Production method for molten glass, production method for glass, and device for producing molten glass

Abstract

Provided is a production method for molten glass by which molten glass to be supplied to a succeeding forming step is obtained from raw materials for glass, the production method including supplying a non-oxidizing gas to an upper space of a tank in which the contents including molten glass are accommodated, in a direction toward the surface of the contents.

Description

Molten glass manufacturing method, glass manufacturing method, and molten glass manufacturing apparatus

[0001] This application claims priority to Japanese Patent Application No. 2024-124556, filed on July 31, 2024, the contents of which are incorporated herein by reference.

[0002] The manufacturing process of glass articles such as glass sheets includes a molten glass manufacturing process and a forming process. The molten glass manufacturing process is a process for manufacturing molten glass from glass raw materials to be used in the forming process. The molten glass manufacturing process includes a melting process for melting the glass raw materials, and may further include processing steps such as fining and homogenization for improving the quality of the molten glass.

[0003] In a molten glass manufacturing process, a vessel is used to store an object containing molten glass. To prevent damage to the vessel caused by high-temperature molten glass, a highly durable material such as a refractory material or a precious metal is usually used as a constituent material of the vessel. It is also known to use platinum on the inner surface of the vessel to improve the heat resistance and corrosion resistance of the melting vessel in the melting process (for example, Patent Document 1).

[0004] Japanese Patent Application Publication No. 2010-202444 (A)

[0005] In recent years, requirements for the quality of glass articles have become increasingly stringent. In particular, it has been pointed out that foreign matter originating from the constituent materials of the vessel mixed into the glass article affects the quality of the glass article, and it is therefore necessary to avoid the inclusion of such foreign matter as much as possible. It is known that such foreign matter is formed when the constituent materials of the vessel, particularly platinum, are oxidized by the atmosphere in the head space, volatilized as oxides, and then solidified.

[0006] In order to reduce the contamination of such foreign matter, the supply of a non-oxidizing gas to the upper space of the vat has also been considered. Although supplying a non-oxidizing gas can suppress the generation of oxides from the vat's constituent materials to some extent, it has not always been possible to sufficiently reduce the amount of foreign matter in the glass articles. This is thought to be because the oxides tend to solidify on the inner surface of the vat, causing foreign matter to adhere and accumulate on the inner surface of the vat. This foreign matter is then detached from the inner surface of the vat by the flow of the supply gas and falls onto the contents inside the vat.

[0007] One aspect of the present disclosure provides a technology that can suppress the inclusion of foreign matter originating from the constituent material of a tank in a glass article.

[0008] One aspect of the present disclosure is a method for producing molten glass, in which molten glass to be subjected to a subsequent forming step is obtained from glass raw materials, the method comprising supplying a non-oxidizing gas to an upper space of a tank containing contents including at least one of glass raw materials and molten glass in a supply direction toward a surface of the contents.

[0009] According to one aspect of the present disclosure, a technology is provided that can suppress the inclusion of foreign matter originating from the constituent material of the tank in a glass article.

[0010] FIG. 6 is a flow diagram of a method for manufacturing a glass article according to one embodiment. FIG. 7 is a vertical cross-sectional view of a molten glass manufacturing apparatus according to one embodiment. FIG. 8 shows a cross-sectional view along line II of FIG. 2. FIG. 9 is a cross-sectional view of a molten glass manufacturing apparatus equipped with a gas supply unit according to a modified example. FIG. 10 is a cross-sectional view of a molten glass manufacturing apparatus equipped with a gas supply unit according to another modified example. FIG. 11 is a cross-sectional view of a molten glass manufacturing apparatus equipped with a gas supply unit according to yet another modified example. FIG. 12 is a cross-sectional view of a molten glass manufacturing apparatus used in the examples.

[0011] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. Note that the same or corresponding components in each drawing are denoted by the same reference numerals, and descriptions thereof may be omitted. In each drawing, the x-axis direction, y-axis direction, and z-axis direction are mutually orthogonal directions. The x-axis direction and y-axis direction are two directions contained in a horizontal plane, and the z-axis direction may be a vertical direction. The z-axis direction may also be referred to as the up-down direction.

[0012] First, a molten glass manufacturing method and basic steps of the glass manufacturing method will be described. Fig. 1 shows a flow diagram of a glass manufacturing method according to one embodiment. As shown in Fig. 1, the glass manufacturing method may include a molten glass manufacturing step (S10), a forming step (S20), an annealing step (S30), and optionally a processing step (S40).

[0013] The molten glass manufacturing step (S10) is a step of manufacturing molten glass from glass frits to be subjected to the subsequent forming step (S20). That is, after the molten glass manufacturing step (S10), the process can proceed to the forming step (S20) without going through any other steps. The molten glass manufacturing step (S10) includes a melting step (S11) of melting glass frits, and may further include a treatment step for improving the quality of the molten glass. The treatment step may include at least one of a fining step (S12) and a homogenization step (S13).

