CN111315693B - Method for manufacturing float glass and device for manufacturing float glass - Google Patents

Abstract

The present invention relates to a method for producing float glass, characterized in that a molten glass obtained by melting a glass raw material is formed into a glass ribbon on molten tin in a float bath, and the obtained glass ribbon is slowly cooled to obtain a glass plate.

Description

Manufacturing method of float glass and manufacturing apparatus of float glass

technical field

The present invention relates to a float glass manufacturing method and a float glass manufacturing apparatus that reduce tin defects.

Background technique

In the manufacture of float glass, it is important to reduce the dissolution of molten tin by oxygen in the float bath. One of the reasons for this is that tin oxide, which is produced by dissolving oxygen in molten tin, adheres to the lower surface of the float glass, thereby causing tin defects.

In the past, in order to prevent the contact between molten tin and oxygen in the float bath, the float bath was closed as much as possible, and high-purity nitrogen was blown as a protective atmosphere to prevent the intrusion of air, and at the same time, hydrogen was blown to remove Oxygen in invading traces of air. In addition, in order to prevent the intrusion of oxygen in the air, the pressure of the protective atmosphere gas in the float bath is set to be slightly higher than the atmospheric pressure outside the float bath.

In recent years, in order to improve the manufacturing yield, it is required to further reduce tin defects. In order to meet this requirement, a method of directly removing tin oxide itself in molten tin is required.

Therefore, Patent Document 1 proposes a method in which a part of the molten tin in the tin bath is taken out from the tin bath, the tin oxide in the taken out molten tin is reacted and removed, and then returned to the tin bath.

prior art literature

Patent Literature

Patent Document 1: Japanese Patent No. 4281141.

SUMMARY OF THE INVENTION

However, in the method described in Patent Document 1, it is necessary to provide a circulation system for circulating molten tin outside the tin bath, and in order to remove tin oxide in the molten tin, it is necessary to cool the molten tin to a temperature lower than the minimum temperature in the tin bath , heat the molten tin again before returning to the tin bath. Therefore, although the method described in Patent Document 1 can reduce tin defects, there are problems in that the equipment configuration and manufacturing conditions are complicated, and the equipment investment cost and operating cost are high.

This invention was made in view of the said subject, and an object is to provide the manufacturing method and the manufacturing apparatus of a float glass which obtain a glass plate of good quality by simple manufacturing conditions.

In order to solve the above-mentioned problems, the present invention provides a method for producing a float glass, wherein the glass obtained by slowly cooling a molten glass obtained by melting a glass raw material is formed into a glass ribbon on a molten metal in a float bath, and then gradually cooled. The manufacturing method of the float glass with which the glass plate was obtained, and a plasma gas is sprayed to the molten metal exposure part exposed in the atmosphere in the said float bath.

In the manufacturing method of the float glass of this invention, it is preferable to spray the said plasma gas to the molten metal exposure part with the width direction distance 0.3W or more, when the width direction distance of the said molten metal exposure part is W (mm).

In the manufacturing method of the float glass of this invention, it is preferable to spray the said plasma gas with respect to a molten metal exposure part at a flow direction distance of 10-400 mm.

In the manufacturing method of the float glass of this invention, it is preferable to spray the said plasma gas to the molten metal exposed part so that the vertical direction distance may be separated from the said molten metal exposed part upwards by 5-30 mm.

In the method for producing float glass of the present invention, the plasma gas preferably contains a material selected from the group consisting of He, Ne, Ar, N ₂ , CO, CO ₂ , H ₂ , H ₂ O, NH ₃ , CH ₄ , and C ₂ H ₂ , at least one of C ₂ H ₄ and C ₂ H ₆ .

In the manufacturing method of the float glass of this invention, it is preferable that the said plasma gas is sprayed, and the hydrogen radical density in the atmosphere until reaching the said molten metal exposure part is 1*10<^11>/cm< ³ > or more.

In the manufacturing method of the float glass of this invention, it is preferable to spray a plasma gas to a molten metal exposure part at a linear velocity of 0.1-200 m/s.

In the manufacturing method of float glass of the present invention, preferably,

The plasma gas is sprayed from a plasma spray device provided to face the upper side of the molten metal exposure portion,

The above-mentioned plasma spraying apparatus includes a plasma gas spraying unit that sprays plasma gas,

The above-mentioned plasma gas injection part includes a plurality of plasma generating devices,

The electron density of the plasma gas in the plasmaization region where the gas introduced into the plasma generator is plasmatized is 1×10 ¹³ /cm ³ or more.

In the float glass manufacturing method of this invention, it is preferable that the oxygen potential of the said molten metal after plasma gas injection in the said molten metal exposure part is 1/2 or less of the oxygen potential of the said molten metal before plasma gas injection.

