JP2017001899A - Manufacturing method of float glass, and manufacturing apparatus of float glass - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a polishing amount of a glass plate without adding a step in a polishing step.SOLUTION: A manufacturing apparatus of float glass includes a melting step for melting glass-making feedstock, a clarification step for clarifying molten glass, a shaping step for continuously supplying clarified molten glass onto molten metal 9 in a float bath 2 to shape a glass ribbon 5 on the molten metal 9, an annealing step for drawing the glass ribbon 5 from the float bath 2 by lift-out-rolls 7 and annealing the glass ribbon 5 to a strain point temperature or lower of glass while conveying the glass ribbon 5 by rear rolls 8. The annealing step includes a foreign matter removing step for removing foreign matters adhering to a bottom surface 5a of the glass ribbon 5 by supplying a gas containing a halogen element to the bottom surface 5a using injectors 20, 30 installed below the glass ribbon 5 and between the rear rolls 8.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a float glass manufacturing method and a float glass manufacturing apparatus.

In the production of glass plates by the float process, a glass ribbon is supplied from a glass melting kiln to a molten tin bath called a float bath, a glass ribbon is formed on the molten tin bath, and then a glass ribbon is formed by a transport roll called a lift-out roll. Is transferred to a slow cooling furnace. Usually, defects called dross (tin and tin oxide) are attached to the lower surface of the glass ribbon.
In a thin glass plate of less than 1.1 mm used for flat panel display applications such as liquid crystal, the size of dross (tin and tin oxide) adhering to the glass plate surface is about 10 μm according to the needs of customers. Therefore, it is necessary to remove even dross defects of the size allowed for general construction.

  In Patent Document 1, a plate-like carbon removing member made of carbon called a carbon seal is brought into contact with a lower portion of a lift-out roll to scrape and remove tin or tin oxide adhering to the lift-out roll. ing.

  In the thin glass sheet for liquid crystal manufactured by the float process, dross is removed at the same time because the lower surface of the glass plate is polished to satisfy the flatness required by the customer. In recent years, the amount of polishing of the glass plate in the polishing process has been reduced by the measure for improving the flatness in the melting and forming processes, and the productivity of the polishing process has been improved.

JP 11-335127 A JP-A-4-202028

However, as the polishing amount of the glass plate is reduced, there is a problem that the dross attached to the glass plate surface cannot be removed. Therefore, it is necessary to remove the dross at the previous stage of the polishing process. There are cases where dross cannot be completely removed by simply improving the removal member described in Patent Document 1.
Patent Document 2 proposes a method in which a float glass is brought into contact with an acid solution and then washed with water to remove attached tin, but this increases the number of processes, lowers the overall productivity, and increases costs. Become.

  The present invention has been made in view of the above problems, and an object thereof is to provide a float glass manufacturing method and a float glass manufacturing apparatus that can reduce the polishing amount of a glass plate in a polishing process without increasing the number of processes. And

  In order to solve the above-mentioned problems, the present invention provides a melting step for melting a glass raw material, a clarification step for clarifying the molten glass, and continuously supplying the clarified molten glass onto the molten metal of the float bath, A forming step of forming a glass ribbon on a metal, a slow cooling step of drawing out the glass ribbon from the float bath by a lift-out roll, and gradually cooling the glass ribbon to a temperature below the strain point of the glass while transporting the glass ribbon by a layer roll; The slow cooling step is performed between the layer rolls and using an injector installed below the glass ribbon, and supplying a gas containing a halogen element to the bottom surface of the glass ribbon. Provided is a float glass manufacturing method including a foreign matter removing step of removing foreign matter attached to a surface.

  In addition, the present invention provides a float bath for forming a glass ribbon on a molten metal, a lift box that includes a lift-out roll that pulls up the glass ribbon adjacent to the float bath, and adjacent to the dock box. And a slow cooling furnace that gradually cools the glass ribbon to a temperature below the strain point of the glass while being conveyed by a layer roll, and the slow cooling furnace is provided between the layer rolls and includes an injector installed below the glass ribbon, The injector provides a float glass manufacturing apparatus that removes foreign matter adhering to the bottom surface by supplying a gas containing a halogen element to the bottom surface of the glass ribbon.