[0014] The melting step (S11) is a step of melting glass frits. In the melting step (S11), the glass frits are charged into a tank and heated to a temperature according to the type of glass frit by a heat source such as a heater, a burner, or an electrode for electrical heating arranged inside and / or outside the tank, to obtain molten glass.

[0015] The fining step (S12) is a step of fining the molten glass obtained in the melting step, and may include removing bubbles contained in the molten glass. Methods for removing bubbles include reducing the pressure of the atmosphere surrounding the molten glass and heating the molten glass to a higher temperature. A fining agent may also be used for the fining step (S12). The homogenization step (S13) is a step of improving the chemical or thermal homogeneity of the molten glass refined in the fining step (S12), and may include stirring the molten glass.

[0016] The forming step (S20) may be a step of forming the molten glass produced in the molten glass production step (S10) into a glass article of a desired shape, for example, a plate glass. When the glass article is a plate glass, the forming step (S20) may be performed by a float method, a fusion method, a roll-out method, a down-draw method, a Colburn method, or the like. The annealing step (S30) may be a step of annealing the glass article while transporting it using a transport roller, or the like. Furthermore, the processing step (S40) may be a step of performing processing such as cutting, grinding, polishing, and coating on the formed and annealed glass article.

[0017] The glass article manufactured by the glass manufacturing method according to one embodiment may be a glass plate. Applications of such glass plates include glass for display devices (such as display cover glass), glass parts for semiconductor devices and other electronic components (such as lenses and substrates), window glass for vehicles, and window glass for buildings. The type of glass used in the manufactured glass article may be, for example, alkali-free glass, aluminosilicate glass, borosilicate glass, soda-lime glass, or the like. The alkali-free glass is a glass containing Na ２ O.K. ２ The glass is substantially free of alkali metal oxides such as O.

[0018] In the molten glass manufacturing step (S10), a molten glass manufacturing apparatus (described in detail later) including a tank for accommodating contents including molten glass is used. Furthermore, in all of the above-mentioned melting step (S11), fining step (S12), and homogenizing step (S13), a tank for accommodating contents including molten glass is used. When the molten glass manufacturing step (S10) includes the melting step (S11), fining step (S12), and homogenizing step (S13), a different tank may be used for each step. In this case, after completion of one step, the molten glass is sent to another tank for use in the next step. The same tank may also be used for two or more steps included in the molten glass manufacturing step (S10). Furthermore, all steps included in the molten glass manufacturing step (S10) may be performed in the same tank. That is, one and the same tank may be used throughout the melting step (S11), fining step (S12), and homogenizing step (S13).

[0019] 2 and 3 show a molten glass manufacturing apparatus 1 used in a molten glass manufacturing method according to one embodiment. An example of the molten glass manufacturing apparatus 1 used in the melting step (S11) is shown in Fig. 2 and 3. The molten glass manufacturing apparatus 1 may be one that performs continuous processing or batch processing.

[0020] Fig. 2 is a cross-sectional view of the molten glass manufacturing apparatus 1 taken along a center line CL extending along the z direction (vertical direction) of the melting furnace 10 or the tank 12 included in the melting furnace 10, and Fig. 3 is a cross-sectional view taken along line I-I in Fig. 2. The molten glass manufacturing apparatus 1 shown in Figs. 2 and 3 is an apparatus including a melting furnace 10 used in the melting step (S11). Figs. 2 and 3 show an example in which the melting furnace 10 has a cylindrical shape as a whole, but in the present disclosure, the shape of the furnace is not limited to that shown in the drawings and may have a rectangular parallelepiped shape, a cubic shape, a prismatic shape, or the like.

[0021] The melting furnace 10 includes a vessel 12 that contains at least molten glass. The vessel 12 includes a sidewall 12S that surrounds the sides of the contents and a bottom 12B below the sidewall 12S. The melting furnace 10 also includes a ceiling 11 that covers the entire upper portion of the vessel 12. The sidewall 12S, the bottom 12B, and the ceiling 11 may be made of a refractory material such as electroformed bricks. In the example shown in FIG. 2 , the inner surface of the lower portion of the vessel 12 is made of a precious metal, preferably a platinum, surface. Such a precious metal surface can be formed by lining the vessel with a plate-shaped member containing a precious metal or a precious metal alloy, preferably a plate-shaped member containing platinum or a platinum alloy. In other words, the vessel 12 includes a precious metal vessel 15, preferably a platinum vessel, and the contents containing molten glass are contained in this precious metal vessel 15. By storing the contents including the molten glass G2 in a precious metal tank 15 such as a platinum tank, the heat resistance and corrosion resistance of the tank are improved, and damage caused by the high-temperature molten glass G2 can be reduced.