In the manufacturing method of the float glass of this invention, it is preferable that the temperature of the said molten metal to which plasma gas is sprayed is 900 degrees C or less.

In addition, the present invention provides a float glass manufacturing apparatus obtained by forming molten glass obtained by melting glass raw materials on molten metal in a float bath into a glass ribbon, and gradually cooling the obtained glass ribbon. The manufacturing apparatus of the float glass of the glass plate is arranged above the molten metal exposure part exposed in the atmosphere in the said float bath, and the plasma spraying apparatus is arrange|positioned, The said plasma spraying apparatus is provided with the plasma gas spraying part, and supports this The support part of the plasma gas injection part, and the plasma gas injection part injects the plasma gas to the molten metal exposure part.

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 said plasma generator is arrange|positioned so that the longitudinal direction of this plasma generator may correspond to the flow direction of the said glass ribbon.

It is preferable that the cross-sectional shape of the gas discharge part of the said plasma generator of the manufacturing apparatus of the float glass of this invention is a rectangle.

ADVANTAGE OF THE INVENTION According to this invention, the float glass with good quality can be manufactured under simple manufacturing conditions.

Description of drawings

FIG. 1 is a plan view showing a configuration example of a lower structure of a float bath.

FIG. 2 is a partial cross-sectional view taken along the line II in FIG. 1 .

FIGS. 3( a ) and 3 ( b ) are schematic diagrams of main parts of the plasma ejection apparatus, FIG. 3( a ) is a schematic diagram viewed from a plane direction, and FIG. 3( b ) is a cross section of FIG. 2 Schematic view of the obtained direction.

FIG. 4( a ) is a cross-sectional view showing a configuration example of a 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 ).

6 is a graph showing SnO ₂ reduction rates of Examples and Comparative Examples at a glass plate temperature of 500°C.

FIG. 7 is a graph showing the SnO ₂ reduction rate of Examples and Comparative Examples at a glass plate temperature of 625°C.

FIG. 8 is a graph showing the SnO ₂ reduction rate of Examples and Comparative Examples at a glass plate temperature of 750°C.

9 is a graph showing the distance dependence of the SnO ₂ reduction rate between the plasma gas injection site and the sprayed site.

FIG. 10 is a graph showing the linear velocity dependence of the SnO ₂ reduction rate of the plasma gas.

11 is a graph showing a difference in SnO ₂ reduction rate depending on whether the plasma generator has a second discharge portion or not.

FIG. 12 is a graph showing the temporal transition of the oxygen potential of molten tin before and after the injection of the plasma gas.

Detailed ways

Hereinafter, the manufacturing method of the float glass and the manufacturing apparatus of the float glass which are one Embodiment of this invention are demonstrated, referring drawings.

In the present invention, molten glass obtained by melting glass raw materials is formed into a glass ribbon on molten metal in a float bath, and the obtained glass ribbon is gradually cooled to obtain a glass plate.

FIG. 1 is a plan view showing a configuration example of a lower structure of a float bath, and FIG. 2 is a partial cross-sectional view taken along the line II in FIG. 1 .

The float bath 100 shown in the figure is composed of a molten metal tank 10 in which molten tin 20 is accommodated, a ceiling 12 arranged above the molten metal tank 10 , and the like.

In addition, the metal accommodated in the molten metal tank 10 may be a tin alloy, a metal other than tin, or its alloy. Tin alloys are, for example, alloys of tin and copper. In addition, the metal other than tin is, for example, bismuth. In addition, the alloy of metals other than tin is, for example, an alloy of bismuth and copper.

On the molten tin 20 of the molten metal tank 10, the molten glass obtained by melting glass raw material is continuously supplied. The molten glass is made to flow on the molten tin 20 of the molten metal tank 10, and it shape|molds into the ribbon-shaped glass ribbon G. The glass ribbon G moves in the direction of the arrow in the figure. Hereinafter, in this specification, the arrow direction in a figure is called the flow direction of the glass ribbon G, and the direction orthogonal to the arrow direction is called the width direction of the glass ribbon G. In addition, in this specification, "flow direction" and "width direction" correspond to "the flow direction of glass ribbon G" and "the width direction of glass ribbon G", respectively.

The molten metal tank 10 includes a wide region Z1 having a wide width, a middle region Z2 having a narrow width, and a narrow region Z3 having a narrow width in this order from the upstream side in the flow direction of the glass ribbon G. Between the glass ribbon G and the side wall of the molten metal tank 10 (hereinafter, it may be described as the left and right sides of the glass ribbon G), there is a molten metal exposed portion 22 that exposes the molten tin 20 in the atmosphere in the float bath 100 . . The plasma spray apparatus 30 is arrange|positioned above the molten metal exposure part 22 which exists on the left and right sides of the glass ribbon G of the narrow area Z3.

