Method for manufacturing glass articles

Abstract

To avoid a defect of a glass article when using a glass raw material including tin oxide powder in using a fully electric melting furnace to manufacture the glass article.SOLUTION: A method of manufacturing a glass article that comprises a melting process of: supplying a glass raw material 4 including tin oxide powder onto molten glass 2 put in a glass melting furnace 1; and heating and melting the supplied glass raw material 4 by electrodes 7, 8 dipped in the molten glass 2, wherein less than 0.01 g mass of the powder in use leaves on a sieve of 140 meshes defined by ASTM standard E11 when the tin oxide power is sampled by 100 g and passed through the sieve.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a method for manufacturing a glass article. [Background technology]

[0002] As is well known, glass articles such as glass sheets, glass tubes, glass fibers, etc. are manufactured by heating and melting glass raw materials in a glass melting furnace, and forming the resulting molten glass into a predetermined shape. Examples of glass melting furnaces include all-electric melting furnaces (see Patent Document 1) in which heating is performed only by electrodes immersed in the molten glass in the furnace, and furnaces in which heating is performed by using both electrodes and combustion burners.

[0003] Glass raw materials contain a fining agent for removing bubbles from molten glass, and tin oxide (SnO2) powder is widely used as the fining agent. For example, Patent Document 2 discloses the use of tin oxide powder with a median diameter D50 of 2 μm to 9 μm in order to produce a glass article with excellent bubble quality. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2003-183031 A [Patent Document 2] JP 2016-74598 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, when a glass raw material containing tin oxide powder is used in producing a glass article using an all-electric melting furnace, the following problems may arise.

[0006] In other words, since the all-electric melting furnace does not use a combustion burner for heating, the temperature in the upper space of the furnace is low, and as a result, some of the tin oxide powder tends to remain unmelted. This can result in granular tin defects in the manufactured glass products.

[0007] In view of the above circumstances, a technical problem to be solved is to prevent the occurrence of defects in a glass article when a glass raw material containing tin oxide powder is used in producing a glass article using an all-electric melting furnace. [Means for solving the problem]

[0008] A method for manufacturing a glass article for solving the above problems includes a melting step of supplying a glass raw material containing tin oxide powder onto molten glass contained in a glass melting furnace, and heating and melting the supplied glass raw material with an electrode immersed in the molten glass, and is characterized in that the tin oxide powder used is a powder that, when 100 g of the powder is sampled and passed through a 140 mesh sieve of ASTM Standard E11, has a mass of 0.01 g or less remaining on the sieve.

[0009] In this method, the tin oxide powder used is one that, when 100 g of the powder is taken and passed through a 140 mesh sieve of ASTM E11, the mass remaining on the sieve is 0.01 g or less. When such a tin oxide powder is used, it is possible to suitably prevent the tin oxide powder from remaining undissolved in the melting process. As a result, the occurrence of defects in the glass article can be avoided.

[0010] In the above method, it is preferable to use, as the tin oxide powder, a powder having a median diameter D50 of 1 μm to 80 μm.

[0011] If the median diameter D50 is too small, the particles contained in the tin oxide powder are accordingly fine, and the cost of producing such fine particles is high, which results in an increase in the production cost of the glass raw material containing the tin oxide powder. On the other hand, if the median diameter D50 is too large, it becomes difficult to satisfy the condition that the mass remaining on the sieve is 0.01 g or less per 100 g. However, if the median diameter D50 is 1 μm to 80 μm, it becomes easy to satisfy the above-mentioned condition while preventing an increase in the production cost of the glass raw material.

[0012] In the above method, it is preferable to use, as the tin oxide powder, a powder having a median diameter D50 of more than 50 μm and up to 80 μm.

[0013] In this way, the production cost of the glass raw material can be reduced by making the median diameter D50 more than 50 μm. Furthermore, since the tin oxide powder is unlikely to contain excessively fine particles, it becomes possible to easily handle the glass raw material, for example, to easily feed the raw material with a feeder when supplying the glass raw material to a glass melting furnace.

[0014] In the above method, it is preferable to prepare glass raw materials so that the molten glass contains, by mass%, 0.01% to 1.5% SnO2.

[0015] In this way, air bubbles can be suitably removed from the molten glass.

[0016] In the above method, the glass raw materials may be prepared so that the molten glass contains, by mass%, SiO2: 50% to 70%, Al2O3: 12% to 25%, B2O3: 0% to 12%, Li2O+Na2O+K2O (total amount of Li2O, Na2O, and K2O): 0% to less than 1%, MgO: 0% to 8%, CaO: 0% to 15%, SrO: 0% to 12%, and BaO: 0% to 15%.

