JP7625178B2 - Method for manufacturing glass articles - Google Patents

Description

This disclosure relates to a method for manufacturing glass articles.

As is well known, glass articles such as glass sheets, glass tubes, and glass fibers are manufactured by heating and melting glass raw materials in a glass melting furnace, and forming the resulting molten glass into a desired shape. Examples of glass melting furnaces include fully electric melting furnaces (see Patent Document 1), which heat only with electrodes immersed in the molten glass in the furnace, and furnaces that use both electrodes and combustion burners for heating.

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

JP 2003-183031 A JP 2016-74598 A

However, when using a full-electric melting furnace to manufacture glass articles, the following problems can occur when using glass raw materials containing tin oxide powder.

In other words, because an all-electric melting furnace does not use a combustion burner for heating, the temperature in the upper space inside the furnace is low, which means that some of the tin oxide powder tends to remain unmelted. This can result in granular tin defects in the manufactured glass products.

In view of the above, the technical problem to be solved is to prevent defects in glass articles when using glass raw materials containing tin oxide powder to manufacture glass articles using an all-electric melting furnace.

The method for manufacturing a glass article to solve the above problem includes a melting step in which a glass raw material containing tin oxide powder is supplied onto molten glass contained in a glass melting furnace, and the supplied glass raw material is heated and melted by 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 taken and passed through a 140 mesh sieve of ASTM Standard E11, has a mass of 0.01 g or less remaining on the sieve.

In this method, the tin oxide powder used is one in which, when 100 g of the powder is taken and passed through a 140 mesh sieve of ASTM standard 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 effectively prevent the tin oxide powder from remaining unmelted during the melting process. As a result, the occurrence of defects in the glass article can be avoided.

In the above method, it is preferable to use tin oxide powder with a median diameter D50 of 1 μm to 80 μm.

If the median diameter D50 is too small, the particles contained in the tin oxide powder will be correspondingly fine, and since the cost of producing such fine particles will be high, the production cost of the glass raw material containing the tin oxide powder will tend to increase as a result. On the other hand, if the median diameter D50 is too large, it will be difficult to meet 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 will be easier to meet the above-mentioned condition while preventing an increase in the production cost of the glass raw material.

In the above method, it is preferable to use tin oxide powder with a median diameter D50 of more than 50 μm to 80 μm.

In this way, the production cost of glass raw materials can be reduced because the median diameter D50 is more than 50 μm. Furthermore, since the tin oxide powder is less likely to contain excessively fine particles, it becomes easier to handle the glass raw materials, for example, by making it easier to feed the raw materials with a feeder when supplying them to a glass melting furnace.

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% SnO ₂ .

This allows air bubbles to be effectively removed from the molten glass.

In the above method, the glass raw materials may be prepared so that the molten glass contains, by mass%, SiO ₂ : 50% to 70%, Al ₂ O ₃ : 12% to 25%, B ₂ O ₃ : 0% to 12%, Li ₂ O + Na ₂ O + K ₂ O (total amount of Li ₂ O, Na ₂ O, and K ₂ O): 0% to less than 1%, MgO: 0% to 8%, CaO: 0% to 15%, SrO: 0% to 12%, and BaO: 0% to 15%.

In this way, when manufacturing glass substrates for displays as glass articles, it is possible to enjoy the effect of avoiding the occurrence of defects.

In the above method, the cullet ratio of the glass raw material may be 40% or less.

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, if the cullet ratio is 40% or less, and tin oxide powder is used such that the mass remaining on the sieve is 0.01 g or less per 100 g, the effect of avoiding defects can be advantageously enjoyed.

In the above method, the temperature corresponding to a viscosity of 10 ^2.5 Pa·s in the molten glass may be 1630° C. or lower.

When the molten glass satisfies the above temperature conditions, defects are likely to occur in the glass product due to unmelted tin oxide powder. Therefore, when the above conditions are met, the effect of avoiding the occurrence of defects can be advantageously achieved by using tin oxide powder that has a mass remaining on the sieve of 0.01 g or less per 100 g.

According to the above-mentioned method for manufacturing glass articles, when glass raw materials containing tin oxide powder are used to manufacture glass articles using a full electric melting furnace, it is possible to avoid the occurrence of defects in the glass articles.

1 is a cross-sectional view showing a method for manufacturing a glass article. FIG. 1 is a schematic diagram showing a method for manufacturing a glass article.

The manufacturing method of a glass article according to the embodiment will be described below with reference to the attached drawings. First, the glass melting furnace used in this manufacturing method will be described.

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. This glass melting furnace 1 is configured to carry out a melting process P1 in which glass raw material 4 supplied onto the surface 2a of the molten glass 2 in the melting chamber 3 is heated and melted, and to cause the molten glass 2 produced by the melting process P1 to flow out of the melting chamber 3.

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

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 (SnO ₂ ) 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 SnO ₂ , and may contain impurities that are inevitably mixed in during the manufacturing process or handling process. For example, the SnO ₂ content of the tin oxide powder is 98% by mass or more.

On the bottom wall 3e, a plurality of rod-shaped electrodes 7 for heating the molten glass 2 by passing an electric current therethrough are installed in a state immersed in the molten glass 2. Also, on each of the pair of side walls 3c, a plurality of plate-shaped electrodes 8 for heating the molten glass 2 by passing an electric current therethrough are installed in a state immersed in the molten glass 2. As these electrodes 7, 8 heat the molten glass 2, the glass raw material 4 on the surface 2a of the molten glass 2 is indirectly heated and gradually melts.

