol% of Co3O4. Composition (3): 50-75 mol% SiO2, 5-20 mol% Al2O3, 5-25 mol% total of Li2O, Na2O, and K2O, 1-20 mol% B2O3, and 0-25 mol% total of MgO, CaO, SrO, and BaO. Composition (4): 50-75 mol% SiO2, 5-20 mol% Al2O3, 5-25 mol% total of Li2O, Na2O, and K2O, 1-15 mol% B2O3, 0-15 mol% total of MgO, CaO, SrO, and BaO, 0-5 mol% total of ZrO2 and TiO2, 0-5 mol% Fe2O3, and 0-5 mol% Co3O4.

[0040] Furthermore, in alkali aluminosilicate glass containing at least one of boric acid and ZrO2, the B2O3 content is preferably 0 to 6 mol%, more preferably 6 to 10 mol%. The ZrO2 content is preferably 0 to 2 mol%, more preferably 2 to 5 mol%. A preferred composition when boric acid and optionally ZrO2 are included is the following composition (5). Composition (5): SiO2 is 50-75 mol%, Al2O3 is 5-20 mol%, the total of Li2O, Na2O, and K2O is 1-15 mol%, B2O3 is 1-15 mol%, and the total of MgO, CaO, SrO, and BaO is 0-15 mol%, the total of ZrO2 and TiO2 is 0-5 mol%, the content of Fe2O3 is 0-5 mol%, and the content of Co3O4 is 0-5 mol%.

[0041] [Melting process] In the method for producing molten glass of the present invention, the above-mentioned glass raw material composition is melted. The melting step in which the glass raw material composition is melted can be carried out by known methods. Preferably, the glass raw material composition is melted by placing it in a melting furnace. In the method of melting a glass raw material composition by introducing it into a melting furnace, a layer of suspended matter forms on the surface of the molten glass liquid in the furnace due to the delayed melting of the glass raw material composition. This layer blocks heat from above the liquid surface, leading to insufficient heating and uneven heating. Therefore, applying the present invention to improve the meltability of the glass raw material composition has a significant effect.

[0042] The melting furnace is not particularly limited and may be a batch type or a continuous type. For example, the glass raw material composition and, if necessary, cullet having the same glass composition as the target molten glass are continuously fed into the melting furnace and heated to about 1500°C to 1700°C to melt and produce molten glass. Cullet is glass waste discharged during the glass manufacturing process.

[0043] <Method of manufacturing glass articles> In the method for manufacturing glass articles of the present invention, molten glass is manufactured using the method for manufacturing molten glass of the present invention. The molten glass obtained in the melting process described above is molded into the desired shape in the molding process. If the glass article is in the form of a sheet, the molding process can be carried out using known methods such as the float method, down-draw method, or fusion method to form the desired shape. Next, the molded glass is slowly cooled in a slow-cooling process as needed. After that, post-processing is carried out in a post-processing process as needed using known methods such as cutting and / or polishing. This yields the glass article.

[0044] <Mechanism of Action> According to the present invention, in a glass raw material composition containing silica sand, aluminum oxide, and an alkali metal source, by using silica sand with a D90 of more than 600 μm and aluminum oxide with a D90 of 200 μm or less, the delay in the melting of the silica sand and aluminum oxide during the melting process of the glass raw material composition can be reduced.

[0045] The reason is not clear, but it can be inferred as follows: In the method for producing molten glass of the present invention, when the glass raw material composition is heated, silica sand and an alkali metal source react to produce a low-melting-point reactant (xSiO2-yA2O (A represents an alkali metal, and x and y represent the reaction ratio)). The silica sand contained in the glass raw material composition has a D90 of over 600 μm and contains large particles. Therefore, the reaction between the silica sand and the alkali metal source is moderately suppressed. As a result, the reactant has a low proportion of SiO2 (x / y) and is highly reactive with aluminum oxide. Moreover, the aluminum oxide has a D90 of 200 μm or less and contains few large particles that are difficult to dissolve. From these points, aluminum oxide dissolves well in the reactant and is less likely to be delayed in dissolving. Also, silica sand dissolves more easily than aluminum oxide. From these points, it is presumed that the delay in dissolving of silica sand and aluminum oxide during the melting process of the glass raw material composition is reduced. [Examples]

