TW201345849A - Glass plate - Google Patents

Abstract

The present invention relates to a glass plate formed by causing molten glass, which is continuously fed onto a molten metal (e.g., molten tin) in a float bath, to flow on the molten metal, wherein the sulfur concentration in the glass at a position at a depth of 0.3 to 0.5 mum from the top surface exposed to a reductive atmosphere in the float bath is equivalent to or greater than the sulfur concentration at a position at a depth of 3 mum from the top surface.

Description

glass plate

The present invention relates to a glass sheet.

As a method of forming a glass sheet, a floating method is widely used. In the floating method, the molten glass continuously supplied to the molten metal (for example, molten tin) in the molten metal tank (hereinafter, simply referred to as "slot") flows on the molten metal to form a strip shape (for example, refer to the patent) Document 1).

In many cases, the environment in the tank is a reducing environment containing hydrogen gas in order to prevent oxidation of the molten metal. Hydrogen prevents oxidation of the molten metal by reacting with oxygen mixed from the outside.

On the other hand, Patent Document 1 discloses a case where the environment in the tank is an oxidizing environment. The oxidizing environment lowers the surface tension of the molten glass, so the molten glass is easily formed. As the oxidizing environment, those containing sulfurous acid (SO ₂ ) gas and sulfur trioxide (SO ₃ ) gas are preferably described.

Further, since the sulfurous acid gas and the sulfur trioxide gas are hydrogen sulfide (H ₂ S) gas or the like in a reducing atmosphere containing hydrogen gas, they cannot be stably present, and thus the surface tension of the molten glass cannot be lowered.

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Publication No. Sho 46-41915

The prior glass sheets have a large number of minute defects formed on the main surface exposed to the reducing environment in the groove, and there is room for improvement in bending strength.

The present invention has been made in view of the above problems, and an object thereof is to provide a glass sheet excellent in bending strength.

In order to solve the above object, a glass sheet according to an aspect of the present invention is formed by flowing a molten glass continuously supplied onto a molten metal in a molten metal tank onto the molten metal. The glass plate is at a distance of 0.3 to 0.5 μm from the main surface exposed to the reducing environment in the molten metal bath, and the sulfur concentration of the glass is greater than or equal to a depth of 3 μm from the main surface. The concentration of sulfur in the glass at the location.

According to the present invention, a glass sheet excellent in bending strength is provided.

10‧‧‧metal tank

12‧‧‧ Entrance to the metal tank

14‧‧‧Export of metal tank

20‧‧‧ molten metal

30‧‧‧Solid glass

40‧‧‧Return environment

50‧‧‧Roughing lip brick

60‧‧‧heater

70‧‧‧ gas supply pathway

80‧‧‧Exhaust passage

Fig. 1 is a view showing the distribution of sulfur concentration in a glass plate according to an embodiment of the present invention.

Fig. 2 is an explanatory view (1) of a manufacturing apparatus of a glass sheet according to an embodiment of the present invention.

Fig. 3 is an explanatory view (2) of a manufacturing apparatus for a glass sheet according to an embodiment of the present invention.

Hereinafter, embodiments for carrying out the invention will be described with reference to the drawings. In the following drawings, the same or corresponding reference numerals are given to the same or corresponding components, and the description is omitted.

The method for producing a glass sheet according to the present embodiment includes, for example, a melting step, a molding step, a slow cooling step, and a cutting step, and further has a polishing step as needed. The grinding step is carried out according to the use of the glass plate.

The melting step melts the glass raw material prepared by mixing a plurality of raw materials to obtain molten glass. After the glass raw material is put into the melting furnace, the flame is sprayed by the self-burning burner The glass raw material is melted by the heat generation to become molten glass.

The forming step is that the molten glass obtained in the melting step is continuously supplied to the molten metal (for example, molten tin) in the tank, and the molten glass is flowed on the molten metal to be formed, thereby obtaining a sheet glass (so-called glass ribbon). This forming method is called a floating method. In order to prevent oxidation of the molten metal, the environment in the tank is set to a reducing environment containing hydrogen. The sheet glass is cooled while flowing in a specific direction, and is pulled from the molten metal in the vicinity of the outlet of the groove.