In the glass melting furnace 1, after the start of continuous production of the molten glass 2 (after the start of the melting process P1), the thermal energy applied to the molten glass 2 in the melting chamber 3 is generated only by the electrodes 7 and 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 raw material 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 process P1 can be performed), the molten glass 2 and/or the glass raw material 4 may be heated, for example, by a combustion burner (not shown) installed on the side wall 3c.

From the viewpoint of promoting a reduction in the moisture content of the glass, a reduction in greenhouse gas emissions, and a reduction in the energy required for melting, it is preferable to produce molten glass 2 using a single glass melting furnace 1 in the melting process P1, rather than using multiple glass melting furnaces 1. From the viewpoint of promoting a reduction in greenhouse gas emissions and a reduction in the 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.

β-OH can be used as an indicator of the water content of glass. By lowering this β-OH, the strain point can be increased. Furthermore, even if the glass composition is the same, the smaller the β-OH, the smaller the thermal shrinkage at temperatures 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.

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

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

The following describes a method for manufacturing a glass article using the above-mentioned glass melting furnace 1. In this embodiment, an example is given of manufacturing a glass substrate for a display as the glass article.

In this manufacturing method, as described above, glass raw material 4 containing tin oxide powder is supplied onto molten glass 2 contained 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, and 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. In other words, because the particles of tin oxide powder tend to aggregate, the tin oxide powder remaining on the sieve is pressed against the mesh 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."

From the viewpoint of preventing an increase in the production cost of glass raw material 4 containing tin oxide powder and from the viewpoint of making it easier to satisfy 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 weighing and transportation of glass raw material 4.

The glass frit 4 has a cullet rate of 40% or less. The glass frit 4 is prepared so that when the glass frit 4 is melted to produce the molten glass 2, the molten glass 2 contains 0.01% to 1.5% SnO ₂ by mass%. The glass frit 4 is prepared so that when the molten glass 2 is produced, the molten glass 2 contains SiO ₂ : 50% to 70%, Al ₂ O ₃ : 12% to 25%, B ₂ O ₃ : 0% to 12%, Li ₂ O + Na ₂ O + K ₂ O (total amount of Li ₂ O, Na ₂ O, and K ₂ O): 0% to less than 1%, MgO: 0% to 8%, CaO: 0% to 15%, SrO: 0% to 12%, and BaO: 0% to 15% by mass%. In addition, in this molten glass 2, the temperature corresponding to a viscosity of 10 ^2.5 Pa·s is 1630° C. or lower.

As shown in FIG. 2, the molten glass 2 produced in the glass melting furnace 1 by carrying out the melting process P1 then undergoes the fining process P2, the stirring process P3, the conditioning process P4, and the forming process P5 in sequence.

The fining step P2 is carried out in a fining tank 9. In the fining tank 9, the molten glass 2 that flows into the fining tank 9 from the glass melting furnace 1 is heated while a fining agent (tin oxide powder) is used to remove air bubbles from the molten glass 2.

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 flows from the fining tank 9 into the stirring tank 10 is stirred by the stirrer 11 to homogenize the molten glass 2.

The conditioning step P4 is carried out using the conditioning tank 12. In the conditioning tank 12, the temperature (viscosity) and flow rate of the molten glass 2 are adjusted to make the molten glass 2 suitable for forming.

A forming body 13 is used to perform the forming step P5. In the forming body 13, the molten glass 2 is continuously formed into a glass ribbon 14 by the overflow downdraw method. Note that the forming body 13 may be one that forms the glass ribbon 14 by other forming methods such as the slot downdraw method, the redraw method, or the float method.

Then, various processes are carried out, such as a cutting process in which the glass plate that will become the glass substrate is cut out from the formed glass ribbon 14, a grinding and polishing process for the glass plate, a cleaning process, and an inspection process, to manufacture a glass substrate for a display. Note that in this embodiment, a glass substrate for a display is manufactured as the glass article, but it is of course possible to manufacture other glass articles (e.g., glass tubes, glass fibers, etc.).

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 the 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 manufactured were examined to see whether defects (granular tin) caused by undissolved tin oxide powder were present. Specifically, the number of defects caused by undissolved tin oxide powder and 10 μm or longer in length were counted.

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

As the results shown in [Table 1] show, in Examples 1 to 3, unlike the Comparative Example, it was possible to avoid the occurrence of defects in the glass substrate. It is presumed that such results were obtained because, unlike the Comparative Example, in Examples 1 to 3, it was possible to effectively prevent the unmelted tin oxide powder from remaining in the melting step P1. In addition, when glass substrates were manufactured using glass raw material 4 of the Comparative Example and glass raw material 4 of Examples 1 to 3, respectively, and using a furnace that uses electrodes and combustion burners in combination, rather than the above-mentioned glass melting furnace 1, which is an all-electric melting furnace, no defects occurred in any case.

Reference Signs List 1 Glass melting furnace 2 Molten glass 4 Glass raw material 7 Electrode 8 Electrode P1 Melting process

Claims (5)

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 . The method for manufacturing a glass article according to claim 1 , characterized in that the glass raw materials are mixed so that the molten glass contains, by mass%, 0.01% to 1.5% SnO ₂ . The method for manufacturing a glass article according to claim ₁ or 2, characterized in that the glass raw materials are blended so that the molten glass contains, by mass%, SiO ₂ : 50% to 70%, Al ₂ O ₃ : 12% to 25%, B ₂ O ₃ : 0% to 12%, Li ₂ O + Na 2 O + _K 2 O (total amount of Li ₂ O, Na ₂ O, and K ₂ O): 0% to less than 1%, MgO: 0% to 8%, CaO: 0% to 15%, SrO: 0% to 12%, and BaO: 0% to 15%. 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. The method for producing a glass article according to claim 1, wherein a temperature corresponding to a viscosity of 10 ^2.5 Pa·s in the molten glass is 1630° C. or lower.

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