The plasma injection device 30 includes a plasma gas injection part 31 and a support part 32 that supports the plasma gas injection part 31 . The plasma gas injection part 31 is provided so as to protrude below the support part 32 . The plasma gas injection unit 31 is composed of a plurality of plasma generators 40 a to be described later, and injects plasma-ized gas (hereinafter referred to as plasma gas) toward the molten metal exposure portion 22 . The inside of the support part 32 is provided with the duct for supplying the gas to be plasmatized to the plasma generator 40a, and the wiring for applying a voltage to the electrode of the plasma generator 40a.

The plasma gas injection part 31 may be provided inside the support part 32 . In this case, the support portion 32 must have a height for accommodating at least the plasma generator 40a.

FIG. 3 is a schematic diagram of a main part of the plasma spray apparatus, FIG. 3( a ) is a schematic diagram viewed from a plane direction, and FIG. 3( b ) is a schematic diagram viewed from a cross-sectional direction of FIG. 2 .

The plasma spray device 30 includes a plasma gas spray portion 31 and a support portion 32 . The plasma gas injection part 31 shown in FIG.3(a) consists of eight plasma generators 40a, and the width direction distance of the plasma gas injection part 31 is W1, and the flow direction distance is L1. Here, "the width direction distance of the plasma gas injection part 31" means the distance (length) of the plasma gas injection part 31 along the width direction of a glass ribbon. In addition, "the distance of the flow direction of the plasma gas injection part 31" means the distance (length) of the plasma gas injection part 31 along the flow direction of a glass ribbon.

The plasma generator 40a may be arranged so that the longitudinal direction of the plasma generator 40a matches the flow direction of the glass ribbon. In FIG.3(a), the plasma generator 40a is arrange|positioned so that it may be arranged in two rows along the flow direction of the glass ribbon, and may be arranged in four rows along the width direction of the glass ribbon.

The plasma generator 40a is preferably arranged in 1 to 6 rows along the flow direction of the glass ribbon, and 1 to 15 rows along the width direction of the glass ribbon. Moreover, the plasma generator 40a may be arrange|positioned so that the longitudinal direction of the plasma apparatus 40a may correspond to the width direction of a glass ribbon. At this time, the plasma generator 40a may be arranged in 1 to 15 rows along the flow direction of the glass ribbon, and 1 to 6 rows along the width direction of the glass ribbon.

A gap may be provided along the flow direction or the width direction of the glass ribbon between adjacent plasma generators 40a. In order to spray the plasma gas uniformly along the flow direction or the width direction of the glass ribbon, the gap is preferably small.

The plasma gas injection part 31 may replace all or a part of the plasma generator 40a with the plasma generator 40b mentioned later.

FIG. 4( a ) is a cross-sectional view showing a configuration example of the plasma generator 40 a , and FIG. 4( b ) is a partial cross-sectional view taken along the line II-II in FIG. 4( a ). In the plasma generator 40a shown in FIG.4(a), the gas introduction part 42 which introduce|transduces the gas for plasmaization is provided in the upper part of the housing|casing 41 which consists of sintered bodies, such as alumina. Below the gas introduction part 42, there is a plasmaization region P that plasmaizes the introduced gas. In the plasmaization region P, two electrodes 44 are inserted at intervals from the side surface of the frame body 41 , and a predetermined voltage is applied between the electrodes 44 while continuously introducing a gas from the gas introduction portion 42 to generate a discharge. The introduced gas becomes plasma. The plasma gas (plasma gas) is discharged from the gas discharge part 43 provided in the lower part of the casing 41 .

As shown in FIG. 4( b ), the cross-sectional shape of the gas discharge portion 43 is a rectangle whose long side is the longitudinal direction of the electrode 44 , and is preferably a linear rectangle (slit) whose short side is particularly short. Thereby, since the reactive species of the plasma gas discharged from the gas discharge part 43 increases, 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 40b shown in FIG.5(a), the 2nd discharge part 45 is provided in the lower side of the gas discharge part (1st discharge part) 43. In the second discharge part 45 , a plurality of holes are arranged in a straight line, and radicals of the same density can be ejected along the longitudinal direction of the electrode 44 . As shown in FIG.5(b), the cross-sectional shape of the hole provided in the 2nd discharge part 45 is circular, and may be polygonal, such as an ellipse, a triangle, and a quadrangle. As a result, the discharge phenomenon of the plasma gas to the object to be processed can be suppressed.