The slow cooling step is performed in the slow cooling furnace to slowly cool the sheet glass obtained in the forming step. The plate glass is placed in a slow cooling furnace, and is cooled while being horizontally conveyed from the inlet of the slow cooling furnace toward the outlet on the roll. In the slow cooling furnace, sulfurous acid (SO ₂ ) gas or the like is blown to the surface of the sheet glass near the inlet of the slow cooling furnace to form a sulfate film on the surface layer of the sheet glass. The outlet of the slow cooling furnace is open to the atmosphere, so the environment inside the cooling furnace is an atmospheric environment.

The cutting step is performed by cutting the plate glass which is slowly cooled in the slow cooling step by the cutter to a specific size. In the cutting step, both edge portions (so-called ears) in the width direction of the sheet glass are cut. The reason for this is that both edge portions in the width direction of the sheet glass become thick due to the influence of surface tension or the like.

The grinding step is to grind the main surface of the glass sheet obtained in the cutting step. In the polishing step, the main surface (hereinafter referred to as "bottom surface") in contact with the molten metal in the groove is polished according to the use of the glass plate. The main surface (hereinafter referred to as "top surface") exposed to the main surface on the opposite side to the bottom surface and exposed to the reducing atmosphere in the groove is not polished.

A glass plate as a product was obtained in the above manner. The glass plate can be used, for example, as a window glass for a vehicle, a window glass for a building, a substrate for a display, a cover glass for a display, or a substrate for a photomask. "Monitor" includes liquid crystal display (LCD), plasma display panel (PDP, Plasma Display Panel), organic Flat panel display (FPD) such as EL (Electroluminescence) display.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a graph showing the distribution of sulfur concentration in a glass plate according to an embodiment of the present invention. In Fig. 1, the distribution of the sulfur concentration of the glass plate of the present embodiment is indicated by a solid line, and the distribution of the sulfur concentration of the previous glass plate is indicated by a broken line. The vertical axis represents the sulfur concentration (atoms/cm ³ ) in the glass, and the horizontal axis represents the depth (μm) from the top surface. The sulfur concentration in the glass was measured by cutting a top surface by a secondary ion mass spectrometer (SIMS).

The distribution of the sulfur concentration in the glass sheet is affected by the concentration of sulfur in the reducing environment in the forming step. If the sulfur concentration in the reducing environment is low, sulfur as a volatile component easily leaks from the upper surface of the molten glass (the top surface of the glass plate) to the reducing environment. If the concentration of sulfur in the reducing environment is high, the sulfur in the reducing environment easily enters the upper surface of the molten glass. Further, the distribution of the sulfur concentration in the glass plate is also affected by the SO ₂ gas used in the slow cooling step.

As shown by the solid line and the broken line in Fig. 1, the position of the top surface is less than 0.05 μm, and the closer to the top surface, the more the sulfur concentration in the glass increases. The reason for this is that it is affected by the SO ₂ gas used in the slow cooling step. The slow cooling step is lower in temperature than the forming step, and therefore the depth of the position affected by the external gas is shallower than the forming step. Further, the position in the process of forming in the groove is affected by the environment, and the position at a depth of 3 μm or more from the top surface is too deep, so the sulfur concentration in the glass is fixed.

Unlike the previous glass plate, the glass plate of the present embodiment has a depth of 0.3 to 0.5 μm from the top surface (affected by the external gas in the forming step and is substantially unaffected by the external gas in the slow cooling step). The sulfur concentration of the glass on the glass is greater than or equal to the sulfur concentration of the glass at a position of 3 μm from the top surface (substantially free from the position of the external gas in the forming step and the slow cooling step). Therefore, it will be described in detail later, as a volatile component of sulfur in the forming step from the upper surface of the molten glass (glass plate) The top surface) is less likely to leak out into the reducing environment, and there are substantially no micro defects (including phase separation of the glass) on the top surface.

