WO2019093231A1 - Method for producing float glass, and apparatus for producing float glass - Google Patents

Abstract

The present invention relates to a method for producing a float glass, wherein: a molten glass that is obtained by melting a glass starting material is shaped into a glass ribbon on a molten tin within a float bath; and the thus-obtained glass ribbon is subjected to slow cooling, thereby obtaining a glass plate. This method for producing a float glass is characterized in that a plasma gas is sprayed to a molten metal exposure part that is exposed to the atmosphere within the float bath.

Description

Method of manufacturing float glass, and apparatus for manufacturing float glass

The present invention relates to a method for producing float glass and a device for producing float glass, which reduce tin defects.

In the production of float glass, it is important to reduce the dissolution of oxygen into the molten tin in the float bath. One of the reasons is that tin oxide produced by the dissolution of oxygen in molten tin adheres to the lower surface of the float glass to cause a tin defect.

In the past, in order to prevent contact between molten tin and oxygen in the float bath, the float bath is sealed as much as possible, and high purity nitrogen gas is blown in as a protective atmosphere gas to prevent the entry of air and is still intruded. At the same time, hydrogen gas is blown in to remove a trace amount of oxygen in the air. The pressure of the protective atmosphere gas in the float bath is set slightly higher than the atmospheric pressure outside the float bath in order to prevent the entry of oxygen in the air.

In recent years, a further reduction in tin defects has been required to improve manufacturing yield. In order to meet this demand, it is necessary to adopt a direct method of removing tin oxide itself in molten tin.

Therefore, Patent Document 1 proposes that a part of molten tin in the tin bath be extracted from the tin bath, reacted and removed from tin oxide in the extracted molten tin, and then returned to the tin bath.

Japanese Patent No. 4281141

However, the method described in Patent Document 1 needs to provide a circulation system for circulating molten tin outside the tin bath, and in order to remove tin oxide in the molten tin, the molten tin is tin bath It is necessary to cool to a temperature below the internal minimum temperature and reheat the molten tin before returning it to the tin bath. Therefore, although the method described in Patent Document 1 can reduce tin defects, there is a problem that equipment configuration and manufacturing conditions become complicated, and equipment investment cost and operation cost increase.

The present invention is made in view of the above-mentioned subject, and an object of the present invention is to provide a manufacturing method of float glass from which a good quality glass board is obtained by simple manufacturing conditions, and a manufacturing apparatus of float glass.

MEANS TO SOLVE THE PROBLEM In order to solve the said subject, this invention shape | molds the molten glass obtained by melt | dissolving glass-making feedstock to a glass ribbon on the molten metal in a float bath, and it anneals the obtained glass ribbon and obtains plate glass. A method of manufacturing float glass, comprising: injecting a plasma gas to a molten metal exposed portion exposed to an atmosphere in the float bath.
In the method of manufacturing float glass according to the present invention, when the distance in the width direction of the molten metal exposed portion is W (mm), the plasma gas is sprayed to the molten metal exposed portion at a width direction distance of 0.3 W or more. Is preferred.
In the method of manufacturing float glass according to the present invention, the plasma gas is preferably jetted to the molten metal exposed portion at a flow direction distance of 10 to 400 mm.
In the method of manufacturing float glass according to the present invention, preferably, the plasma gas is sprayed to the molten metal exposed portion at a distance of 5 to 30 mm above the molten metal exposed portion.
The method of manufacturing a float glass of the present invention, the plasma gas, He, Ne, Ar, N 2, CO, CO 2, H 2, H 2 O, NH 3, CH 4, C 2 H 2, C 2 H It is preferable to contain at least one selected from the group consisting of ₄ and C ₂ H ₆ .
In the method for producing float glass according to the present invention, it is preferable that a hydrogen radical density in an atmosphere until the plasma gas is jetted and reaches the molten metal exposed portion is 1 × 10 ¹¹ / cm ³ or more.
In the method of manufacturing float glass according to the present invention, it is preferable to jet plasma gas at a linear velocity of 0.1 to 200 m / s to the molten metal exposed portion.
In the method of manufacturing float glass according to the present invention, the plasma gas is injected from a plasma injection device provided opposite to the upper side of the molten metal exposed portion,
The plasma injection apparatus includes a plasma gas injection unit that injects plasma gas.
The plasma gas injection unit includes a plurality of plasma generators.
It is preferable that the electron density of the said plasma gas in the plasma-ized area | region which plasmifies the gas introduce | transduced into the said plasma generator is 1 * 10 < ¹³ > / cm < ³ > or more.
In the method for producing float glass according to the present invention, in the molten metal exposed portion, the oxygen potential of the molten metal after the plasma gas injection is not more than half the oxygen potential of the molten metal before the plasma gas injection. preferable.
In the method of producing float glass according to the present invention, the temperature of the molten metal to which plasma gas is injected is preferably 900 ° C. or less.
Moreover, this invention shape | molds the molten glass obtained by melt | dissolving a glass raw material on glass ribbon on the molten metal in a float bath, slow-cools the obtained glass ribbon, and manufactures float glass which obtains plate glass. In the apparatus, a plasma injection device is disposed above the molten metal exposed portion exposed to the atmosphere in the float bath, and the plasma injection device includes a plasma gas injection portion and the plasma gas injection portion. There is provided a float glass manufacturing apparatus comprising: a supporting portion for supporting, wherein the plasma gas injection portion injects plasma gas to the molten metal exposed portion.
In the float glass manufacturing apparatus of the present invention, the plasma gas injection unit includes a plurality of plasma generators.
It is preferable that the plasma generating device is disposed such that the longitudinal direction of the plasma generating device coincides with the flow direction of the glass ribbon.
In the plasma generator of the float glass manufacturing apparatus of the present invention, the cross-sectional shape of the gas discharge part is preferably rectangular.