[0017] In this way, when a glass substrate for a display is manufactured as the glass article, it is possible to enjoy the effect of preventing the occurrence of defects.

[0018] In the above method, the glass raw material may have a cullet rate of 40% or less.

[0019] The lower the cullet ratio of the glass raw material, the more likely defects will occur in the glass product due to unmelted tin oxide powder. Therefore, when the cullet ratio is 40% or less, by using a tin oxide powder whose mass remaining on the sieve is 0.01 g or less per 100 g, the effect of avoiding defects can be advantageously enjoyed.

[0020] In the above method, the viscosity of the molten glass is 10 2.5 The temperature corresponding to Pa·s may be 1630° C. or less.

[0021] When the molten glass satisfies the above-mentioned temperature conditions, defects are likely to occur in the glass product due to unmelted tin oxide powder. Therefore, when the above-mentioned conditions are satisfied, the effect of avoiding the occurrence of defects can be advantageously enjoyed by using a tin oxide powder whose mass remaining on the sieve is 0.01 g or less per 100 g. Effect of the Invention

[0022] According to the above-mentioned method for manufacturing a glass article, when a glass raw material containing tin oxide powder is used in manufacturing a glass article using a full electric melting furnace, it is possible to avoid the occurrence of defects in the glass article. [Brief description of the drawings]

[0023] [Figure 1] 1 is a cross-sectional view showing a method for manufacturing a glass article. [Diagram 2] FIG. 1 is a schematic diagram showing a method for manufacturing a glass article. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] Hereinafter, a method for manufacturing a glass article according to an embodiment will be described with reference to the accompanying drawings. First, a glass melting furnace used in the manufacturing method will be described.

[0025] The glass melting furnace 1 shown in Fig. 1 is a fully electric melting furnace equipped with a melting chamber 3 capable of accommodating molten glass 2. The glass melting furnace 1 is configured to carry out a melting step P1 in which glass raw material 4 supplied onto a surface 2a of molten glass 2 in the melting chamber 3 is heated and melted, and to cause the molten glass 2 produced in the melting step P1 to flow out of the melting chamber 3.

[0026] The melting chamber 3 has a front wall 3a located at an upstream end in a flow direction D of the glass raw material 4 (molten glass 2) in the melting chamber 3, a rear wall 3b located at a downstream end, a pair of side walls 3c (only one of the pair is shown in FIG. 1), a ceiling wall 3d, and a bottom wall 3e.

[0027] The front wall 3a is provided with a screw feeder 5 for continuously supplying the frit 4. The frit 4 supplied from the screw feeder 5 melts while flowing in the flow direction D on the surface 2a of the molten glass 2. As a result, a part of the surface 2a is covered with the frit 4. As will be described later in detail, the frit 4 contains tin oxide (SnO2) powder as a fining agent. The rear wall 3b is provided with an outlet 6 for continuously flowing out the molten glass 2. Here, the tin oxide powder means a powder mainly composed of SnO2, and may contain impurities that are inevitably mixed in during the manufacturing process or handling process. For example, the SnO2 content of the tin oxide powder is 98 mass% or more.

[0028] A plurality of rod-shaped electrodes 7 for heating molten glass 2 by passing an electric current therethrough are disposed on bottom wall 3e in a state where they are immersed in molten glass 2. A plurality of plate-shaped electrodes 8 for heating molten glass 2 by passing an electric current therethrough are disposed on each of paired side walls 3c in a state where they are immersed in molten glass 2. As these electrodes 7, 8 heat molten glass 2, glass raw material 4 on surface 2a of molten glass 2 is indirectly heated and gradually melts.

[0029] In the glass melting furnace 1, after the start of continuous production of the molten glass 2 (after the start of the melting step P1), the thermal energy to be applied to the molten glass 2 in the melting chamber 3 is generated only by the electrodes 7, 8. This makes it possible to suppress an increase in the moisture content of the molten glass 2 in the melting chamber 3, and to reduce the moisture content of the resulting glass (glass product). In addition, the molten glass 2 can be produced at a low temperature in the upper space of the furnace without heating with a combustion burner. This makes it possible to reduce the emission of greenhouse gases and the energy required to melt the glass frit 4. Note that, in the stage before the start of continuous production (the stage of starting up the furnace to a state where the melting step P1 can be performed), the molten glass 2 and / or the glass frit 4 may be heated, for example, by a combustion burner (not shown) installed on the side wall 3c.