Further, as shown by the solid line in Fig. 1, the glass plate of the present embodiment has a depth of 0.05 to 0.3 μm from the top surface, and the closer to the top surface, the lower the sulfur concentration in the glass. The reason for this phenomenon is that it is affected by the supply of sulfur-containing gas to the upstream side in the tank in the forming step. On the upstream side of the tank, the sulfur concentration in the reducing environment is higher, and on the downstream side in the tank, the sulfur concentration in the reducing environment becomes lower. Therefore, it can be considered that the sulfur entering the upper surface of the molten glass (the top surface of the glass plate) from the reducing environment on the upstream side of the groove leaks into the reducing environment on the downstream side of the groove.

As described above, the glass plate of the present embodiment has substantially no micro defects (hereinafter referred to as minute defects) in the glass lattice on the top surface. Therefore, the bending strength when the tensile stress is applied to the top surface is good. The flexural strength was measured by a ball on ring method. The details of the method for measuring the bending strength will be described in the examples.

The bending strength depends on the type of the glass of the glass plate or the thickness of the glass plate. When the thickness is 0.2 to 0.7 mm (preferably 0.5 to 0.7 mm), the bending strength is, for example, 4 GPa or more. Further, in the case of a soda lime glass plate having a thickness of 0.2 to 0.7 mm (preferably 0.5 to 0.7 mm), the bending strength is, for example, 2.5 GPa or more.

Further, since the glass plate of the present embodiment has substantially no minute defects on the top surface, in order to remove the dirt on the surface or roughen the surface and perform surface treatment with a solution of buffered hydrofluoric acid, since there is no starting point, foreign matter can be suppressed. The haze value (turbidity) after adhesion and surface treatment was good. The term "haze" refers to the percentage of transmitted light that is deviated from the incident light by 2.5 or more by forward scattering in the transmitted light of the glass plate (JIS K7136; 2000). The optical axis of the incident light is set to be parallel to the thickness direction of the glass plate. The details of the method for measuring the haze value will be described in the examples.

The haze value depends on the type of the glass of the glass plate, etc., and in the case of an alkali-free glass, the haze value is, for example, 1% or less, preferably 0.5% or less, more preferably 0.2% or less. Further, in the case of soda lime glass, the haze value is, for example, 3% or less, preferably 1%. More preferably, it is 0.5% or less.

The type of glass of the glass plate is selected according to the use of the glass plate. For example, in the case of a glass substrate for LCD, an alkali-free glass is used. Further, in the case of a window glass for a vehicle, a window glass for a building, and a glass substrate for a PDP, soda lime glass is used. In the case of a cover glass for a display, a chemically strengthened soda lime glass is mainly used. In the case of a substrate for a photomask, quartz glass having a low coefficient of thermal expansion is mainly used.

The alkali-free glass may contain, for example, 50 to 66% of SiO ₂ , 10.5 to 24% of Al ₂ O ₃ , 0 to 12% of B ₂ O ₃ , 0 to 8% of MgO, and 0% by mass based on the oxide. ~14.5% CaO, 0~24% SrO, 0~13.5% BaO, 0~5% ZrO ₂ , 0~3% SnO, and MgO+CaO+SrO+BaO is 9~29.5%, alkali The total amount of the metal oxide is 0.1% or less.

The alkali-free glass preferably contains 58 to 66% of SiO ₂ , 15 to 22% of Al ₂ O ₃ , 5 to 12% of B ₂ O ₃ , and 0 to 8% of MgO based on the mass % of the oxide. 0~9% CaO, 3~12.5% SrO, 0~2% BaO, 0~1% SnO, and MgO+CaO+SrO+BaO is 9~18%, the content of alkali metal oxide The total amount is below 0.1%.

Since the alkali-free glass is limited by the foaming of the molten glass in the forming step, the sulfur concentration of the main body can be 1% by mass or less. "Main body" means the central portion of the glass plate in the thickness direction. The sulfur concentration of the main body is, for example, 0.1% by mass or more, preferably 0.2% by mass or more. When the sulfur concentration of the main body is 0.1% by mass or more, the sulfur volatilized from the molten glass in the forming step tends to aggregate in the reducing environment, and the sulfur concentration in the reducing environment tends to be high. When the sulfur concentration in the reducing atmosphere is sufficiently increased, the volatilization of the molten glass supplied from the melting furnace to the tank thereafter is suppressed. Further, in the case where the glass raw material having a relatively high temperature is melted, most of the sulfur contained in the glass raw material is volatilized into the environment in the melting furnace, so that the sulfur concentration of the main body may be less than 0.1% by mass. The temperature of the melting furnace is higher than the temperature in the tank.