According to the present invention, good quality float glass can be manufactured under simple manufacturing conditions.

FIG. 1 is a plan view showing a configuration example of the lower structure of the float bath. FIG. 2 is a partial cross-sectional view taken along line II of FIG. 3 (a) and 3 (b) are schematic views of the main part of the plasma injection apparatus, FIG. 3 (a) is a schematic view as viewed from the plane direction, and FIG. 3 (b) is viewed from the cross sectional direction of FIG. FIG. FIG. 4 (a) is a cross-sectional view showing one configuration example of the plasma generator, and FIG. 4 (b) is a partial cross-sectional view taken along line II-II of FIG. 4 (a). FIG. 5 (a) is a cross-sectional view showing another configuration example of the plasma generator, and FIG. 5 (b) is a partial cross-sectional view taken along line III-III of FIG. 5 (a). FIG. 6 is a view showing the SnO ₂ reduction rate of the example of the plate glass temperature of 500 ° C. and the comparative example. FIG. 7 is a view showing SnO ₂ reduction rates of the example of the sheet glass temperature of 625 ° C. and the comparative example. FIG. 8 is a view showing the SnO ₂ reduction rate of the example of the plate glass temperature of 750 ° C. and the comparative example. FIG. 9 is a graph showing the distance dependency between the plasma gas injection site and the injection site of the SnO ₂ reduction rate. FIG. 10 shows the linear velocity dependency of the plasma gas of the SnO ₂ reduction rate. FIG. 11 is a diagram showing the difference in the SnO ₂ reduction rate depending on the presence or absence of the second discharge part of the plasma generator. FIG. 12 is a diagram showing the temporal transition of the oxygen potential of molten tin before and after the injection of plasma gas.

Hereinafter, a method of manufacturing float glass and an apparatus for manufacturing float glass according to an embodiment of the present invention will be described with reference to the drawings.
In the present invention, a molten glass obtained by melting a glass material is formed into a glass ribbon on molten metal in a float bath, and the obtained glass ribbon is gradually cooled to obtain a sheet glass.

FIG. 1 is a plan view showing a configuration example of the lower structure of the float bath, and FIG. 2 is a partial cross-sectional view taken along the line II of FIG.
The illustrated float bath 100 is constituted by a molten metal tank 10 for containing molten tin 20, a roof 12 disposed above the molten metal tank 10, and the like.
The metal contained in the molten metal tank 10 may be a tin alloy, a metal other than tin, or an alloy thereof. The tin alloy is, for example, an alloy of tin and copper. The metal other than tin is, for example, bismuth. Moreover, alloys of metals other than tin are, for example, alloys of bismuth and copper.

The molten glass obtained by melting the glass raw material is continuously supplied onto the molten tin 20 of the molten metal tank 10. The molten glass is made to flow on the molten tin 20 of the molten metal tank 10 and formed into a strip-like glass ribbon G. The glass ribbon G moves in the direction of the arrow in the figure. Hereinafter, in the present specification, the arrow direction in the drawing is referred to as the flow direction of the glass ribbon G, and the direction orthogonal to the arrow direction is referred to as the width direction of the glass ribbon G. Further, in the present specification, “flow direction” and “width direction” correspond to “flow direction of glass ribbon G” and “width direction of glass ribbon G”, respectively.