  According to the float glass manufacturing method and the float glass manufacturing apparatus of the present invention, it is possible to reduce the polishing amount of the glass plate in the polishing step without increasing the number of steps.

It is explanatory drawing of the manufacturing process of the float glass which concerns on embodiment of this invention. It is a figure which shows typically the double flow type injector which concerns on embodiment of this invention. It is a figure which shows typically the single flow type injector which concerns on embodiment of this invention. 4 is a schematic diagram for explaining a test apparatus used for evaluation of Experimental Example 1. FIG.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. However, the present invention is not limited to the following embodiments, and the following embodiments are not departed from the scope of the present invention. Various modifications and substitutions can be made.

  In the present embodiment, a configuration example of the float glass manufacturing method of the present invention will be described.

  FIG. 1 is an explanatory diagram of a manufacturing process of float glass. Molten glass is continuously supplied onto the molten metal 9 of the float bath 2, and the glass ribbon 5 is formed on the molten metal 9 (forming step). In addition, although not shown in figure, the molten glass melt | dissolves a glass raw material in the melt | dissolution process of the upstream of FIG. 1, and also gave the clarification process in the clarification process.

  Next, the glass ribbon 5 is pulled out from the molten metal 9 of the float bath 2 by a plurality of lift-out rolls 7, and the glass ribbon 5 is lifted and conveyed at the exit of the float bath 2. A place where the lift-out mouth 7 exists is referred to as a mouth box 3.

  The glass ribbon 5 drawn out from the float bath 2 is gradually cooled to below the strain point temperature of the glass while being transported by a plurality of layer rolls 8 in the slow cooling furnace 4 in order to prevent cracking due to rapid shrinkage and reduction in flatness. (Slow cooling step). The glass ribbon 5 after slow cooling is cut into a desired size (cutting step).

  Hereinafter, of the pair of surfaces facing the thickness direction of the glass ribbon 5, the surface supported by the lift-out roll 7 or the layer roll 8 is referred to as a bottom surface 5a, and the other surface is referred to as a top surface 5b.

  When the use of the cut float glass is a glass substrate for a liquid crystal display, in order to improve the flatness of the glass substrate, there is further a polishing step for polishing the glass substrate. In the polishing step, the tin contact surface of the glass substrate is mainly subjected to mechanical polishing or chemical mechanical polishing. From the viewpoint of improving productivity, the polishing amount is preferably 3 μm or less, more preferably 2 μm or less, still more preferably 1.5 μm or less, and particularly preferably 1.0 μm or less.

  The float glass manufacturing method of the present embodiment contains halogen elements in the bottom surface 5a of the glass ribbon 5 using the injectors 20 and 30 installed between the layer rolls 8 below the glass ribbon 5 in the slow cooling step. There is a foreign matter removal step of supplying gas and removing foreign matters such as dross attached to the bottom surface 5a.

Although not shown in FIG. 1, in the above slow cooling step, SO ₂ gas is applied to the bottom surface 5 a of the glass ribbon 5 by using a protective layer forming device installed between the layer rolls 8 below the glass ribbon 5. And a protective layer forming step of forming a sulfate-preventing protective layer on the bottom surface 5a. The protective layer forming step may be provided before the foreign matter removing step or after the foreign matter removing step. In the protective layer forming step, a mixed gas of SO ₂ gas and air may be supplied.

  Next, the foreign matter removing step will be specifically described with reference to FIGS.

  FIG. 2 is a diagram schematically showing a double-flow injector 20 according to the embodiment of the present invention. FIG. 3 is a view schematically showing a single-flow injector 30 according to the embodiment of the present invention.