[0022] The frit G1 is charged into the tank 12 through an inlet (not shown). The frit G1 is prepared by mixing a plurality of materials, and its composition is determined according to the composition of the desired glass article to be manufactured. The frit G1 may be a powdered raw material or a granulated raw material obtained by granulating the powdered raw material. The frit G1 may contain glass cullet obtained from discarded glass. The frit G1 may also contain a fining agent.

[0023] When the molten glass manufacturing apparatus 1 is a continuous apparatus, frit G1 is continuously introduced, and the frit G1 forms a layer (also referred to as a cold top or a raw material batch) on the liquid surface of the molten glass G2, and the frit G1 is melted. In this case, as shown in FIG. 2 , the frit G1 and the molten glass G2 are contained in a vessel 12, and the surface SF of the contents of the vessel 12 is the surface of the frit G1. The maximum temperature of the surface of the frit G1 layer may preferably be 1000°C or less, more preferably 500°C or less. The temperature of the molten glass G2 is 1200°C or more and 1600°C or less. Note that, although FIGS. 2 and 3 show an example in which a cold top is formed, the embodiment according to the present disclosure may be a cold top type or a hot top type.

[0024] The glass frit G1 gradually melts due to the heat transferred from the molten glass G2. The molten glass G2 gradually moves downward and can be taken out from an outlet (not shown) provided in the lower part of the tank 12.

[0025] In the conventional molten glass production process (S10), foreign matter originating from the constituent materials of the vat 12 is mixed into the molten glass, which can degrade the quality of the resulting glass product. The mixing of such foreign matter is thought to occur as follows: The constituent materials of the vat 12 volatilize as oxides from the inner surface of the vat 12 exposed to the upper space UP of the heated vat 12 and are released into the upper space. The oxides then solidify and become foreign matter in a relatively low-temperature area of ​​the inner surface of the vat 12, for example, in a location near the relatively low-temperature glass frit G1, and adhere to and accumulate on the inner surface of the vat 12. When subjected to some kind of stimulus, such foreign matter can detach from the inner surface of the vat 12 and be mixed into the glass frit G1 or the molten glass G2.

[0026] To prevent such contamination by foreign matter, the molten glass manufacturing apparatus 1 according to this embodiment includes a gas supply unit 20 that supplies a non-oxidizing gas to the upper space UP. The gas supply unit 20 may be connected to a gas tank (not shown) that contains compressed non-oxidizing gas and is installed outside the vessel 12, thereby allowing the non-oxidizing gas to be sent or blown into the upper space UP of the vessel 12 at a desired flow rate. The non-oxidizing gas reduces the oxygen concentration in the atmosphere in the upper space UP, making the upper space UP a non-oxidizing atmosphere, thereby preventing the generation of oxides from the constituent materials of the vessel 12. When the inner surface of the precious metal vessel 15 is exposed to the upper space UP, the generation of oxides, such as platinum oxide, from the precious metal vessel 15 can be prevented.

[0027] Examples of non-oxidizing gases include inert gases such as nitrogen gas, hydrogen gas, carbon dioxide, and argon gas. Of these, nitrogen gas is preferred because it is highly safe and inexpensive. The above gases can be used alone or in combination of two or more.

[0028] The oxygen concentration in the upper space UP can be adjusted to preferably 5% by volume or less, more preferably 3% by volume or less, and further preferably 1% by volume or less. The oxygen concentration can be controlled by adjusting the flow rate of the supplied non-oxidizing gas, etc., depending on the size of the vessel 12, particularly the volume of the upper space UP, the flow rate of air introduced together with the glass raw materials, etc.

[0029] Furthermore, in this embodiment, the non-oxidizing gas is supplied from the gas supply unit 20 to the upper space UP in a supply direction Ds toward the surface SF of the contents. This makes it easier for the non-oxidizing gas supplied from the gas supply unit 20 to hit the surface SF of the contents in the vessel 12 and less likely to hit the inner surface of the side wall 12S of the vessel 12. This prevents foreign matter adhering to the inner surface of the vessel 12 from being detached from the inner surface by the force of the gas flow and falling onto the contents in the vessel 12. When the inner surface of the precious metal vessel 15 is exposed to the upper space UP, foreign matter derived from the precious metal adhering to the inner surface of the precious metal vessel 15, such as platinum oxide, can be prevented from being detached from the inner surface and falling onto the contents. This prevents foreign matter from being mixed into the molten glass produced by the molten glass producing apparatus 1, and ultimately prevents foreign matter from being mixed into the resulting glass article.

[0030] Here, the supply direction Ds toward the surface SF of the contained material means, more specifically, that an imaginary line Ls drawn along the supply direction Ds intersects with the surface SF of the contained material, as shown in FIG. 2 . The supply direction Ds may be a direction passing through the center line of a supply hole 21, which is a hole formed in the gas outlet portion of the gas supply unit 20. An extension of the center line of the supply hole 21 may coincide with the imaginary line Ls. When the gas supply unit 20 is a supply pipe as shown in FIG. 2 , the gas supply hole 21 is formed at the tip of the end of the supply pipe, and the end face at the tip is formed in a direction perpendicular to the axial direction of the supply pipe, the direction of the extension of the center line of the supply pipe can be defined as the supply direction Ds. Furthermore, as long as the gas flow discharged from the gas supply unit 20 can be visualized, the direction of the extension of the direction of the center of the gas flow near the gas supply hole 21 may be defined as the supply direction Ds.