The molten metal tank 10 includes, from the upstream side in the flow direction of the glass ribbon G, a wide area Z1 having a wide width, an intermediate area Z2 having a narrow width, and a narrow area Z3 having a narrow width in this order. A molten metal in which molten tin 20 is exposed to the atmosphere in the float bath 100 between the glass ribbon G and the side wall of the molten metal tank 10 (hereinafter sometimes referred to as the left and right sides of the glass ribbon G) Exposed portion 22 is present. The plasma injection apparatus 30 is arrange | positioned above the molten metal exposed part 22 which exists in the left-right both sides of the glass ribbon G of narrow area Z3.
The plasma injection device 30 includes a plasma gas injection unit 31 and a support unit 32 that supports the plasma gas injection unit 31. The plasma gas injection unit 31 is provided to protrude below the support unit 32. The plasma gas injection unit 31 is constituted by a plurality of plasma generators 40 a to be described later, and injects a plasmatized gas (hereinafter referred to as a plasma gas) toward the molten metal exposed unit 22. Inside the support portion 32, a pipe for supplying a gas to be converted into plasma to the plasma generator 40a, and a wire for applying a voltage to the electrode of the plasma generator 40a are provided.
The plasma gas injection unit 31 may be provided inside the support unit 32. In this case, the support 32 should have at least a height for housing the plasma generator 40a.

FIG. 3 is a schematic view of the main part of the plasma injection device, FIG. 3 (a) is a schematic view as viewed from the plane direction, and FIG. 3 (b) is a schematic view as viewed from the cross sectional direction of FIG.
The plasma injection device 30 includes a plasma gas injection unit 31 and a support unit 32. The plasma gas injection unit 31 shown in FIG. 3A is configured of eight plasma generators 40a, and the distance in the width direction of the plasma gas injection unit 31 is W1, and the flow direction distance is L1. Here, “the distance in the width direction of the plasma gas injection unit 31” means the distance (length) of the plasma gas injection unit 31 along the width direction of the glass ribbon. Moreover, "the flow direction distance of the plasma gas injection part 31" means the distance (length) of the plasma gas injection part 31 along the flow direction of the glass ribbon.
The plasma generator 40a may be arranged such that the longitudinal direction of the plasma generator 40a and the flow direction of the glass ribbon coincide. In FIG. 3A, the plasma generating devices 40a are arranged in two rows along the flow direction of the glass ribbon and in four rows along the width direction of the glass ribbon.
The plasma generating devices 40a are preferably arranged in 1 to 6 rows along the flow direction of the glass ribbon and in 1 to 15 rows along the width direction of the glass ribbon. In addition, the plasma generation device 40a may be arranged such that the longitudinal direction of the plasma device 40a and the width direction of the glass ribbon coincide with each other. In this case, it is preferable that the plasma generating devices 40a be arranged in 1 to 15 rows along the flow direction of the glass ribbon and in 1 to 6 rows along the width direction of the glass ribbon.
A gap may be provided between the adjacent plasma generation devices 40a along the flow direction or the width direction of the glass ribbon. The gap is preferably as small as possible in order to spray the plasma gas uniformly along the flow direction or width direction of the glass ribbon.
The plasma gas injection unit 31 may replace the whole or a part of the plasma generator 40a with a plasma generator 40b described later.

FIG. 4 (a) is a cross-sectional view showing an example of the configuration of the plasma generator 40a, and FIG. 4 (b) is a partial cross-sectional view taken along line II-II of FIG. 4 (a). In the plasma generator 40a shown in FIG. 4A, a gas introduction unit 42 for introducing a gas to be plasmatized is provided on the top of a housing 41 made of a sintered body such as alumina. Below the gas introduction part 42, there is a plasma conversion region P for converting the introduced gas into plasma. In the plasma conversion region P, two electrodes 44 are inserted at intervals from the side surface of the housing 41, and a predetermined voltage is applied between the electrodes 44 while continuously introducing a gas from the gas introduction unit 42. The introduced gas is plasmified by generating discharge. The gas (plasma gas) converted into plasma is discharged from a gas discharge unit 43 provided at the lower part of the housing 41.
As shown in FIG. 4B, it is preferable that the cross-sectional shape of the gas discharge part 43 is a rectangle whose long side is the longitudinal direction of the electrode 44 and whose short side is a particularly short linear rectangle (slit). . As a result, the reactive species of the plasma gas discharged from the gas discharge unit 43 increase, and the reduction of tin oxide is promoted.

FIG. 5 (a) is a cross-sectional view showing another configuration example of the plasma generator, and FIG. 5 (b) is a partial cross-sectional view taken along line III-III of FIG. 5 (a). In the plasma generator 40 b shown in FIG. 5A, the second discharge unit 45 is provided below the gas discharge unit (first discharge unit) 43. In the second discharge portion 45, a plurality of holes are linearly arranged, and radicals having a uniform density can be jetted along the longitudinal direction of the electrode 44. As shown in FIG. 5B, the cross-sectional shape of the hole provided in the second discharge part 45 is a circle, but it may be a polygon such as an ellipse, a triangle, or a square. Thereby, the discharge phenomenon to the process target object of plasma gas can be suppressed.

In the plasma generator 40b shown in FIG. 5 (b), the ratio of the total cross-sectional area of the holes to the entire lower surface of the plasma generator 40b is preferably 0.01 to 5%.