The soda lime glass contains, for example, 65 to 75% of SiO ₂ , 0 to 13% of Al ₂ O ₃ , 0 to 15% of CaO, 0 to 15% of MgO, and 10 to 20% by mass based on the oxide. Na ₂ O, 0~10% K ₂ O, 0~5% Li ₂ O, 0~3% Fe ₂ O ₃ , 0~5% TiO ₂ , 0~3% CeO ₂ , 0 ~10% BaO, 0~5% SrO, 0~5% B ₂ O ₃ , 0~5% ZnO, 0~10% ZrO ₂ , 0~3% SnO ₂ , 0~0.5% SO ₃ .

Next, details of the forming step of the above glass sheet will be described based on FIGS. 2 and 3.

2 and 3 are explanatory views of a manufacturing apparatus of a glass sheet according to an embodiment of the present invention. Figure 2 is a top cross-sectional view of the groove, and Figure 3 is a side cross-sectional view of the groove.

In the molding step, the molten glass 30 is cooled while flowing on the molten metal 20 in the tank 10, and is formed into a strip shape. In order to prevent oxidation of the molten metal 20, the upper space in the tank 10 is filled with a reducing atmosphere 40 containing hydrogen. In order to prevent intrusion of outside air, the upper space in the tank 10 is maintained at a positive pressure higher than atmospheric pressure. In the tank 10, a laundering lip 50, a heater 60, an air supply passage 70, an exhaust passage 80, and the like are provided.

A spout lip 50 is a supply passage for supplying the molten glass 30 into the tank 10, and is provided on the inlet 12 of the tank 10. The runner lip tile 50 is connected to a melting furnace for making the molten glass 30.

The heater 60 is heated in the tank 10, for example, as shown in Fig. 3, and is suspended from the top of the tank 10. The heater 60 is provided in plural, for example, in a flow direction (X direction) and a width direction (Y direction) of the molten glass 30, and is arranged in a matrix. The X direction and the Y direction are horizontal directions orthogonal to each other.

The output of the heater 60 is controlled such that the temperature of the molten glass 30 becomes lower as the inlet 12 from the tank 10 faces the outlet 14. Further, the output of the heater 60 is controlled such that the thickness of the molten glass 30 becomes uniform in the width direction (Y direction).

The gas supply passage 70 is a passage for supplying a reducing gas into the tank 10, and is provided, for example, at the top of the tank 10 as shown in Fig. 3 . The air supply passage 70 is provided with a plurality of strips in a specific direction (X direction) with an interval therebetween.

The reducing gas may be a mixed gas of hydrogen and nitrogen. The ratio of hydrogen in the reducing gas is, for example, 0.1 to 15% by volume.

The exhaust passage 80 is a passage for exhausting the reducing environment 40, and is provided, for example, on the side wall of the tank 10 as shown in FIG. The exhaust passage 80 is provided with a plurality of strips in a specific direction (X direction) with an interval therebetween.

As shown in FIG. 3, the molten glass 30 is formed into a plate-like plate glass (glass ribbon) which is attached to the vicinity of the outlet 14 of the groove 10, and is pulled from the molten metal 20. Thereafter, the sheet glass is subjected to a slow cooling step, a cutting step, or the like to form a glass plate as a product.

The sulfur concentration in the reducing atmosphere 40 is set to be 1 mg/Nm ³ or more (preferably 5 mg/Nm ³ or more) above at least a part of the molten glass 30 so that the glass plate has a specific sulfur concentration distribution.

The sulfur in the reducing environment 40 is mainly present as a gas of the compound. Examples of the compound include hydrogen sulfide (H ₂ S) and the like. The hydrogen sulfide gas reacts with the upper surface of the molten glass 30 as in the following formula (1) to increase the sulfur concentration of the glass, and suppresses the volatilization of sulfur from the upper surface of the molten glass 30 to the reducing environment.