In the plasma generator 40b shown in FIG.5(b), it is preferable that the ratio of the total cross-sectional area which a hole occupies in the whole lower surface of the plasma generator 40b is 0.01-5%.

The plasma generating devices 40a and 40b shown in Fig. 4(a) and Fig. 5(a) preferably have a hollow cathode discharge in the form of plasma discharge. Among them, but not limited to this, the plasma discharge form of the plasma generating device may be dielectric barrier discharge (DBD) and arc discharge. In addition, high-frequency induction discharge and microwave discharge without using electrodes may be used. In addition, discharge using a high-frequency power supply may be used.

In the embodiment of the present invention, the plasma gas is injected from the plasma gas injection unit 31 of the plasma injection apparatus 30 to the molten metal exposed portion 22 . Thereby, tin oxide existing in the vicinity of the surface of the molten tin 20 is reduced according to the mechanism described below.

As shown in the following formula (1), tin oxide SnO _x (0<x≦2 ).

Sn+O ₂ →SnO _x (1)

In the atmosphere in the float bath 100 , blowing hydrogen gas while blowing high-purity nitrogen gas is to reduce the tin oxide SnO _x in the molten tin 20 with the hydrogen in the atmosphere as shown in the following formula (2). Back to the metal Sn Sn.

SnO _x +H ₂ →Sn+H ₂ O(g) (2)

When the plasma gas is sprayed into the molten metal exposure 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 above formula (2).

In addition, it can be confirmed that the reaction represented by the above-mentioned formula (2) is accelerated when the plasma gas is injected from the examples described later.

It is tin oxide which exists in the vicinity of the surface of molten tin that adheres to the lower surface of float glass and produces a tin defect.

In the embodiment of the present invention, the reduction of tin oxide present in the vicinity of the surface of the molten tin 20 is promoted by spraying the plasma gas into the molten metal exposure portion 22 , so that it is possible to manufacture a high-quality float glass with few tin defects.

In the embodiment of the present invention, the width direction distance of the molten metal exposed portion 22 (which is the distance (length) of the molten metal exposed portion 22 along the width direction of the glass ribbon G, and the distance between the glass ribbon G and the molten metal tank 10 When the distance between the inner walls) is set to W (mm), spraying the plasma gas at a widthwise distance of 0.3W or more is preferable because it acts to promote the reduction of tin oxide existing near the surface of the molten tin 20 . The widthwise distance of the injected plasma gas corresponds to the widthwise distance W1 of the plasma gas injection part 31 . The width direction distance W1 is more preferably 0.5W or more, and further preferably 0.7W or more. However, since the plasma spray apparatus 30 exists above the glass ribbon G when the width direction distance W1 is W or more, there exists a possibility that the foreign material adhering to the plasma spray apparatus 30 may fall on the glass ribbon G and cause a defect. Therefore, it is preferable that the width direction distance W1 is W or less.

In FIGS. 1 and 2 , a part of the plasma spray device 30 is located outside the molten metal tank 10 for connection to external equipment such as a power source.

As shown in FIG. 1, the width direction distance W of the molten metal exposure part 22 differs depending on the position of the molten metal exposure part 22 in the molten metal tank 10, specifically the position in the flow direction of the glass ribbon G.

In addition, the width direction distance W of the molten metal exposure part 22 also differs according to the size and shape of the molten metal tank 10 .

The widthwise distance W of the molten metal exposed portion 22 at the location where the plasma spray device 30 is arranged is preferably 100 to 600 mm, and more preferably 200 to 500 mm. The reason is as follows.

If the width direction distance W is 100 mm or more, even if the glass ribbon G fluctuates in the width direction, the trouble that the glass ribbon G contacts and adheres to the side wall of the molten metal tank 10 can be prevented. Moreover, when the width direction distance W is 600 mm or less, the wide glass ribbon G can be shape|molded efficiently, without increasing the dimension of the width direction of the molten metal tank 10.

In the embodiment of the present invention, the plasma gas is preferably jetted at a distance in the flow direction of 10 to 400 mm. The flow direction distance of the injected plasma gas corresponds to the flow direction distance L1 of the plasma gas injection part 31 . The flow direction distance L1 is more preferably 50 to 400 mm. Here, "the distance L1 of the flow direction 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.

In the embodiment of the present invention, it is preferable to spray the plasma gas upward from the molten metal exposure portion 22 so that the distance in the vertical direction is separated by 5 to 30 mm. The vertical distance corresponds to the vertical distance between the plasma gas injection portion 31 and the molten metal exposure portion 22 . When the vertical distance is increased, the above-described effects by the injection of the plasma gas are reduced. However, when the distance in the vertical direction is too small, the plasma gas injection part 31 may come into contact with the molten metal exposure part 22 and the glass ribbon G existing on the molten tin 20 . The distance in the vertical direction is more preferably 5 to 20 mm.