[0031] Furthermore, it is preferable that an imaginary line Ls drawn along the supply direction Ds intersects with the surface SF of the contents but does not intersect with the inner surface of the tank 12.

[0032] In the example shown in Fig. 2, the supply direction Ds of the non-oxidizing gas from the gas supply unit 20 is along the vertical direction (z direction). When the supply direction Ds is along the vertical direction, the flow of the non-oxidizing gas can be more reliably directed toward the surface SF of the contents, regardless of the shape, size, amount of contents, etc. of the tank 12, and this is preferable because it can more reliably prevent the non-oxidizing gas from hitting the exposed inner surface of the tank 12. However, the supply direction Ds may be angled with respect to the vertical direction (described below with reference to Fig. 4).

[0033] 2, the non-oxidizing gas is supplied from a gas supply unit 20 provided in the ceiling portion 11, but the gas supply unit may also be provided in the side wall 12S as long as the gas supply direction Ds is directed toward the surface SF of the contained items (described later with reference to FIG. 5). However, when the gas supply unit 20 is provided in the ceiling portion 11, the supply direction Ds is necessarily directed downward, which is preferable compared to when the gas supply unit 20 is provided in the side wall 12S, as it is easier to adjust the supply direction Ds so that the flow of the non-oxidizing gas is directed toward the surface SF of the contained items.

[0034] When the gas supply unit 20 is provided in the ceiling portion 11, the position of the gas supply unit 20 in the ceiling portion 11 is not particularly limited. However, it is preferable that the supply holes 21 of the gas supply unit 20 be located as close as possible to the center of the vessel 12 or the upper space UP, i.e., that they overlap with or are as close as possible to the center line CL of the vessel 12. The center line CL of the vessel 12 is also the center line of the upper space UP. Furthermore, as shown in FIG. 3, for example, when viewing the upper space UP in a cross section cut along a plane including the x and y directions (x-y plane) at the position of the supply holes 21, it is preferable that the supply holes 21 be located as close as possible to the center of the cross-sectional shape, i.e., that they overlap with or are as close as possible to the centroid of the cross-sectional shape of the upper space UP. For example, the gas supply unit 20 may be located at a position that overlaps the area from the centroid of the cross-sectional shape of the upper space UP to a position half the distance from the centroid to the inner surface of the sidewall 12S (the circular area Ar surrounded by a dotted line in the example of FIG. 3 ) when viewed in a cross section cut at the supply hole 21 of the gas supply unit. Furthermore, it is preferable that the supply hole 21 overlaps the center line CL of the vessel 12, and more preferably, the center line of the supply hole 21 coincides with the centroid of the cross-sectional shape of the upper space UP. By positioning the gas supply unit 20 so that the supply hole 21 overlaps the center line CL of the vessel 12 or is located as close as possible to the center line CL, variation in the distance from the supply hole 21 of the gas supply unit 20 to the sidewall 12S can be reduced. This allows for more uniform filling of the non-oxidizing gas in the upper space UP as a whole, and more uniform suppression of oxide generation throughout the upper space UP. Such an arrangement of the gas supply unit 20 in the ceiling portion 11 is particularly preferable when there is only one gas supply unit 20.

[0035] The supply amount F1 of the non-oxidizing gas supplied in the supply direction Ds toward the surface SF of the contents depends on the scale of the melting furnace 10, the volume of the tank, and the volume of the contents, and may be preferably 50% to 125%, more preferably 75% to 125%, as a ratio of the volume of the non-oxidizing gas supplied per minute to the volume of the upper space UP. Thus, in this specification, the supply amount of the non-oxidizing gas is defined as the ratio of the volume of the non-oxidizing gas supplied per minute to the volume of the upper space UP.

[0036] In the case of continuous operation in which glass frit G1 is continuously introduced, if the supply amount F1 defined above is 50% or more, the oxygen concentration in the upper space UP can be maintained low even if air is continuously introduced together with the glass frit G1. On the other hand, if the supply amount F1 is 125% or less, the energy of the gas flow colliding with the surface SF of the contents increases, causing the glass frit G1 constituting the upper layer to scatter and hinder the melting process. ２ In addition, when there are a plurality of gas supply units 20 that supply non-oxidizing gas in the supply direction Ds toward the surface SF of the contained items, the supply amount of non-oxidizing gas supplied in the supply direction Ds toward the surface SF of the contained items is the sum of the supply amounts of gas from each gas supply unit 20.