[0046] The present invention will be described in more detail below using examples. The present invention is not limited to these examples. <Measurement of particle size> Using a laser diffraction / scattering particle size distribution analyzer (Horiba, Ltd., product name: LA-950), the particle size distribution was measured by wet laser diffraction, and D10, D50, or D90 was determined. If particles were aggregated in the dispersion medium, the aggregates were dispersed by ultrasound, and the particle size distribution of the primary particles constituting the aggregates was measured.

[0047] <Method for measuring the temperature at the bottom of the crucible (evaluation of the melting delay of glass raw material compositions)> A glass raw material composition was prepared by combining silica sand, aluminum oxide, an alkali metal source, and other raw materials to obtain an alkali aluminosilicate monoglass with a predetermined glass composition. The prepared glass raw material composition and cullet were mixed in a predetermined ratio and placed in a crucible, where they were melted. The temperature at the bottom of the crucible was measured during glass melting, and the degree of delay in melting of silica sand or aluminum oxide was compared.

[0048] An alumina crucible (product name: SSA-S, manufactured by Nikkatoh, inner diameter 240 mm, height 245 mm) was used as the crucible. As the melting furnace, a large electric furnace with two chambers equipped with a movable crucible holder and heaters installed at the top of each furnace chamber was used to reproduce the heating conditions of the upper combustion space where the molten glass is heated from above in a continuous melting furnace. The sides and bottom of the alumina crucible were covered with insulating boards at least 20 cm thick to block heat input from the sides and bottom to the glass raw material composition inside the crucible.

[0049] To replicate the temperature history of a glass melting furnace in actual production, the first furnace chamber was heated at 1350°C for 30 minutes (dew point 50°C), and immediately afterward, the second furnace chamber was heated at 1550°C for 120 minutes (dew point 50°C).

[0050] To evaluate the degree of delayed melting of the glass raw material, the crucible bottom temperature was measured using the following procedure. First, the glass raw material composition and cullet were mixed at room temperature in a predetermined ratio and placed in a crucible. The total amount of glass raw material composition and cullet was 2 kg in terms of glass mass. Next, the crucible was placed in the first furnace chamber and heated under the above conditions, then transferred to the second furnace chamber and heated under the above conditions, and finally removed 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 highest temperature was recorded as the crucible bottom temperature.

[0051] The higher the crucible bottom temperature, the less the melting delay of the glass raw material composition inside the crucible is reduced, and the thinner the floating material layer becomes. Therefore, a higher crucible bottom temperature indicates less heat insulation by the floating material layer on the molten glass surface, and that the temperature of the molten glass was raised more efficiently by the heat from the heater.

[0052] <Glass raw materials> The following glass materials are used. Silica sand: Silica sand A or silica sand B shown below was used. Silica sand A: D90=946μm, D50=559μm Silica sand B: D90=470μm, D50=262μm

[0053] Aluminum oxide: The following alumina S and T were used. Alumina S:D90 = 140 μm, Percentage of volume with pore size 0.1-5 μm = 56% Alumina T:D90 = 82 μm, Percentage of volume with pore size 0.1-5 μm = 96% Alkali metal source: Soda ash (1) (D50 = 400 μm). Magnesium source: Magnesium oxide (1) (D50 = 10 μm). Other ingredients: Sodium sulfate (clarifying agent).

[0054] [Examples 1-4] Examples 1 and 2 are examples of actual cases, and Examples 3 and 4 are comparative examples. The silica sand and aluminum oxide shown in Table 1, the alkali metal source and magnesium source mentioned above, and the clarifying agent were prepared to obtain the following glass composition (i) to create a glass raw material composition. The amount of clarifying agent added was 1.4 mol% relative to the glass raw material composition. The crucible bottom temperature was measured for each example of glass raw material composition using the method described above. The mass ratio of glass raw material composition to cullet was set to 50:50. The results are shown in Table 1.