  The injectors 20 and 30 may be used in any manner, and two or more injectors 20 may be arranged in series in the moving direction of the glass ribbon 5 to treat the surface of the glass ribbon. As shown in FIG. 2, the double-flow injector 20 is an injector in which the gas flow from the supply port 21 to the exhaust port 25 is equally divided in the forward direction and the reverse direction with respect to the moving direction of the glass ribbon 5.

  The single-flow injector 30 is an injector in which the gas flow from the supply port 31 to the exhaust port 35 is fixed in either the forward direction or the reverse direction with respect to the moving direction of the glass ribbon 5. In the embodiment of FIG. 3, the gas flow from the supply port 31 to the exhaust port 35 is forward with respect to the moving direction of the glass ribbon 5.

  The gas blown from the supply ports 21, 31 of the injectors 20, 30 to the bottom surface 5 a of the glass ribbon 5 moves through the flow paths 24, 34 in the forward or reverse direction with respect to the moving direction of the glass ribbon 5, and exhausts It flows out to the mouths 25 and 35.

  The distance D between the supply ports 21 and 31 of the injectors 20 and 30 and the bottom surface 5a of the glass ribbon 5 is preferably 3 to 50 mm. The distance D is more preferably 5 mm or more, and further preferably 8 mm or more. The distance D is more preferably 40 mm or less, and further preferably 30 mm or less. By setting the distance D to 50 mm or less, the gas can be prevented from diffusing into the atmosphere, and a sufficient amount of gas can reach the bottom surface 5a of the glass ribbon 5 with respect to the desired gas amount. Further, by setting the distance D to be 3 mm or more, contact between the bottom surface 5a of the glass ribbon 5 and the injectors 20 and 30 can be avoided even if the glass ribbon 5 between the layer rolls 8 is bent.

  The distance L in the moving direction of the glass ribbon 5 of the injectors 20 and 30 is preferably 50 to 500 mm. The distance L is more preferably 100 mm or more, and further preferably 200 mm or more. The distance L is more preferably 400 mm or less. By setting the distance L to 500 mm or less, the distance between the layer rolls 8 can be shortened, so that the bending of the glass ribbon 5 is suppressed and dross can be uniformly removed. Moreover, the supply ports 21 and 31 and the exhaust ports 25 and 35 can be provided by making the distance L into 50 mm or more. The distance L of the injector 20 is preferably 100 mm or more, and the distance L of the injector 30 is preferably 50 mm or more.

  The distance in the direction perpendicular to the moving direction of the glass ribbon 5 of the injectors 20 and 30 is preferably equal to or greater than the product area of the glass ribbon 5 in that direction. Preferably it is 3000 mm or more, More preferably, it is 4000 mm or more.

  Further, it is preferable that the supply ports 21 and 31 for supplying a gas containing a halogen element and the exhaust ports 25 and 35 face the bottom surface 5 a of the glass ribbon 5.

  In the present embodiment, the temperature of the glass ribbon 5 when the gas containing a halogen element is supplied to the bottom surface 5a of the glass ribbon 5 being conveyed to treat the bottom surface 5a is 400 to 900 ° C. Preferably, it is 500-800 degreeC. The effect of removing a tin defect by a gas containing a halogen element is more effective as it is carried out at a higher temperature.

In the foreign matter removing process of the present embodiment, when the gas containing a halogen element is hydrogen chloride (HCl) gas, for example, dross (tin and tin oxide) adhering to the bottom surface 5a of the glass ribbon 5 is removed. It is removed by the following reaction mechanism.
SnO ₂ + 2HCl → SnCl ₂ + H ₂ O + 1 / 2O ₂ (1)
In order to remove tin oxide, it is preferable to produce tin chloride (SnCl ₂ ) by reacting tin oxide (SnO ₂ ) and hydrogen chloride (HCl) as in the above formula (1).
In addition, hydrogen (H ₂ ) gas is added to hydrogen chloride (HCl) gas,
SnO ₂ + 2H ₂ → Sn + 2H ₂ O (2)
Sn + 2HCI → SnCl ₂ + H ₂ (3)
By doing so, tin oxide can be more efficiently removed.