In the plasma generating devices 40a and 40b shown in FIGS. 4 (a) and 5 (a), the plasma discharge type is preferably a hollow cathode discharge. However, the present invention is not limited to this, and the plasma generation device may be a dielectric barrier discharge (DBD) or arc discharge as a plasma discharge type. Moreover, the high frequency induction discharge which does not use an electrode, and a microwave discharge may be sufficient. In addition, discharge by a high frequency power source may be used.

In the embodiment of the present invention, a plasma gas is injected from the plasma gas injection unit 31 of the plasma injection device 30 to the molten metal exposed unit 22. Thereby, the tin oxide present near the surface of the molten tin 20 is reduced according to the mechanism described below.
As shown in the following formula (1), the oxygen in the atmosphere in the float bath 100 or the oxygen in the molten glass dissolves in the molten tin 20 of the molten metal tank 10, and tin oxide SnO _x (0 <x ≦ 2) will occur.
Sn + O ₂ → SnO _x (1)
The reason why hydrogen gas is blown into the atmosphere in the float bath 100 together with high purity nitrogen gas is that tin oxide SnO _x in molten tin 20 is produced by hydrogen in the atmosphere as shown in the following formula (2). Is reduced to metal tin Sn.
SnO _x + H ₂ → Sn + H ₂ O (g) (2)
When the plasma gas is injected to the molten metal exposed portion 22, hydrogen present in the plasma gas and hydrogen in the atmosphere in the float bath 100 are radicalized or ionized. As a result, hydrogen radicals and hydrogen ions, which are reactive species, are supplied at a higher density, thereby promoting the reaction represented by the formula (2).
In addition, it is confirmed by the Example mentioned later that reaction shown by said Formula (2) will be accelerated | stimulated when plasma gas is injected.

It is the tin oxide present near the surface of the molten tin that adheres to the lower surface of the float glass and causes a tin defect.
According to the embodiment of the present invention, since the reduction of tin oxide present in the vicinity of the surface of the molten tin 20 is promoted by injecting the plasma gas to the molten metal exposed portion 22, the float of good quality with few tin defects. Can produce glass.

The embodiment of the present invention is the distance in the width direction of the molten metal exposed portion 22 (the distance (length) of the molten metal exposed portion 22 along the width direction of the glass ribbon G). When the distance to the inner wall is W (mm), injecting the plasma gas at a distance of 0.3 W or more in the width direction exhibits the function of promoting the reduction of tin oxide present in the vicinity of the surface of molten tin 20 It is preferable to do. The width direction distance for injecting the plasma gas is equal to the width direction distance W1 of the plasma gas injection unit 31. The widthwise distance W1 is more preferably 0.5 W or more, further preferably 0.7 W or more. However, if the widthwise distance W1 is equal to or more than W, the plasma jet device 30 is present above the glass ribbon G. Therefore, foreign matter attached to the plasma jet device 30 falls on the glass ribbon G to cause a defect. There is a fear. Therefore, the widthwise distance W1 is preferably W or less.
In FIGS. 1 and 2, a part of the plasma injection device 30 is located outside the molten metal tank 10 in order to connect with external equipment such as a power supply.

As shown in FIG. 1, the widthwise distance W of the molten metal exposed portion 22 differs depending on the position of the molten metal exposed portion 22 in the molten metal tank 10, specifically, the position in the flow direction of the glass ribbon G.
The widthwise distance W of the molten metal exposed portion 22 also differs depending on the size and shape of the molten metal tank 10.
The widthwise distance W of the molten metal exposed portion 22 at the portion where the plasma injection device 30 is disposed is preferably 100 to 600 mm, and more preferably 200 to 500 mm. The reason is as described below.
When the widthwise distance W is 100 mm or more, even if the glass ribbon G fluctuates in the widthwise direction, it is possible to prevent the occurrence of a trouble in which the glass ribbon G contacts and adheres to the side wall of the molten metal tank 10. Moreover, if the width direction distance W is 600 mm or less, the glass ribbon G having a wide width can be efficiently formed without increasing the size in the width direction of the molten metal tank 10.