[0037] In this embodiment, the non-oxidizing gas is supplied in a supply direction Ds toward the surface SF of the contained items. Alternatively, the non-oxidizing gas may be supplied in a supply direction not toward the surface SF of the contained items, e.g., horizontally, from a gas supply unit other than the gas supply unit shown in Figures 2 and 3. Even in such a case, the ratio (F1 / Ft x 100) of the supply amount F1 of the non-oxidizing gas supplied in the supply direction Ds toward the surface SF of the contained items to the total supply amount Ft of the non-oxidizing gas supplied to the upper space UP may be preferably 40% or more, more preferably 70% or more, and even more preferably 85% or more. This ensures that the proportion of the gas that strikes the surface SF of the contained items is sufficiently high and the proportion of the gas that strikes the inner surface of the side wall 12S of the vessel 12 is sufficiently reduced, thereby preventing foreign matter adhering to the inner surface of the vessel 12 from falling off and suppressing the incorporation of foreign matter into the molten glass G2. The above ratio (F1 / Ft x 100) is equal to the ratio (f1 / ft x 100) of the flow rate f1 of the non-oxidizing gas supplied in the supply direction Ds toward the surface SF of the contents to the total flow rate ft of the non-oxidizing gas supplied to the upper space UP.

[0038] From the viewpoint of preventing the gas flow from hitting (blowing) foreign matter adhering to the inner surface of the vessel 12, it is preferable that the ratio (F1 / Ft × 100) be substantially 100%, i.e., that all of the non-oxidizing gas be supplied in the supply direction Ds toward the surface SF of the contents. However, depending on the circumstances, it may be unavoidable to supply the gas in a direction not toward the surface SF of the contents. For example, an existing molten glass manufacturing apparatus may be equipped with an existing supply unit that supplies gas in a direction not toward the surface SF of the contents, e.g., horizontally, and an additional gas supply unit that supplies non-oxidizing gas in the supply direction Ds toward the surface SF of the contents may be installed in the molten glass manufacturing apparatus. In this case, it is necessary to supply gas at a certain flow rate from the existing supply unit as well to prevent deterioration. In such a case, the ratio (F1 / Ft × 100) may be 95% or less, or 90% or less.

[0039] The total supply amount Ft of the non-oxidizing gas supplied to the upper space UP may be preferably 100% to 200%, more preferably 150% to 200%, as a ratio of the volume of the non-oxidizing gas supplied per minute to the volume of the upper space UP. By making the total supply amount of the non-oxidizing gas 100% or more of the volume of the upper space UP, the oxygen concentration in the atmosphere of the upper space UP can be sufficiently suppressed even when the glass frit G1 is continuously added to the vessel 12. Furthermore, by making the total supply amount of the non-oxidizing gas 200% or less of the volume of the upper space UP, the energy of the gas flow colliding with the surface SF of the contents increases, which causes the glass frit G1 constituting the upper layer to scatter and interfere with the melting process, and the supplied N ２ This prevents the molten glass G2 from being cooled and interfering with the melting process.

[0040] The number of gas supply units 20 that supply non-oxidizing gas in the supply direction Ds toward the surface SF of the contained contents may be one as shown in Fig. 2, or may be multiple. The arrangement of the multiple gas supply units 20 is determined appropriately depending on the shape and size of the tank 12, the arrangement of other components included in the molten glass manufacturing apparatus 1, and the like, as long as each gas supply unit 20 can supply non-oxidizing gas in the supply direction Ds toward the surface SF of the contained contents and can prevent foreign matter from being mixed into the molten glass G2. The inner diameter of the gas supply hole 21 of one gas supply unit 20 may be 5 mm or more and 20 mm or less.

[0041] Fig. 4 shows a molten glass manufacturing apparatus 1 equipped with a gas supply unit 20 according to a modified example. In the example shown in Fig. 4, similar to the example shown in Fig. 2, the gas supply unit 20 is provided in the ceiling portion 11, and the supply direction Ds of the non-oxidizing gas is a direction toward the surface SF of the contents. However, in the gas supply unit 20 shown in Fig. 4, the supply direction Ds of the non-oxidizing gas forms an angle with respect to the vertical direction.

[0042] As described above, as long as the supply direction Ds of the non-oxidizing gas is directed toward the surface SF of the contents, i.e., as long as the imaginary line Ls drawn along the supply direction Ds intersects with the surface SF of the contents, the supply direction Ds does not necessarily have to be directed along the vertical direction. In the molten glass manufacturing apparatus 1, some additional components, such as a burner, measuring equipment, etc., may be provided on the ceiling 11 of the melting furnace 10, and the presence of such components may make it impossible to provide the gas supply unit 20 with the supply direction Ds directed along the vertical direction. Even in such a case, as long as the supply direction Ds is directed toward the surface SF of the contents, it is possible to suppress the intrusion of foreign matter into the molten glass G2 and to design the supply direction Ds to be inclined.