Instead of hydrogen (H ₂ ) in the above formula (2), carbon monoxide (CO), methane (CH ₄ ), ethane (C ₂ H ₆ ), propane (C ₃ H ₈ ), butane (C ₄ H ₁₀₎ ), Ethylene (C ₂ H ₄ ), propene (C ₃ H ₆ ), acetylene (C ₂ H ₂ ), propyne (C ₃ H ₄ ), hydrogen sulfide (H ₂ S), sulfur dioxide (SO ₂ ), one Nitrogen oxide (NO) or ammonia (NH ₃ ) may be used.

The reaction temperature of the above formulas (1) and (3) is preferably 630 ° C. or higher. This is because the boiling point of tin chloride (SnCl ₂ ) generated by the above formulas (1) and (3) is 623 ° C., and tin chloride (SnCl ₂ ) generated from the bottom surface 5a of the glass ribbon 5 is volatilized.

  Even when the chlorine-containing gas is other than hydrogen chloride (HCl) gas, tin defects are removed by the same reaction mechanism as described above.

In the foreign matter removing process of the present embodiment, hydrogen chloride (HCl), chlorine (Cl ₂ ), silicon tetrachloride (SiCl ₄ ), sulfur dichloride (SCl ₂ ), disulfur dichloride (S) are used as the gas containing chlorine. ₂ Cl _2), phosphorus trichloride _(PCl 3), phosphorus pentachloride _(PCl 5), iodine trichloride _(I 2 _Cl 6), nitrogen trichloride _(NCl 3), iodine monochloride (ICl), bromine monochloride ( BrCl) or chlorine trifluoride (ClF ₃ ) can be used.

  Among these, hydrogen chloride (HCl) gas is preferable for reasons such as cost and a well-known handling method.

Further, as a gas containing a halogen element, in addition to a gas containing chlorine, fluorine (F ₂ ), bromine (Br ₂ ), hydrogen fluoride (HF), hydrogen bromide (HBr), or hydrogen iodide ( HI) can be used.

  In the foreign matter removing step of the present embodiment, the gas containing a halogen element may be sprayed on the bottom surface 5a of the glass ribbon 5 as a single gas, but the supply ports 21 and 31 used for spraying these gases are used. From the viewpoint of preventing corrosion of the equipment, it is preferable to use an inert gas such as nitrogen or a rare gas as a carrier gas and spray it as a mixed gas with these carrier gases.

When a reducing gas such as hydrogen (H ₂ ) is added to a gas containing a halogen element, the gas containing the halogen element and the reducing gas may be sprayed from separate supply ports (not shown). Alternatively, both gases may be mixed in advance and sprayed from the same supply ports 21 and 31 as a mixed gas.

  When both gases are sprayed from separate supply ports, the reducing gas may be sprayed upstream of the gas containing the halogen element in the moving direction of the glass ribbon 5, or both gases may be the same. You may spray in position.

  The composition of the float glass of the present invention is not particularly limited, and may be a glass composition containing an alkali metal component such as soda lime glass, or a non-alkali glass composition substantially free of an alkali metal component. Also good. In particular, it is suitable for the production of float glass having a non-alkali glass composition widely used as a glass substrate for liquid crystal displays.

  Next, the structural example of the float glass manufacturing apparatus of this invention is demonstrated.