[0055] <Glass composition (i)> SiO2: 68.0 mol%, Al2O3: 10.0 mol%, MgO: 8.0 mol%, Na2O: 14.0 mol%. The molar ratio of SiO2 to Al2O3 is 6.8.

[0056] [Table 1]

[0057] As shown in Table 1, Examples 1 and 2, which used silica sand A with a D90 of over 600 μm and alumina S and T with a D90 of 200 μm or less, had higher crucible bottom temperatures compared to Examples 3 and 4, which used silica sand B with a D90 of less than 600 μm. Therefore, in Examples 1 and 2, the suspended solids layer thickness was thinner compared to Examples 3 and 4, and the delay in melting the glass raw material composition in the crucible was reduced.

[0058] Furthermore, as shown in Table 1, Example 2, in which alumina T was used as aluminum oxide, had a higher crucible bottom temperature compared to Example 1, in which alumina S was used. This is presumed to be because the D90 of alumina T is smaller than that of alumina S, and the proportion of the volume of pores with a diameter of 0.1 to 5 μm in alumina T is higher than that of alumina S, thus more effectively reducing the delay in the melting of aluminum oxide during melting.

Claims

1. A glass raw material composition containing silica sand, aluminum oxide, and an alkali metal source is melted, and SiO ２ and Al ２ O ３ A method for producing molten glass having a glass composition including, The aforementioned silica sand has a D90 of over 600 μm. A method for producing molten glass, wherein the aluminum oxide has a D90 of 200 μm or less.

2. The glass composition has, on an oxide basis, a content of SiO ２ of 50 mol% or more, a content of Al ２ O ３ of 5 mol% or more, and a total content of Li ２ O, Na ２ O, K ２ O of 5 mol% or more. The method for producing the molten glass according to claim 1.

3. The method for producing molten glass according to claim 1, wherein the silica sand has a D90 of 700 μm or more.

4. The method for producing molten glass according to claim 1, wherein the silica sand has a D90 of 800 μm or more.

5. The method for producing molten glass according to claim 1, wherein the silica sand has a D50 of 350 μm or more.

6. The method for producing molten glass according to claim 1, wherein the silica sand has a D50 of 400 μm or more.

7. The method for producing molten glass according to claim 1, wherein the silica sand has a D50 of 500 μm or more.

8. The method for producing molten glass according to claim 1, wherein the molar ratio of silica sand / aluminum oxide on an oxide basis in the glass raw material composition is 2.5 to 15.

9. The glass raw material composition is boric acid and ZrO ２ A method for producing molten glass according to claim 1, further comprising at least one of the following.

10. In the glass composition of the molten glass, SiO ２ and Al ２ O ３ and Li ２ O and Na ２ O and K ２ A method for producing molten glass according to claim 1, wherein the total content of O is 60 to 100 mol%.

11. The method for producing molten glass according to claim 1, wherein the molten glass has the following glass composition. Glass composition: Based on oxides, SiO ２ The content is 50-75 mol%, Al ２ O ３ The content is 5-20 mol%, B ２ O ３ The content is 0 to 20 mol%, Li ２ O, Na ２ O, K ２ The total content of O is 5 to 25 mol%, and the total content of MgO, CaO, SrO, and BaO is 0 to 20 mol%.

12. The method for producing molten glass according to claim 1, wherein the aluminum oxide has a pore volume distribution in the range of pore diameters from 0.004 to 5 μm, measured by the mercury intrusion method, in which the proportion of the volume of pores with a diameter of 0.1 to 5 μm is 0% or more and less than 60%.

13. A method for manufacturing a glass article using a method for manufacturing molten glass according to any one of claims 1 to 12, A method for manufacturing glass articles, comprising: producing molten glass by the above manufacturing method; molding the obtained molten glass; and slowly cooling the molded glass.

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