[0043] When the supply direction Ds of the non-oxidizing gas from the gas supply unit 20 is inclined with respect to the vertical direction, the angle α that the supply direction Ds makes with respect to the vertical direction may be preferably 30° or less, more preferably 15° or less. If the angle α is within the above range, it becomes easy to adjust the configuration of the gas supply unit 20 so that the supply direction Ds is directed toward the surface SF of the contained contents, and it can be adapted to different amounts of the contained contents and different sizes and shapes of the tank 12.

[0044] Furthermore, if the distance in the z direction from the gas supply hole 21 (more specifically, from the position of the center line at the tip of the gas supply hole 21) to the surface SF of the contents is H, and the distance along the x-y plane from the gas supply hole 21 (more specifically, from the position of the center line at the tip of the gas supply hole 21) to the inner surface of the side wall 12S is W, then tan α≦0.5W / H may be satisfied. When the cross section of the upper space UP along the x-y plane is circular and the gas supply hole 21 is located on the center line CL of the vessel 12, as shown in FIG. 3 , the distance W along the x-y plane from the gas supply hole 21 to the inner surface of the side wall 12S corresponds to the diameter of the circle. When the cross section of the upper space UP along the x-y plane is not circular, the distance W may be a minimum value.

[0045] Figure 5 shows a molten glass manufacturing apparatus 1 equipped with a gas supply unit 20 according to another modification. The example shown in Figure 5 differs from the example shown in Figure 2 in that the gas supply unit 20 is a supply pipe extending horizontally from the side wall 12S of the vessel 12. In addition, in the case of the gas supply unit 20 shown in Figure 5, the supply holes 21 are formed on the circumferential surface of the supply pipe, rather than at the tip of the supply pipe. This allows the non-oxidizing gas to be supplied from the gas supply unit 20 to the upper space UP in a supply direction Ds toward the surface SF of the contents.

[0046] The example shown in Figure 5 can be suitably used, for example, when some components are provided on the ceiling portion 11 of the melting furnace 10 and the gas supply unit 20 cannot be installed on the ceiling portion 11, or when it is not desirable to install a component on the ceiling portion 11.

[0047] In this way, as long as the supply direction Ds of the oxidizing gas is directed toward the surface SF of the contents, the installation location of the gas supply unit 20 may be the ceiling portion 11 or the side wall 12S of the tank 12.

[0048] Fig. 6 shows a cross-sectional view taken along the z-direction of the molten glass manufacturing apparatus 1 equipped with a gas supply unit 20 according to yet another modified example, and Fig. 7 shows a cross-sectional view taken along line II-II in Fig. 6. In the example shown in Figs. 6 and 7, the molten glass manufacturing apparatus 1 is equipped with two gas supply units 20a and 20b. The two gas supply units 20a and 20b are provided at positions away from the center line CL along the vertical direction of the tank 12 or the molten glass manufacturing apparatus 1. Such an arrangement of the gas supply units is preferable, for example, in a configuration in which another component is provided near the center of the ceiling portion 11 and it is difficult to provide a gas supply unit.

[0049] 6 and 7, gas supply units 20a and 20b are also configured to supply non-oxidizing gas in supply directions Dsa and Dsb, respectively, toward surface SF of the contents. Therefore, the flow of supplied non-oxidizing gas is more likely to impinge on surface SF of the contents and less likely to impinge on the inner surface of side wall 12S of tank 12, thereby ensuring the effect of preventing foreign matter adhering to the inner surface of tank 12 from detaching.

[0050] However, as shown in the example of Figure 6, when the supply directions Dsa and Dsb form a relatively large angle with respect to the vertical direction, for example, an angle greater than 30°, the above-mentioned effect of preventing the detachment of foreign matter adhering to the inner surface of the tank 12 may be smaller than when the supply direction of the non-oxidizing gas is vertical. In contrast, in the examples shown in Figures 6 and 7, the supply directions Dsa and Dsb of the gas supply units 20a and 20b can be made to approximately intersect. This causes the flows of non-oxidizing gas discharged from the gas supply units 20a and 20b to collide with each other, reducing the amount of gas that strikes the inner surface of the side wall 12S of the tank 12 and enhancing the effect of preventing the detachment of foreign matter adhering to the inner surface of the tank 12. In addition, the supply directions Dsa and Dsb approximately intersecting may include not only that the imaginary lines Lsa and Lsb drawn along the supply directions Dsa and Dsb, respectively, intersect, but also that the shortest distance between the imaginary lines Lsa and Lsb is less than twice the inner diameter of the supply holes 21a and 21b of the gas supply sections 20a and 20b (if the inner diameters of the supply holes 21a and 21b are different, the average value), preferably less than the inner diameter.