  The float glass of this invention is manufactured using the float glass manufacturing apparatus 1 as shown in FIG. In FIG. 1, as described above, the molten glass is continuously supplied onto the molten metal 9, and the float bath 2 for forming the glass ribbon 5 on the molten metal 9 is provided. Although not shown, the molten glass is obtained by melting a glass raw material in a melting furnace on the upstream side of FIG. A door box 3 having a lift-out roll 7 for pulling up the glass ribbon 5 is disposed adjacent to the float bath 2. Further, a slow cooling furnace 4 is disposed adjacent to the door box 3, and the slow cooling furnace 4 can gradually cool the glass ribbon 5 to a temperature below the strain point of the glass while being conveyed by the layer roll 8. Although not shown in FIG. 1, the glass ribbon 5 after slow cooling is cut into a desired size by a cutting device.

  Although not shown in FIG. 1, when the use of the cut float glass is a glass substrate for a liquid crystal display, the float glass manufacturing apparatus further polishes the glass substrate in order to improve the flatness of the glass substrate. Have the device. The polishing apparatus mainly performs mechanical polishing or chemical mechanical polishing on the tin contact surface of the glass substrate. From the viewpoint of improving productivity, the polishing amount is preferably 3 μm or less, more preferably 2 μm or less, still more preferably 1.5 μm or less, and particularly preferably 1.0 μm or less.

  The float glass manufacturing apparatus 1 of the present embodiment includes injectors 20 and 30 installed between the layer rolls 8 below the glass ribbon 5 in the slow cooling furnace 4. The injectors 20 and 30 supply a gas containing a halogen element to the bottom surface 5a of the glass ribbon 5 to remove foreign matters such as dross attached to the bottom surface 5a.

Although not shown in FIG. 1, the float glass manufacturing apparatus 1 includes a protective layer forming apparatus installed between the layer rolls 8 below the glass ribbon 5 in the slow cooling furnace 4. The protective layer forming apparatus supplies SO ₂ gas to the bottom surface 5a of the glass ribbon 5, and forms a protective layer for preventing sulfate wrinkles on the bottom surface 5a. The protective layer forming apparatus may be provided upstream of the injectors 20 and 30 in the moving direction of the glass ribbon 5 or may be provided downstream. The protective layer forming apparatus may supply a mixed gas of SO ₂ gas and air.

  The configuration of the injectors 20 and 30 and the type of gas used for the injectors 20 and 30 can be configured in the same manner as in the float glass manufacturing method, and thus the description thereof is omitted.

(Experimental example 1)
(Examples 1 to 11)
FIG. 4 is a schematic diagram for explaining the test apparatus used for the evaluation of Experimental Example 1. Float glass (manufactured by Asahi Glass Co., Ltd .: AN100) is prepared so as to have a plate thickness of 0.5 mm, cut into 10 mm squares, and a glass plate having one dross on the tin contact surface for each glass plate 40 Ten 40 pieces were obtained.

In Example 1, as shown in FIG. 4, the glass plate 40 is placed in a 25 mL volume carbon box 41 having an opening for inserting the gas introduction nozzle 43 with the tin contact surface facing upward. After putting in the quartz tube 42 with a volume of 4 L, the quartz tube 42 was heated with an electric heater for 2 minutes, and the temperature of the glass plate 40 was raised to 600 degreeC. While the heated glass plate 40 is kept at 600 ° C. for 1 minute, the inlet of the gas introduction nozzle 43 having an inner diameter of 6 mm is directed to the wall surface of the carbon box 40 and nitrogen (N ₂ ) gas is used as a carrier gas to 5.0 vol. % Hydrogen chloride (HCl) gas was introduced at a flow rate of 2.5 L / min for 3 seconds to perform gas treatment in which a gas having a linear velocity of 40 cm / sec was blown onto the glass plate 40. Thereafter, the glass plate 40 was cooled to room temperature over 30 minutes while introducing nitrogen (N ₂ ) gas at a flow rate of 2.5 L / min using the gas introduction nozzle 43.

Next, a polishing pad made of polyurethane foam (D hardness of 30 degrees) and cerium oxide as a polishing agent are used so that the polishing amount of the tin contact surface of the gas-treated glass plate 40 becomes an average of 0.8 μm. Chemical mechanical polishing was performed with a predetermined polishing load (50 g / cm ² ) using a 4B single-side polishing machine. Here, 4B represents that the size of the carrier put into the polishing machine is 4 inches. All the dross of the ten glass plates 40 was removed. The dross residual rate of the glass plate after chemical mechanical polishing was 0%.