Embodiments of the present invention preferably inject plasma gas at a flow distance of 10 to 400 mm. The flow direction distance for injecting the plasma gas coincides with the flow direction distance L1 of the plasma gas injection unit 31. The flow direction distance L1 is more preferably 50 to 400 mm. Here, “the flow direction distance L1 of the plasma gas injection unit 31” means the distance (length) of the plasma gas injection unit 31 along the flow direction of the glass ribbon.
In the embodiment of the present invention, it is preferable to inject the plasma gas at a distance of 5 to 30 mm above the molten metal exposed portion 22 in the vertical direction. The vertical distance corresponds to the vertical distance between the plasma gas injection unit 31 and the molten metal exposed unit 22. As the vertical distance increases, the above-described effects of the plasma gas injection decrease. However, if the vertical distance is too small, the plasma gas injection unit 31 may come into contact with the molten metal exposed portion 22 and the glass ribbon G present on the molten tin 20. The vertical distance is more preferably 5 to 20 mm.
In FIGS. 1 and 2, one plasma injection device 30 is disposed on each of the left and right sides of the glass ribbon G. When arranging a plurality of plasma injection devices 30 along the flow direction of molten metal exposed portion 22, the distance between the plurality of plasma injection devices is not particularly limited, and the number of arranged plasma injection devices and the glass in the plasma injection device It may be appropriately selected according to the flow direction distance of the ribbon G.

Here, as apparent from FIG. 4A, the range in which the plasma generating apparatus 40a injects the plasma gas is determined by the size of the gas discharge part 43, and the size of the gas discharge part 43 substantially matches the distance between the electrodes 44. Do. The distance between the electrodes is preferably 1 to 600 mm. The longitudinal distance of the housing 41 is preferably 5 to 600 mm. Further, it is preferable that the distance in the paper surface depth direction of the housing 41 in FIGS. 4A and 5A is 5 to 400 mm.

As described above, the plasma gas preferably contains an inert gas and / or a reducing gas in order to promote the reaction represented by the formula (2) by the injection of the plasma gas. The gas type contained in the plasma gas is the same as the gas introduced from the gas introduction unit 42.
The inert gas, He, Ne, Ar, N 2 is illustrated. The reducing gas, CO, CO ₂ and, H ₂ containing H in the _{molecule, H 2 O, NH 3,} CH 4, C 2 H 2, C 2 H 4, C 2 H 6 can be exemplified. Among them, plasma gas, He, Ne, Ar, from _{N 2, CO, CO 2,} H 2, H 2 O, NH 3, CH 4, C 2 H 2, C 2 H 4 and C ₂ H ₆ It is preferable to contain at least one selected from the group consisting of
Therefore, the plasma gas may contain only an inert gas such as He, Ne, Ar, N ₂ . Among these, Ar and N ₂ are preferable in terms of cost. Only one of Ar and N ₂ may be used, or two or more of them may be used in combination.
As the reducing gas, H ₂ is preferable because the cost is low and the amount of reactive species is large.

More preferably, the plasma gas contains H ₂ . In this case, only H ₂ may be contained, and an inert gas may be contained together with H ₂ . When an inert gas is contained together with H ₂ , for example, a gas containing H ₂ and Ar, a gas containing H ₂ and N ₂ , a gas containing H ₂ , Ar and N ₂ can be used.

As in the case where the plasma gas contains H ₂ , when a gas species that positively generates a hydrogen radical which is a reactive species is selected, the plasma gas is jetted and reaches the molten metal exposed portion 22 The hydrogen radical density in the atmosphere is preferably 1 × 10 ¹¹ / cm ³ or more, more preferably 1 × 10 ¹² / cm ³ or more, in terms of room temperature. When the hydrogen radical density is 1 × 10 ¹¹ / cm ³ or more, reduction of tin oxide present in the vicinity of the surface of the molten tin 20 is promoted even at the lowest temperature part of the atmosphere in the float bath 100.
When the plasma gas contains only an inert gas, hydrogen in the atmosphere in the float bath 100 is trapped between the plasma gas injection portion 31 and the molten metal exposed portion 22 to be radicalized. The hydrogen radical density is about 1 × 10 ¹¹ / cm ³ .
The hydrogen radical density was measured by vacuum ultraviolet spectroscopy. A microhollow cathode plasma light source having a known spectrum was used as a light source, and a monochromator with a photomultiplier was used as a detector. Using a light source on the front side of the plasma generator 40a, 40b shown in FIGS. 4 (a) and 5 (a), a position 0 to 10 mm below the paper from the longitudinal center of the plasma gas injection site. The light was made incident, and the absorption intensity was measured by a detector located on the back side of the plasma generating devices 40a and 40b as viewed in the drawing. From this, the hydrogen radical density was calculated from known spectral information.

In the embodiment of the present invention, it is preferable to inject the plasma gas at a linear velocity (in terms of room temperature) of 0.1 to 200 m / s, regardless of which gas type is contained. If the linear velocity is 0.1 m / s or more, hydrogen radicals can be sufficiently transported to the molten metal exposed portion 22. In addition, when the linear velocity is 200 m / s or less, fluctuation of the liquid level of the molten metal exposed portion 22 can be suppressed.