[0051] Furthermore, when multiple gas supply units are arranged in the ceiling 11, they may be arranged in point symmetry with respect to the centroid of the cross-sectional shape of the upper space UP when viewed in a cross section taken along the x-y plane at the positions of the supply holes of the gas supply units. For example, as shown in Figure 7, both of the two gas supply units 20a and 20b may be located on a line passing through the center of the circle that is the cross-sectional shape of the upper space UP, i.e., the center line CL of the tank 12.

[0052] FIG. 8 shows a modified molten glass manufacturing apparatus 1. In the example shown in FIG. 8, the configuration of the precious metal vessel 15 in the molten glass manufacturing apparatus is different from the example shown in FIG. 2. More specifically, the molten glass manufacturing apparatus 1 shown in FIG. 8 has a crucible-shaped precious metal vessel 15, preferably a platinum vessel, arranged away from the side wall 12S of the vessel 12. Such a crucible-shaped precious metal vessel 15 is also called a pot furnace. The molten glass manufacturing apparatus 1 equipped with the crucible-shaped precious metal vessel 15 is suitable for batch-type molten glass manufacturing. Furthermore, the precious metal vessel 15 shown in FIG. 8 can be used not only in the melting step (S11) of the molten glass manufacturing process (S10), but also in subsequent processing steps, i.e., the fining step (S12) and the homogenization step (S13). The molten glass manufacturing apparatus 1 including a pot furnace as the precious metal vessel 15 provides a melting method that is less affected by the characteristics of the molten glass.

[0053] 8 , the supply direction Ds of the non-oxidizing gas supplied from the gas supply unit 20 to the upper space UP is directed toward the surface SF of the contained items, and more specifically, an imaginary line Ls drawn along the supply direction Ds intersects with the surface SF of the contained items. This makes it easier for the flow of non-oxidizing gas to impinge on the surface SF of the contained items and less likely to impinge on the inner surface of the side wall 12S of the tank 12 or the inner surface of the precious metal tank 15, or both, thereby ensuring the effect of preventing the detachment of foreign matter adhering to the inner surface of the tank 12 or the inner surface of the precious metal tank 15.

[0054] In the above explanation, the apparatus used mainly in the melting step (S11) has been described, but the molten glass manufacturing apparatus according to the present disclosure may be an apparatus used in one or more of the fining step (S12) and the homogenizing step (S13). In this case, the molten glass manufacturing apparatus may be provided with a known apparatus configuration required for the fining step (S12) and the homogenizing step (S13).

[0055] Furthermore, the above-described embodiments may be combined with one another in any desired manner. For example, one or more of the gas supply unit configurations shown in Figures 4 to 7 may be applied to the molten glass manufacturing apparatus shown in Figure 8.

[0056] The embodiments of the present disclosure will be further described below based on experimental examples. Examples 1 to 4 are working examples, and Example 5 is a comparative example.

[0057] <Production of Molten Glass> = Molten Glass Manufacturing Apparatus = In this experiment, the molten glass manufacturing apparatus shown in FIG. 9 was used. The molten glass manufacturing apparatus included two ceiling gas supply units 20 (only one of which is shown in FIG. 9 ) installed in the ceiling 11 and eight sidewall gas supply units 20' (only two of which are shown in FIG. 9 ) installed in the sidewall 12S. Platinum was provided on the entire inner surface of the lower portion of the vessel 12, forming a platinum vessel 15. Two ceiling gas supply units 20 were arranged at the center of the platinum vessel 15 in the x direction, with the gas supply direction Ds oriented toward the contents, and equally spaced in the y direction. The eight sidewall gas supply units 20' were all oriented such that the gas supply direction Ds' was aligned along the x direction (horizontal direction), with four on one side of the x direction and four on the other side, equally spaced in the y direction on each side. The four pairs of sidewall gas supply units 20' facing each other along the x direction were arranged so that their gas supply directions Ds' faced each other. The ceiling gas supply unit 20, whose supply direction Ds was directed toward the contents, was an alumina tube with an inner diameter of 30 mm, and both sidewall gas supply units 20' were alumina tubes with an inner diameter of 12 mm. Each tube had a tip end face perpendicular to the axis of the tube, with an opening formed along this tip end face. The flow rates of the gas supplied from the ceiling gas supply unit 20 and the sidewall gas supply unit 20' were independently adjustable. A heater (not shown) capable of heating the interior of the vessel 12 to 1500°C or higher was located inside the sidewall 12S. The ambient temperature in the upper space UP, measured by the temperature sensor T, was adjusted to between 850°C and 1130°C. The oxygen concentration in the upper space measured by the oxygen concentration sensor C was set to 4.0% by volume or less.

[0058] =Glass Raw Materials= As glass raw materials, glass raw materials M1 and M2 made of alkali-free silicate glass were used. Both glass raw materials M1 and M2 contained SiO ２ , B ２ O ３ , Al ２ O ３ The raw materials contained MgO, CaO, SrO, and BaO, but the contents of each component were different.