In Examples 2 to 10, the conditions of hydrogen chloride (HCl) gas concentration, glass plate temperature, or hydrogen (H ₂ ) gas concentration were changed as shown in Table 1 by the same evaluation method as in Example 1.

  Table 1 shows the evaluation results of Examples 1 to 11. Examples 1 to 10 are Examples, and Example 11 is a Comparative Example. It was confirmed that the dross residual rate was lowered when hydrogen chloride (HCl) gas of 0.1 vol% or more was used.

(Examples 21 to 28)
In Example 21, chemical mechanical polishing was performed so that the average polishing amount was 0.5 μm. Otherwise, gas treatment and chemical mechanical polishing were carried out in the same manner as in Example 1, and all the dross of the ten glass plates 40 were removed. The dross residual rate of the glass plate after chemical mechanical polishing was 0%.
In Examples 22 to 28, the conditions for hydrogen chloride (HCl) gas concentration or hydrogen (H ₂ ) gas concentration were changed as shown in Table 2 by the same evaluation method as in Example 21.

  Table 2 shows the evaluation results of Examples 21 to 28. Examples 21 to 27 are examples, and example 28 is a comparative example. It was confirmed that the dross residual rate was lowered when hydrogen chloride (HCl) gas of 0.1 vol% or more was used.

(Experimental example 2)
(Examples 31-36)
In Example 31, as shown in FIGS. 1 and 2, a double-flow type injector 20 was inserted between the layer rolls 8 in the slow cooling furnace 4 at a position where the glass ribbon 5 having a thickness of 0.7 mm was 660 ° C. The distance D between the supply port 21 of the injector 20 and the bottom surface 5a of the glass ribbon 5 was 10 mm. The distance L in the moving direction of the glass ribbon 5 of the injector 20 was 300 mm. Using the injector 20, 20 vol% hydrogen chloride (HCl) gas added with 10 vol% hydrogen (H ₂ ) gas using nitrogen (N ₂ ) gas as a carrier gas was applied to the glass ribbon 5 at a linear velocity of 100 cm / sec. Sprayed to the bottom surface 5a.

  Float glass (manufactured by Asahi Glass Co., Ltd .: AN100) produced by slowly cooling and cutting the glass ribbon 5 is cut into 50 mm squares, and a glass plate having one dross on the tin contact surface is provided for each glass plate. Five sheets were obtained.

  Next, on the gas-treated surface, a 4B single-side polishing machine using a polyurethane polyurethane polishing pad (D hardness of 30 degrees) and cerium oxide as an abrasive so that the average polishing amount is 0.3 μm. Chemical mechanical polishing was performed at a predetermined polishing load (50 g / cm 2). Dross of 4 out of 5 glass plates was removed. The dross remaining rate of the glass plate after chemical mechanical polishing was 20%.

In Examples 32-36, the conditions of hydrogen chloride (HCl) gas concentration, glass plate temperature, or hydrogen (H ₂ ) gas concentration were changed as shown in Table 3 by the same evaluation method as in Example 31.

  Table 3 shows the evaluation results of Examples 31 to 36. Examples 31, 32, 34, and 35 are Examples, and Examples 33 and 36 are Comparative Examples. It was confirmed that when hydrogen chloride (HCl) gas of 0.5 vol% or more was used, the dross residual rate was lowered. Moreover, it was confirmed that the dross residual rate was lowered by raising the glass plate temperature from 660 ° C. to 680 ° C.

  As described above, the float glass manufacturing method and the float glass manufacturing apparatus have been described in detail and with reference to specific embodiments, but the present invention is not limited to the above embodiments and the like, and departs from the spirit and scope of the present invention. It will be apparent to those skilled in the art that various changes and modifications can be made without doing so.