In FIGS. 1 and 2 , one plasma spray device 30 is arranged on the left and right sides of the glass ribbon G, respectively. When a plurality of plasma spraying devices 30 are arranged along the flow direction of the molten metal exposure portion 22, the distance between the plurality of plasma spraying devices is not particularly limited, and depends on the number of plasma spraying devices to be arranged and the plasma The flow direction distance of the glass ribbon G in the bulk jet apparatus may be appropriately selected.

Here, as can be seen from FIG. 4( a ), the range in which the plasma generator 40 a sprays the plasma gas is determined by the size of the gas discharge portion 43 , which is substantially the same as the distance between the electrodes 44 . The distance between electrodes is preferably 1 to 600 mm. The distance in the longitudinal direction of the frame body 41 is preferably 5 to 600 mm. Moreover, it is preferable that the distance of the depth direction of the paper surface of the housing|casing 41 of FIG.4(a) and FIG.5(a) is 5-400 mm.

As described above, the plasma gas preferably contains an inert gas and/or a reducing gas because the reaction represented by the above formula (2) is promoted by the injection of the plasma gas. In addition, the kind of gas contained in the plasma gas is the same as that of the gas introduced from the gas introduction part 42 .

Examples of the inert gas include He, Ne, Ar, and N ₂ . Examples of the reducing gas include CO, CO ₂ , and H ₂ , H ₂ O, NH ₃ , CH ₄ , C ₂ H ₂ , C ₂ H ₄ , and C ₂ H ₆ containing H in the molecule. Among these, the plasma gas preferably contains a gas selected from the group consisting of He, Ne, Ar, 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 At least one of ₆ .

Therefore, the plasma gas may contain only inactive gases such as He, Ne, Ar, N ₂ . Among these, Ar and N ₂ are preferable from the viewpoint of cost. Of Ar and N ₂ , only one of them may be used, or two of them may be used in combination.

The reducing gas is preferably H ₂ from the viewpoints of low cost and a large amount of reactive species generated.

The plasma gas more preferably contains H ₂ . At this time, only H ₂ may be contained, or H ₂ and an inert gas may be contained. In the case of containing H ₂ and an inert gas, for example, a gas containing H ₂ and Ar, a gas containing H ₂ and N ₂ , or a gas containing H ₂ , Ar and N ₂ may be used.

When a gas species such as a hydrogen radical that actively generates a reactive species is selected, as in the case where the plasma gas contains H ₂ , the hydrogen radical density in the atmosphere until the plasma gas reaches the molten metal exposure portion 22 by spraying the plasma gas In terms of room temperature, it is preferably 1×10 ¹¹ /cm ³ or more, and more preferably 1×10 ¹² /cm ³ or more. When the hydrogen radical density is 1×10 ¹¹ /cm ³ or more, even in the lowest temperature portion of the atmosphere in the float bath 100 , reduction of tin oxide present near the surface of the molten tin 20 is promoted.

In addition, when the plasma gas contains only the inert gas, the hydrogen in the atmosphere in the float bath 100 is involved in the space between the plasma gas injection part 31 and the molten metal exposure part 22 and is radicalized, so The aforementioned hydrogen radical density is about 1×10 ¹¹ /cm ³ .

Hydrogen radical density was determined by vacuum ultraviolet spectrometry. As the light source, a micro-hollow plasma light source with a known spectrum was used, and as the detector, a monochromatic beam splitter with a photomultiplier tube was used. Using the light sources located on the near side of the paper surface of the plasma generators 40a and 40b shown in FIGS. 4( a ) and 5 ( a ), aiming down the paper surface from the center position in the longitudinal direction of the plasma gas injection site The light was incident at positions separated from the sides by 0 to 10 mm, and the absorption intensity was measured by the detectors located on the back side of the paper surface of the plasma generators 40a and 40b. Thus, the hydrogen radical density is calculated from the known spectral information.

In the embodiment of the present invention, it is preferable to spray the plasma gas at a linear velocity (in terms of room temperature) of 0.1 to 200 m/s when any gas species is contained. When 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, the fluctuation of the liquid level of the molten metal exposed portion 22 can be suppressed.

When any gas species is contained, the electron density of the plasma gas in the plasmatized region P is preferably 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 broadening of the Ballmer β line of hydrogen in the luminescence analysis of the plasma at room temperature. On the lower side of the paper surface of the plasma generating apparatuses 40a and 40b shown in FIG. 4( a ) and FIG. 5( a ), the luminescence of the plasma gas is detected by a multi-channel spectroscope with a charge-coupled device array. The density of the plasma gas was obtained by calculation from the half-value width caused by the obtained Stark broadening of the Ballmer β line of hydrogen.