[0030] From the viewpoint of promoting reduction in the moisture content of glass, reduction in greenhouse gas emissions, and reduction in energy required for melting, it is preferable to produce molten glass 2 using a single glass melting furnace 1 in the melting step P1, without using multiple glass melting furnaces 1. From the viewpoint of promoting reduction in greenhouse gas emissions and reduction in energy required for melting, it is preferable that the maximum temperature of molten glass 2 in the glass melting furnace 1 is 1400°C to 1700°C, and the residence time of molten glass 2 in the glass melting furnace 1 is 2 hours to 240 hours.

[0031] β-OH can be used as an index of the water content of glass. By decreasing this β-OH, the strain point can be increased. Even if the glass composition is the same, the smaller the β-OH, the smaller the thermal shrinkage at a temperature below the strain point. β-OH is preferably 0.30 / mm or less, 0.25 / mm or less, 0.20 / mm or less, 0.15 / mm or less, and particularly 0.10 / mm or less. If β-OH is too small, the melting property is likely to decrease. Therefore, β-OH is preferably 0.01 / mm or more, and particularly 0.03 / mm or more.

[0032] Here, "β-OH" refers to a value obtained by measuring the transmittance of glass using FT-IR and using the following mathematical formula 1.

[0033] [Number 1] β-OH=(1 / X)log(T1 / T2) X: Plate thickness (mm) T1: Transmittance (%) at reference wavelength 3846 cm-1 T2: Minimum transmittance (%) at hydroxyl group absorption wavelength of 3600 cm-1

[0034] Hereinafter, there will be described a method for manufacturing a glass article using the above-mentioned glass melting furnace 1. In this embodiment, a case where a glass substrate for a display is manufactured as a glass article will be taken as an example.

[0035] In this manufacturing method, as described above, glass raw material 4 containing tin oxide powder is supplied onto molten glass 2 accommodated in glass melting furnace 1. As the tin oxide powder, in order to prevent the tin oxide powder from remaining unmelted in melting step P1, when 100 g of tin oxide powder is collected and passed through a 140 mesh sieve (a sieve with an opening of 105 μm) of ASTM standard E11, the mass of the tin oxide powder remaining on the sieve is 0.01 g or less. The mass of the tin oxide powder remaining on the sieve is preferably 0.005 g or less, more preferably 0.001 g or less. On the other hand, the lower limit of the mass of the tin oxide powder remaining on the sieve can be 0 g. The "tin oxide powder remaining on the sieve" referred to here means the following tin oxide powder. That is, since the particles of tin oxide powder tend to aggregate, the tin oxide powder remaining on the sieve is pressed against the meshes of the sieve to take this into consideration, and the tin oxide powder that still does not pass through the sieve is referred to as "tin oxide powder remaining on the sieve."

[0036] From the viewpoint of preventing an increase in the production cost of the glass raw material 4 containing the tin oxide powder and from the viewpoint of easily satisfying the above-mentioned condition that the mass remaining on the sieve is 0.01 g or less per 100 g, the median diameter D50 of the tin oxide powder is set to 1 μm to 80 μm. Preferably, the median diameter D50 is set to more than 50 μm to 80 μm. This makes it possible to stabilize the measurement and transportation of the glass raw material 4.

[0037] The glass raw material 4 has a cullet rate of 40% or less. The glass raw material 4 is prepared so that when the glass raw material 4 is melted to produce the molten glass 2, it contains 0.01% to 1.5% SnO2 by mass%. The glass raw material 4 is prepared so that when the molten glass 2 is produced, it contains 50% to 70% SiO2, 12% to 25% Al2O3, 0% to 12% B2O3, 0% to less than 1% Li2O+Na2O+K2O (total amount of Li2O, Na2O, and K2O), 0% to 8% MgO, 0% to 15% CaO, 0% to 12% SrO, and 0% to 15% BaO by mass%. The molten glass 2 has a viscosity of 10 2.5The temperature corresponding to Pa·s is below 1630°C.

[0038] As shown in FIG. 2, molten glass 2 produced in a glass melting furnace 1 by carrying out a melting step P1 then sequentially undergoes a fining step P2, a stirring step P3, a conditioning step P4, and a forming step P5.

[0039] The fining step P2 is performed in a fining tank 9. In the fining tank 9, the molten glass 2 that has flowed into the fining tank 9 from the glass melting furnace 1 is heated while air bubbles are removed from the molten glass 2 by the action of a fining agent (tin oxide powder).