DESCRIPTION OF SYMBOLS 1 Float glass manufacturing apparatus 2 Float bath 3 Dross box 4 Slow cooling furnace 5 Glass ribbon 5a Bottom surface 5b Top surface 7 Lift-out roll 8 Layer roll 9 Molten metal 20, 30 Injector 21, 31 Supply port 24, 34 Channel 25, 35 Exhaust port 40 Glass plate 41 Carbon box 42 Quartz tube 43 Gas introduction nozzle

Claims (9)

A melting step of melting the glass raw material, a clarification step of clarifying the molten glass, a molding step of continuously supplying the clarified molten glass onto the molten metal of the float bath, and forming a glass ribbon on the molten metal; And a slow cooling step in which the glass ribbon is pulled out from the float bath by a lift-out roll and gradually cooled to below the strain point temperature of the glass while transporting the glass ribbon by a layer roll.
The slow cooling step is between layer rolls and is attached to the bottom surface by supplying a gas containing a halogen element to the bottom surface of the glass ribbon using an injector installed below the glass ribbon. A float glass manufacturing method comprising a foreign matter removing step of removing foreign matter. The gas containing the halogen element is hydrogen chloride (HCl), chlorine (Cl ₂ ), silicon tetrachloride (SiCl ₄ ), sulfur dichloride (SCl ₂ ), disulfur dichloride (S ₂ Cl ₂ ), trichloride. Phosphorus (PCl ₃ ), phosphorus pentachloride (PCl ₅ ), iodine trichloride (I ₂ Cl ₆ ), nitrogen trichloride (NCl ₃ ), iodine monochloride (ICl), bromine monochloride (BrCl), and trifluoride The method for producing a float glass according to claim 1, wherein the float glass is one or more gases selected from the group consisting of chlorine (ClF ₃ ).   The method for producing a float glass according to claim 1, wherein the gas containing a halogen element is 0.1 vol% or more of hydrogen chloride (HCl) gas.   The float glass manufacturing method of any one of Claims 1-3 which added reducing gas to the gas containing the said halogen element. The reducing gas includes hydrogen (H ₂ ), carbon monoxide (CO), methane (CH ₄ ), ethane (C ₂ H ₆ ), propane (C ₃ H ₈ ), butane (C ₄ H ₁₀ ), ethylene (C ₂ H ₄ ), propene (C ₃ H ₆ ), acetylene (C ₂ H ₂ ), propyne (C ₃ H ₄ ), hydrogen sulfide (H ₂ S), sulfur dioxide (SO ₂ ), nitric oxide ( The float glass manufacturing method according to claim 4, which is one or more gases selected from the group consisting of NO) and ammonia (NH ₃ ).   The float glass manufacturing method of any one of Claims 1-5 which supplies the gas containing the said halogen element when the temperature of the said glass ribbon is 500-800 degreeC.   The float glass manufacturing method according to claim 1, wherein the foreign matter attached to the bottom surface is dross. The slow cooling step is performed between the layer rolls and using a protective layer forming apparatus installed below the glass ribbon, and supplying SO ₂ gas to the bottom surface of the glass ribbon, thereby providing sulfate on the bottom surface. The float glass manufacturing method of any one of Claims 1-7 which has a protective layer formation process which forms the protective layer for preventing wrinkles. A float bath for forming a glass ribbon on the molten metal, a mouth box having a lift-out roll for pulling up the glass ribbon adjacent to the float bath, a door box adjacent to the mouth box, and the glass ribbon A slow cooling furnace that gradually cools to a temperature below the strain point of the glass while being conveyed by a layer roll,
The slow cooling furnace is between layer rolls, and includes an injector installed below the glass ribbon,
The float glass manufacturing apparatus, wherein the injector removes foreign matter adhering to the bottom surface by supplying a gas containing a halogen element to the bottom surface of the glass ribbon.

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