In FIG. 1 , the plasma spray device 30 is arranged in the narrow region Z3 on the downstream side in the flow direction of the glass ribbon G in the molten metal exposure portion 22 , but the present invention is not limited to this, and the glass ribbon G may be located on the upstream side in the flow direction. The wide area Z1 and the middle area Z2 of the plasma spray device are configured.

However, when a plasma spray apparatus is arrange|positioned on the upstream side of the flow direction of a glass ribbon, there exists a possibility that molten tin reduced from tin oxide may be oxidized again. Therefore, it is preferable to arrange|position the plasma spray apparatus 30 in the narrow area Z3 of 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 1/2 or less of 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 is promoted with the plasma gas.

The oxygen potential can be measured using a zirconia type oxygen sensor. Specifically, a metal measuring electrode, a reference electrode whose oxygen potential is usually constant, and a sensor are immersed in the molten metal tank 10, and the oxygen potential can be obtained from the voltage difference between the electrodes due to the difference in oxygen potential. In addition, the stabilized zirconia which showed oxygen ion conductivity at high temperature was used for the sensor.

When focusing on the temperature of the molten metal to which the plasma gas is sprayed, the molten metal temperature is preferably 900° C. or lower. Although it also depends on the composition of the glass manufactured by the float method, the molten metal temperature of the said narrow area Z3 is 900 degrees C or less normally. According to 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 sprayed in the temperature range of 900° C. or lower. The lower limit of the temperature of the molten metal to which the plasma gas is sprayed is not particularly limited, but the temperature of the molten metal is usually 500° C. or higher in order to spray the plasma gas to the molten metal exposed portion 22 in the molten metal tank 10 .

Embodiment of this invention can be widely applied to the glass plate manufactured by the float method. The glass composition is not particularly limited, either, and it can be applied to glasses with a wide range of compositions, such as soda lime silicate glass, aluminosilicate glass, borosilicate glass, and alkali-free glass.

Although the thickness of the glass plate manufactured by embodiment of this invention is not specifically limited, Preferably it is 0.1-2.0 mm.

Example

Hereinafter, the present invention will be further described using examples.

In the examples, the SnO ₂ film reduction rate when the plasma gas was sprayed was evaluated by the procedure shown below with respect to the SnO ₂ film formed by sputtering on the glass plate.

As the glass plate, a 20 mm square quartz glass plate was used. A SnO ₂ film having a thickness of 500 nm was formed by sputtering on the entire one main surface of the glass plate. After that, a mask was applied to the center φ5 mm of the SnO ₂ film, and the other SnO ₂ films were removed with an etching solution to prepare a sample in which only the SnO ₂ film remained in the mask portion. This is for the plasma gas to uniformly process the entire SnO ₂ film for easy analysis.

In a state where the glass plate is heated to 500° C., 625° C., or 750° C., plasma gas is sprayed onto the SnO ₂ film from the plasma generating apparatus 40 b shown in FIG. 5 .

The discharge form of the plasma generator 40b shown in FIG. 5( a ) is a micro-hollow cathode discharge, the interval between the electrodes 44 is 20 mm, and the distance from the lower surface of the plasmaized region P to the first discharge portion 43 is 6mm. The height of the second discharge portion 45 is 1 mm, the diameter of the circular hole in the cross-sectional shape formed in the second discharge portion 45 is 0.5 mm, and the ratio of the total cross-sectional area occupied by the holes in the entire lower surface of the plasma generator 40 b is 0.55%.

Taking the pressure of the plasmaization region P as atmospheric pressure, a mixed gas of Ar and H ₂ (H ₂ 8 vol%) was supplied from the gas introduction part 42 at a linear velocity of 12.1 m/s as a gas for plasma formation.

A voltage of 9 kV was applied between the electrodes 44 from a high-frequency power supply having a frequency of 20 kHz.

The distance between the plasma gas injection site (the lower surface of the second discharge portion 45 ) and the sprayed site (SnO ₂ film) was 5 mm.

The treatment time (plasma gas injection time) is 10 sec to 90 sec.

After the SnO ₂ film after plasma gas injection was treated with 17.5% hydrochloric acid, fluorescence X-ray analysis (XRF) was performed. XRF was also performed on the SnO ₂ film before the plasma gas spraying was performed.

From the Tin-count obtained by XRF, the converted residual film thickness I (nm) was calculated using the following formula.