[0040] The stirring step P3 is carried out using a stirring tank 10 and a stirrer 11 equipped with stirring blades. Specifically, the molten glass 2 that has flowed from the refining tank 9 into the stirring tank 10 is stirred by the stirrer 11, thereby homogenizing the molten glass 2.

[0041] The conditioning step P4 is carried out using the conditioning tank 12. In the conditioning tank 12, the temperature (viscosity), flow rate, and the like of the molten glass 2 are adjusted so as to bring the molten glass 2 into a state suitable for forming.

[0042] The forming step P5 is performed using a forming body 13. In the forming body 13, the molten glass 2 is continuously formed into a glass ribbon 14 by an overflow downdraw method. Note that the forming body 13 may be one that forms the glass ribbon 14 by other forming methods such as a slot downdraw method, a redraw method, or a float method.

[0043] Thereafter, various processes are carried out, such as a cutting process for cutting out glass plates that will become glass substrates from the formed glass ribbon 14, a grinding and polishing process for the glass plates, a cleaning process, and an inspection process, to manufacture a glass substrate for a display. Note that, although a glass substrate for a display is manufactured as the glass article in this embodiment, it is of course possible to manufacture other glass articles (for example, a glass tube, glass fiber, etc.). EXAMPLES

[0044] In the same manner as the above embodiment, as shown in Table 1 below, four types of tin oxide powder (three types in the example, one type in the comparative example) were used, each of which has a different mass remaining on a sieve when 100 g of the powder was taken and passed through a 140 mesh sieve of ASTM standard E11, to manufacture glass substrates for displays. Then, the 100 kg glass substrates thus manufactured were examined for the presence or absence of defects (granular tin) resulting from the unmelted tin oxide powder. Specifically, the number of defects resulting from the unmelted tin oxide powder and having a length of 10 μm or more was counted.

[0045] Here, in the item for the presence or absence of defects in [Table 1], "◎" means that the number of the defects was 0.01 or less, "○" means that the number of the defects was more than 0.01 and 0.1 or less, "△" means that the number of the defects was more than 0.1 and 0.2 or less, and "×" means that the number of the defects was more than 0.2.

[0046] [Table 1]

[0047] As shown in the results in Table 1, in Examples 1 to 3, it was possible to avoid the occurrence of defects in the glass substrate, unlike the comparative example. It is presumed that such results were obtained because, unlike the comparative example, in Examples 1 to 3, it was possible to suitably prevent the unmelted tin oxide powder in the melting step P1. In addition, when glass substrates were manufactured using glass frit 4 of the comparative example and glass frit 4 of Examples 1 to 3, respectively, and using a furnace using electrodes and a combustion burner in combination, rather than the above-mentioned glass melting furnace 1 which is an all-electric melting furnace, no defects were generated in any of the cases. [Explanation of symbols]

[0048] 1 Glass melting furnace 2 Molten Glass 4. Glass Raw Materials 7 electrodes 8 electrodes P1 Melting process

Claims

1. A method for producing a glass article, comprising a melting step of supplying a glass frit containing tin oxide powder onto molten glass contained in a glass melting furnace, and heating and melting the supplied glass frit with an electrode immersed in the molten glass, The method for producing a glass article uses, as the tin oxide powder, a powder in which, when 100 g of the tin oxide powder is sampled and passed through a 140 mesh sieve of ASTM Standard E11, the mass remaining on the sieve is 0.01 g or less, and the powder has a median diameter D50 of more than 50 μm to 80 μm.

2. The molten glass contains, in mass%, 0.01% to 1.5% SnO ２ The method for producing a glass article according to claim 1, characterized in that the glass raw material is mixed so as to contain

3. The molten glass contains, in mass %, SiO ２ :50%~70%, Al ２ O ３ :12%~25%, B ２ O ３ :0%~12%, Li ２ O+Na ２ O+K ２ O (Li ２ O, Na ２ O and K ２ 3. The method for producing a glass article according to claim 1 or 2, characterized in that the glass raw materials are formulated to contain: 0% to less than 1% of total amount of O, 0% to less than 1%, MgO: 0% to 8%, CaO: 0% to 15%, SrO: 0% to 12%, and BaO: 0% to 15%.

4. The method for producing a glass article according to any one of claims 1 to 3, characterized in that the cullet rate of the glass raw material is 40% or less.

5. Viscosity of the molten glass: 10 ２．５ The method for producing a glass article according to any one of claims 1 to 4, characterized in that the temperature corresponding to Pa·s is 1630° C. or lower.

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