[0059] (Example 1) A glass raw material M1 was introduced into the melting tank from a raw material supply port (not shown) and melted to produce molten glass. At that time, nitrogen (N ２ ) gas was supplied simultaneously from the ceiling gas supply unit 20 and eight sidewall gas supply units 20'. The flow rates of the gas supplied from the eight sidewall gas supply units 20' were the same. Table 1 shows, as approximate values, the gas supply rate F1 from the ceiling gas supply unit 20 and the gas supply rate F2 from the sidewall gas supply unit 20' as the ratio of the volume of nitrogen gas supplied per minute to the volume of the upper space.

[0060] (Examples 2 to 6) Molten glass was produced in the same manner as in Example 1, except that the glass raw materials were changed and the flow rate and supply amount of the gas supplied from the ceiling gas supply unit 20 and the flow rate and supply amount of the gas supplied from the side wall gas supply unit 20′ were changed as shown in Table 1.

[0061] <Evaluation> The molten glass obtained in each example was refined and homogenized, and then subjected to a plate-forming process to form a glass plate having a thickness of 5 mm or less, followed by annealing. The obtained glass plate was cut into a size of 30 mm length x 30 mm width, and ten 5 mm square observation areas spaced apart from each other were marked on one main surface. Each observation area was observed using a stereomicroscope, and the number of foreign particles identified was counted. The weight of the glass plate in each example was measured, and the number of foreign particles per weight, i.e., the foreign particle density, was determined under the same conditions. Table 1 shows the values ​​when the foreign particle density of Example 5 (Comparative Example) was set to 1.

[0062]

[0063] As shown in Table 1, it was found that in Examples 1 to 4, in which gas was supplied from the ceiling gas supply unit 20 in a direction toward the surface of the contents of the vessel, the density of platinum foreign matter could be reduced compared to Example 5, in which the gas supply was not directed toward the surface of the contents of the vessel. The oxygen concentration in the upper space was measured in each example. The oxygen concentration in the upper space in Examples 1 and 5 was both 2.0% by volume. The oxygen concentration in the upper space in Example 2 was 2.1% by volume.

[0064] Although the present disclosure has been described above based on the embodiments, the present disclosure is not limited to these embodiments. Furthermore, the above embodiments can be subject to various changes, modifications, substitutions, additions, deletions, and combinations within the scope of the claims, and these also fall within the technical scope of the present invention.

[0065] According to the present invention, it is possible to provide a technique for suppressing the inclusion of foreign matter originating from the constituent material of the tank in a glass article.

[0066] REFERENCE SIGNS LIST 1 Molten glass manufacturing apparatus 10 Melting furnace 11 Ceiling portion 12 Tank 12S Side wall 12B Bottom portion 15 Noble metal tank 20 Gas supply portion 21 Gas supply hole Ds Supply direction Ls Extension line of center line of gas supply hole

Claims

1. A method for producing molten glass, in which molten glass to be subjected to a subsequent forming process is obtained from glass raw materials, comprising supplying a non-oxidizing gas to an upper space of a vessel containing an object containing molten glass in a supply direction toward the surface of the object.

2. The method for producing molten glass according to claim 1, wherein an imaginary line drawn along the supply direction intersects with the surface of the contained object.

3. A method for producing molten glass according to claim 1, wherein the non-oxidizing gas is supplied from a gas supply section provided in a ceiling section covering the upper space of the tank.

4. The method for producing molten glass according to claim 1, wherein the non-oxidizing gas is supplied in a plurality of different supply directions, and the plurality of supply directions include at least two supply directions that approximately intersect with each other.

5. The method for producing molten glass according to claim 1, wherein the material comprising the vessel includes platinum.

6. A method for producing molten glass as described in claim 1, wherein the amount of non-oxidizing gas supplied in the supply direction toward the surface of the contained object is 50% or more and 125% or less as a ratio of the volume of non-oxidizing gas supplied per minute to the volume of the upper space UP.

7. A method for producing molten glass as described in claim 1, wherein the ratio of the amount of non-oxidizing gas supplied in the supply direction toward the surface of the contained object to the total amount of non-oxidizing gas supplied into the upper space is 40% or more.

8. The method for producing molten glass according to claim 1, wherein the oxygen concentration in the non-oxidizing gas is 5% by volume or less.

9. The method for producing molten glass according to claim 1, wherein the non-oxidizing gas comprises at least one selected from the group consisting of nitrogen gas, hydrogen gas, carbon dioxide, and argon gas.

10. A glass manufacturing method comprising a molding step of forming the molten glass obtained by the molten glass manufacturing method according to any one of claims 1 to 9 to obtain a glass article.

11. A molten glass manufacturing apparatus for obtaining molten glass from glass raw materials to be supplied to a subsequent forming device, the apparatus comprising: a vessel in which contents including molten glass are accommodated; and a gas supply unit for supplying a non-oxidizing gas to an upper space of the vessel, wherein the supply direction of the non-oxidizing gas from the gas supply unit is a direction toward the surface of the contents.

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