I[nm]=500[nm]×Tin-count after plasma gas injection (after hydrochloric acid treatment)/Tin-count before plasma gas injection

A curve was drawn for the converted residual film thickness I with respect to the processing time (plasma gas injection time), and the slope was used as the SnO ₂ film reduction rate.

As a comparative example, XRF was performed after also performing hydrochloric acid treatment on a sample in which a glass plate was heated to 500° C., 625° C., or 750° C. without spraying plasma gas to the SnO ₂ film for the above-mentioned treatment time.

The results are shown in FIGS. 6 to 11 . FIG. 6 is a graph showing the SnO ₂ reduction rate of Example (with plasma) and Comparative Example (without plasma) at a glass plate temperature of 500°C. FIG. 7 is a graph showing the SnO ₂ reduction rate of Example (with plasma) and Comparative Example (without plasma) at a glass plate temperature of 625°C. FIG. 8 is a graph showing the SnO ₂ reduction rate 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 reduction rate of SnO ₂ is increased by the injection of the plasma gas. In addition, the SnO ₂ reduction rate has a glass plate temperature dependence, and in the temperature range implemented this time, the SnO ₂ reduction rate tends to increase as the temperature increases.

The glass plate temperature was 500° C., the treatment time (plasma gas injection time) was 60 sec, and the distance between the plasma gas injection site (the lower surface of the second discharge part 45 ) and the injection site (SnO ₂ film) was set to 5 mm, The three values of 10mm and 15mm are implemented. FIG. 9 is a graph showing the distance dependence of the SnO ₂ reduction rate between the plasma gas injection site and the sprayed site based on the results. 9 , it can be seen that the _{SnO 2} reduction speed is negatively correlated with the distance between the plasma gas injection site and the sprayed site. It is considered that this is because the larger the distance, the greater the deactivation amount of the hydrogen radical which is the reactive species.

A glass plate temperature of 500° C. and a processing time (plasma gas injection time) of 60 sec were used, and Ar and H ₂ were supplied from the gas introduction part 42 at three linear speeds of 4.04 m/s, 12.1 m/s, and 24.3 m/s. Mixed gas (H ₂ 8 vol%) was carried out. FIG. 10 is a graph showing the linear velocity dependence of the SnO ₂ reduction rate of the plasma gas. According to FIG. 10 , it can be seen that the SnO ₂ reduction rate is positively correlated with the linear velocity of the plasma gas, and the SnO ₂ reduction rate increases as the linear velocity of the plasma gas increases. This is considered to be because the larger the linear velocity of the plasma gas, the larger the amount of the hydrogen radical that is the reactive species is transported to the object to be processed without deactivating the hydrogen radical.

11 is a graph showing a difference in SnO ₂ reduction rate depending on whether the plasma generator has a second discharge portion or not. The line speed was 4.04 m/s, the distance between the plasma gas injection part and the part to be injected (SnO ₂ film) was 5 mm, the processing time (plasma gas injection time) was 60 sec, and the glass plate temperature was 500° C., 625 3 values of °C and 750°C were implemented. The cross-sectional shape of the gas discharge part 43 of the plasma generator 40a shown in FIG. 4 is a linear rectangle with a distance (long side) of the electrode 44 in the longitudinal direction of 20 mm and a short side of 0.3 mm. In addition, the cross-sectional shape of the second discharge portion 45 of the plasma generator 40b shown in FIG. 5 is a shape in which 21 circles are lined up in the longitudinal direction of the electrode 44 with a diameter of 0.5 mm and a pitch of 0.5 mm. From FIG. 11 , it can be seen that the reduction rate of the plasma generator 40a is faster than the reduction rate of the plasma generator 40b. This is considered to be because the area of the wall in contact with the plasma gas of the plasma generator 40b is larger than that of the plasma generator 40a, and the amount of the reactive species captured and deactivated increases.

FIG. 12 is a graph showing the time transition of the oxygen potential of molten tin before and after plasma gas injection. 300 g of tin was placed in an alumina crucible with a depth of 25 mm, and heated to 750° C. to form molten tin. Before and after the mixed gas of Ar and H ₂ (H _{2 4} vol%) plasmatized using the plasma generator 40a shown in FIG. 4 was sprayed onto the molten tin, the oxygen content of the molten tin was measured using a zirconia type oxygen sensor. potential. The distance from the molten tin surface to the gas discharge part 43 of the plasma generator 40a was 5 mm, and the measuring part of the zirconia type oxygen sensor was provided at a depth of 20 mm from the molten tin surface. The arrows in FIG. 12 indicate the time region in which the mixed gas of Ar and H ₂ is plasmaized, and the absolute value of the slope is larger in this time region than in the time region without plasmaization. This means that the decay rate of the oxygen potential in the plasmaized time region is fast.