In the case of containing any gas species, it is preferable that the electron density of plasma gas in the plasma conversion region P is 1 × 10 ¹³ / cm ³ or more in terms of room temperature.
The electron density of the plasma gas was calculated by measuring the Stark spread of the Balmer beta ray of hydrogen in emission analysis of plasma at room temperature. The emission of plasma gas was detected by a multi-channel spectroscope equipped with a charge coupled device array on the lower side of the surface of the plasma generating devices 40a and 40b shown in FIGS. 4 (a) and 5 (a). The density of the plasma gas was calculated from the full width at half maximum due to the Stark spread of the obtained Balmer beta ray of hydrogen.

In FIG. 1, the plasma injection device 30 is disposed in the narrow region Z3 of the molten metal exposed portion 22 on the downstream side of the flow direction of the glass ribbon G. However, the present invention is not limited thereto. The plasma injection device may be disposed in the wide area Z1 or the intermediate area Z2 of
However, when the plasma injection device is disposed on the upstream side in the flow direction of the glass ribbon, molten tin reduced from tin oxide may be oxidized again. Therefore, it is preferable to dispose the plasma injection device 30 in the narrow region Z3 on the downstream side of the flow direction of the glass ribbon G.

In the molten metal exposed portion 22 in the molten metal tank 10, it is preferable that the oxygen potential after the plasma gas injection is not more than half the oxygen potential before the plasma gas injection. This is because the oxygen potential in the molten metal decreases as the reduction of tin oxide by the plasma gas is promoted.
The oxygen potential can be measured using a zirconia-based oxygen sensor. Specifically, the measurement electrode made of metal, the reference electrode whose oxygen potential is always constant, and the sensor are submerged in the molten metal tank 10, and the voltage difference between the electrodes generated due to the difference in oxygen potential The oxygen potential can be determined. In addition, the sensor uses the stabilized zirconia which expresses oxygen ion conductivity under high temperature.

When focusing on the temperature of the molten metal to which the plasma gas is injected, the temperature of the molten metal is preferably 900 ° C. or less. Although it also depends on the composition of the glass produced by the float method, it is because the molten metal temperature in the narrow zone Z3 is usually 900 ° C. or less. From the composition of the glass to be produced, it is preferable to appropriately select the temperature of the molten metal to which the plasma gas is injected in the temperature range of 900 ° C. or less. The lower limit of the temperature of the molten metal to which the plasma gas is injected is not particularly limited, but the temperature of the molten metal is usually 500 ° C. or higher in order to inject the plasma gas to the molten metal exposed portion 22 in the molten metal tank 10. is there.

Embodiments of the present invention are broadly applicable to sheet glass produced by the float process. The glass composition is also not particularly limited, and it can be applied to a wide range of glasses such as soda lime silicate glass, aluminosilicate glass, borosilicate glass, alkali-free glass and the like.

The thickness of the glass sheet produced according to the embodiment of the present invention is not particularly limited, but preferably 0.1 to 2.0 mm.

Hereinafter, the present invention will be further described using examples.
In the example, the reduction rate of the SnO ₂ film when the plasma gas was jetted to the SnO ₂ film formed by sputtering on the glass plate was evaluated according to the following procedure.
A 20 mm square quartz glass plate was used as the glass plate. A 500 nm thick SnO ₂ film was formed by sputtering over the entire surface on one main surface of the glass plate. Thereafter, the center φ5 mm of the SnO ₂ film was masked, the other SnO ₂ films were removed by the etching solution, and a sample in which the SnO ₂ film remained only in the masking portion was produced. This is to ensure that the plasma gas is uniformly processed over the SnO ₂ film, which is an analytical convenience.
While the glass plate was heated to 500 ° C., 625 ° C. or 750 ° C., a plasma gas was injected from the plasma generator 40 _b shown in FIG. 5 to the SnO ₂ film.
The plasma generator 40b shown in FIG. 5A has a micro hollow cathode discharge type, the distance between the electrodes 44 is 20 mm, and the distance from the lower surface of the plasma conversion region P to the first discharge part 43 is 6 mm. . The height of the second discharge portion 45 is 1 mm, and the diameter of the circular hole having a cross-sectional shape formed in the second discharge portion 45 is 0.5 mm, and the total cross-sectional area of the holes occupies the entire lower surface of the plasma generator 40b The ratio of is 0.55%.
A mixed gas (H ₂ 8 vol%) of Ar and H ₂ was supplied at a linear velocity of 12.1 m / s as a gas to be plasmatized from the gas introduction unit 42 with the pressure of the plasma conversion region P being atmospheric pressure.
A voltage of 9 kV was applied between the electrodes 44 from a high frequency power supply with a frequency of 20 kHz.
The distance between the plasma gas injection site (lower surface of the second discharge unit 45) and the injection site (SnO ₂ film) was 5 mm.
The processing time (plasma gas injection time) was 10 sec to 90 sec.