In addition, in the vicinity of 300 minutes in FIG. 12 , the common logarithmic value of the oxygen potential of the mixed gas of Ar and H ₂ that is not plasmaized converges to the vicinity of −23, whereas the plasma-transformed Ar and H ₂ gas has a For the mixed gas, the common logarithmic value of the oxygen potential converges around -24.3 around 380 minutes. This is considered to be the result that the equilibrium value of the oxygen potential of molten tin is shifted to a smaller value due to plasmaization. It is considered that this equilibrium value varies depending on the distance between the molten tin and the plasma generating device 40a, the concentration of the plasma gas, the linear velocity, and the like.

The present invention will be described in detail with reference to specific embodiments, but it is clear for those skilled in the art that various changes and corrections can be made without departing from the spirit and scope of the present invention.

This application is based on Japanese Patent Application No. 2017-214508 filed on November 7, 2017, the contents of which are incorporated herein by reference.

Symbol Description

10: Molten metal tank

12: Top

20: Molten Tin

22: Molten metal exposed part

30: Plasma spray device

31: Plasma gas injection part

32: Support part

40a, 40b: Plasma generation device

41: Frame

42: Gas introduction part

43: Gas discharge part (first discharge part)

44: Electrodes

45: Second discharge part

G: Glass Ribbon

P: Plasmaized region

Claims (12)

1. A method for producing float glass, characterized in that a molten glass obtained by melting a glass raw material is formed into a glass ribbon on a molten metal in a float bath, and the glass ribbon obtained is slowly cooled to obtain a glass plate,

and injecting a plasma gas into a molten metal exposed portion exposed in the atmosphere in the float bath so as to be separated by a distance of 5 to 30mm in a vertical direction from the molten metal exposed portion upward.

2. The method of manufacturing float glass according to claim 1, wherein the plasma gas is jetted to the molten metal exposed portion at a distance of 0.3W or more in the width direction when the distance in the width direction of the molten metal exposed portion is W mm.

3. A method of manufacturing float glass according to claim 1 or 2, wherein the plasma gas is jetted to the molten metal exposed portion at a distance of 10 to 400mm in a flow direction.

4. The method for manufacturing float glass according to any one of claims 1 to 3, wherein the plasma gas contains a gas selected from He, Ne, Ar, N₂、CO、CO₂、H₂、H₂O、NH₃、CH₄、C₂H₂、C₂H₄And C₂H₆At least one of (1).

5. The method of manufacturing float glass according to claim 4, wherein the plasma gas is ejected so that a hydrogen radical density in an atmosphere until reaching the molten metal exposed portion is 1 x 10¹¹/cm³The above.

6. A float glass production method according to claim 4 or 5, wherein the plasma gas is jetted at a linear velocity of 0.1 to 200m/s to the molten metal exposed portion.

7. The method of manufacturing a float glass according to any one of claims 1 to 6, wherein the plasma gas is ejected from a plasma ejection device provided to face an upper side of the molten metal exposed portion,

the plasma spraying device is provided with a plasma gas spraying part for spraying the plasma gas,

the plasma gas ejection section includes a plurality of plasma generation devices,

the electron density of the plasma gas in a plasma region in which the gas introduced into the plasma generating device is converted into plasma is 1 × 10¹³/cm³The above.

8. The method for producing float glass according to any one of claims 1 to 7, wherein the oxygen potential of the molten metal after plasma gas injection is 1/2 or less of the oxygen potential of the molten metal before plasma gas injection in the molten metal exposed portion.

9. The method of manufacturing a float glass according to any one of claims 1 to 8, wherein the temperature of the molten metal to which the plasma gas is injected is 900 ℃ or lower.

10. A float glass production apparatus, characterized in that it is a float glass production apparatus for forming a molten glass obtained by melting a glass raw material on a molten metal in a float bath into a glass ribbon, slowly cooling the obtained glass ribbon to obtain a glass sheet,

a plasma jet device is disposed above the molten metal exposed portion in the atmosphere in the float bath so as to be separated by a distance of 5 to 30mm in the vertical direction,

the plasma spraying device comprises a plasma gas spraying part and a supporting part for supporting the plasma gas spraying part,

the plasma gas injection unit injects a plasma gas to the molten metal exposed portion.

11. The manufacturing apparatus of a float glass according to claim 10, wherein the plasma gas injection part comprises a plurality of plasma generating devices,

the plasma generation device is disposed such that the longitudinal direction of the plasma generation device coincides with the flow direction of the glass ribbon.

12. The float glass manufacturing apparatus according to claim 11, wherein a cross-sectional shape of the gas discharge portion of the plasma generating apparatus is a rectangle.

Images