After the 17.5% hydrochloric acid treatment of the SnO ₂ film after the plasma gas injection, fluorescent X-ray analysis (XRF) was performed. XRF was also performed on the SnO ₂ film before the plasma gas injection.
The converted residual film thickness l (nm) was calculated from Tin-count obtained by XRF using the following equation.
l [nm] = 500 [nm] x Tin-count after plasma gas injection (after hydrochloric acid treatment) / Tin-count before plasma gas injection
The converted residual film thickness l was plotted with respect to the processing time (plasma gas injection time), and the slope was taken as the SnO ₂ film reduction rate.

As a comparative example, in a state where the glass plate was heated to 500 ° C., 625 ° C. or 750 ° C., XRF was carried out after the hydrochloric acid treatment also for the sample held for the above processing time without injecting the plasma gas to the SnO ₂ film.

The results are shown in FIGS. FIG. 6 is a view showing the SnO ₂ reduction rates of an example (with plasma) and a comparative example (without plasma) at a glass plate temperature of 500 ° C. FIG. 7 is a view showing the SnO ₂ reduction rates of the example (with plasma) and the comparative example (without plasma) having a glass plate temperature of 625 ° C. FIG. 8 is a view showing the SnO ₂ reduction rates of an example (with plasma) and a comparative example (without plasma) at a glass plate temperature of 750 ° C. From these results, it can be seen that the injection rate of plasma gas improved the SnO ₂ reduction rate. In addition, the SnO ₂ reduction rate has a glass plate temperature dependency, and in the temperature range implemented this time, the higher the temperature, the larger the SnO ₂ reduction rate tends to be.

The distance between the plasma gas injection site (the lower surface of the second discharge part 45) and the injection site (SnO ₂ film) is set to 5 mm, 10 mm and 15 mm as a glass plate temperature of 500 ° C. and processing time (plasma gas injection time) 60 sec. Carried out in FIG. 9 is a diagram showing the distance dependency between the plasma gas injection site and the injection site of the SnO ₂ reduction rate based on this result. From FIG. 9, the SnO ₂ reduction rate has a negative correlation with the distance between the plasma gas injection site and the injection site, and the SnO ₂ reduction speed decreases as the distance between the plasma gas injection site and the injection site increases. I know what to do. This is considered to be because the amount of deactivation of the hydrogen radical which is a reactive species increases as the distance increases.

A mixed gas of Ar and H ₂ (H ₂ 8 vol%) of 4.04 m / s, 12.1 m / s, 24.3 m / s 3 with a glass plate temperature of 500 ° C. and a treatment time (plasma gas injection time) of 60 sec. It supplied and implemented from the gas introduction part 42 at a linear velocity of the street. FIG. 10 shows the linear velocity dependency of the plasma gas of the SnO ₂ reduction rate. It can be seen from FIG. 10 that the SnO ₂ reduction rate has a positive correlation with the linear velocity of the plasma gas, and the larger the linear velocity of the plasma gas, the better the SnO ₂ reduction rate. This is considered to be because, as the linear velocity of the plasma gas increases, the amount of hydrogen radicals that are reactive species is transported to the object without being deactivated.

FIG. 11 is a diagram showing the difference in the SnO ₂ reduction rate depending on the presence or absence of the second discharge part of the plasma generator. Assuming that the linear velocity is 4.04 m / s, the distance between the plasma gas injection site and the injection site (SnO ₂ film) is 5 mm, and the processing time (plasma gas injection time) is 60 sec, the glass plate temperature is 500 ° C, 625 ° C, 750 ° C Carried out in three ways. The cross-sectional shape of the gas discharge part 43 of the plasma generator 40a shown in FIG. 4 was a linear rectangle having a distance (long side) of 20 mm and a short side of 0.3 mm in the longitudinal direction of the electrode 44. Further, in the cross-sectional shape of the second discharge part 45 of the plasma generator 40b shown in FIG. 5, 21 circles are arranged along the longitudinal direction of the electrode 44 with a diameter of 0.5 mm and a pitch of 0.5 mm. did. From FIG. 11, it can be seen that the reduction rate is faster in the plasma generator 40a than in the plasma generator 40b. This is considered to be because the area of the wall in contact with the plasma gas is larger in the plasma generating apparatus 40b than in the plasma generating apparatus 40a, and thus the amount of reactive species captured and inactivated is increased.

FIG. 12 is a diagram showing the temporal transition of the oxygen potential of molten tin before and after the injection of plasma gas. 300 g of tin was placed in a 25 mm deep alumina crucible and heated to 750 ° C. to form molten tin. The oxygen potential of molten tin was measured by a zirconia-type oxygen sensor before and after the mixed gas of Ar and H ₂ ( ₄ vol% of H ₂ ) made into plasma was jetted to the molten tin using the plasma generator 40 a shown in FIG. 4. The distance from the molten tin surface to the gas discharge part 43 of the plasma generator 40a was 5 mm, and the measurement part of the zirconia type oxygen sensor was installed at a depth of 20 mm from the molten tin surface. The arrows in FIG. 12 indicate the time zone in which the mixed gas of Ar and H ₂ is plasmatized, and in this time zone, the absolute value of the slope is larger than the time zone in which the plasmatization is not conducted. This indicates that the decay time of the oxygen potential is faster in the plasmad time zone.
Further, in the vicinity of 300 minutes in FIG. 12, a mixed gas of Ar and H _2, which was not plasma is that the common logarithm of the oxygen potential has converged in the vicinity of -23, plasma was Ar and H ₂ In the mixed gas, the common logarithm value of the oxygen potential converged to around -24.3 at around 380 minutes. This is considered to be a result of the equilibrium of the oxygen potential of molten tin shifted to a smaller value by plasmatization. The equilibrium value is considered to change depending on the distance between the molten tin and the plasma generator 40a, the concentration of plasma gas, the linear velocity, and the like.

Although the invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention.
This application is based on Japanese Patent Application No. 2017-214508 filed on Nov. 7, 2017, the contents of which are incorporated herein by reference.

10: Molten metal tank 12: Roof 20: Molten tin 22: Molten metal exposed part 30: Plasma injection device 31: Plasma gas injection part 32: Support part 40a, 40b: Plasma generator 41: Housing 42: Gas introduction part 43 : Gas discharge unit (first discharge unit)
44: Electrode 45: Second discharge part G: Glass ribbon P: Plasmaized area

Claims (13)

A method of producing float glass, comprising forming molten glass obtained by melting a glass raw material into a glass ribbon on molten metal in a float bath, and gradually cooling the obtained glass ribbon to obtain a sheet glass,
A method of manufacturing float glass, comprising: injecting a plasma gas to a molten metal exposed portion exposed to an atmosphere in the float bath. 2. The float glass according to claim 1, wherein the plasma gas is injected to the molten metal exposed portion at a width direction distance of 0.3 W or more, where W (mm) is the width direction distance of the molten metal exposed portion. Production method. The method for producing float glass according to claim 1 or 2, wherein the plasma gas is jetted to the molten metal exposed portion at a flow direction distance of 10 to 400 mm. The float glass according to any one of claims 1 to 3, wherein the plasma gas is injected to the molten metal exposed portion at a distance of 5 to 30 mm in a vertical direction upward from the molten metal exposed portion. Production method. The plasma gas, He, Ne, Ar, N 2, CO, CO 2, H 2, H 2 O, from the group consisting of _{NH 3, CH 4, C 2} H 2, C 2 H 4 and C ₂ H ₆ The method for producing a float glass according to any one of claims 1 to 4, which contains at least one selected. The method for producing float glass according to claim 5, wherein the hydrogen radical density in the atmosphere until the plasma gas is jetted and reaches the molten metal exposed portion is 1 × 10 ¹¹ / cm ³ or more. The method for producing float glass according to claim 5 or 6, wherein the plasma gas is injected onto the molten metal exposed portion at a linear velocity of 0.1 to 200 m / s. The plasma gas is injected from a plasma injection device provided opposite to the upper side of the molten metal exposed portion,
The plasma injection apparatus includes a plasma gas injection unit that injects the plasma gas.
The plasma gas injection unit includes a plurality of plasma generators.
The float glass according to any one of claims 1 to 7, wherein an electron density of the plasma gas in a plasma formation region for plasmatizing a gas introduced into the plasma generator is 1 × 10 ¹³ / cm ³ or more. Production method. 9. The molten metal exposed portion according to any one of claims 1 to 8, wherein the oxygen potential of the molten metal after the plasma gas injection is not more than half the oxygen potential of the molten metal before the plasma gas injection. The manufacturing method of the float glass as described. The method for producing float glass according to any one of claims 1 to 9, wherein the temperature of the molten metal to which the plasma gas is injected is 900 属 C or less. A float glass manufacturing apparatus, wherein molten glass obtained by melting a glass material is formed into a glass ribbon on molten metal in a float bath, and the obtained glass ribbon is gradually cooled to obtain a sheet glass,
A plasma injection device is disposed above the molten metal exposed portion exposed to the atmosphere in the float bath,
The plasma injection apparatus includes a plasma gas injection unit, and a support unit that supports the plasma gas injection unit.
The apparatus for manufacturing float glass, wherein the plasma gas injection unit injects plasma gas to the molten metal exposed portion. The plasma gas injection unit includes a plurality of plasma generators.
The apparatus for manufacturing float glass according to claim 11, wherein the plasma generating apparatus is arranged such that a longitudinal direction of the plasma generating apparatus and a flow direction of the glass ribbon coincide with each other. The float glass manufacturing apparatus according to claim 12, wherein the cross-sectional shape of the gas discharge part of the plasma generator is rectangular.

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