H ₂ S+Si-OR ²⁺ -O-Si → Si-OH+Si-OH+RS...(1)

In the formula (1), R represents an alkaline earth metal.

Further, the sulfur contained in the glass is volatilized into the reducing atmosphere by, for example, being exposed to hydrogen (H ₂ ) as in the following formula (2).

SO ₂ +3H ₂ → H ₂ S+2H ₂ O...(2)

The lower surface of the molten glass 30 is not exposed to hydrogen gas, so that it is difficult for sulfur to leak from the lower surface of the molten glass 30 to the outside, so that it is difficult to cause minute defects on the bottom surface.

The concentration of sulfur in the reducing atmosphere 40 is set to be 1 mg/Nm ³ or more above at least a portion of the molten glass 30, whereby the volatilization of sulfur from the upper surface of the molten glass 30 to the reducing environment can be suppressed, and the top surface can be reduced. Minor defects.

The volatilization of sulfur in the molten glass 30 is more likely to occur on the side where the temperature is higher. Therefore, in order to sufficiently obtain the above effects, it is preferred that the viscosity at least the molten glass 30 becomes 10 ⁶ dPa. Above the position below s, the sulfur concentration in the reducing environment 40 is 1 mg/Nm ³ or more. More preferably, the range is 5 mg/Nm ³ or more.

Here, as the viscosity of the molten glass 30, the viscosity in the center in the width direction of the molten glass 30 is used as a representative value. Further, the viscosity of the center of the molten glass 30 in the width direction is 10 ⁶ dPa. The sulfur concentration in the reducing environment 40 on the downstream side (low temperature side) of the position of s is not particularly limited, and may be 1 mg/Nm ³ or more, or may be less than 1 mg/Nm ³ .

When the sulfur concentration in the reducing atmosphere 40 is excessive, a solid sulfide is generated and falls to the upper surface of the molten glass 30. Therefore, in order to suppress the fall of the sulfide, the sulfur concentration in the reducing atmosphere 40 may be, for example, 10 mg/Nm ³ or less.

The adjustment of the sulfur concentration in the reducing atmosphere 40 is not particularly limited, and is performed, for example, by adjusting the amount of sulfur or sulfur compound supplied to the molten metal 20. The higher the sulfur concentration in the molten metal 20 becomes, the more the amount of sulfur released from the molten metal 20 to the reducing environment 40 increases, and thus the sulfur concentration in the reducing environment 40 becomes higher.

The supply of the sulfur or sulfur compound to the molten metal 20 can be carried out at any position in the groove 10 as long as it is carried out on the upper surface of the molten metal 20 which is not covered by the molten glass 30. This is because the molten metal 20 also flows along with the flow of the molten glass 30, so that the molten metal 20 is homogenized.

As the sulfur compound, for example, a sulfide such as tin sulfide (SnS) or a sulfate such as calcium sulfate (CaSO ₄ ) can be used, and the valence of sulfur is not particularly limited. Among these, it is preferable to suppress the sulfide which is contaminated and deteriorated as the molten tin of the molten metal 20 and has a high boiling point.

The sulfur concentration in the molten metal 20 is set according to the capacity or configuration of the tank 10, the feed gas speed of the reducing environment 40, the exhaust gas velocity, and the like, and is, for example, 1 mass ppm or more, preferably 3 mass ppm or more. When it is 1 mass ppm or more, the sulfur concentration in the reducing environment 40 can be made 1 mg/Nm ³ or more above at least a part of the molten glass 30. Further, in order to prevent the solid tin sulfide from adhering to the bottom surface or the top surface and becoming a defect, the sulfur concentration in the molten metal 20 may be 30 ppm by mass or less.

The higher the temperature of the molten metal 20 becomes, the more the amount of sulfur released from the molten metal 20 into the reducing environment 40 increases. As shown in FIG. 2, when a plurality of exhaust passages 80 are provided at intervals in the X direction, gas does not easily flow in the X direction. Therefore, the sulfur concentration in the reducing environment 40 is higher on the upstream side (high temperature side). The value gets higher.

The adjustment of the sulfur concentration in the reducing environment 40 can also be carried out by adjusting the supply amount of the sulfur-containing gas into the tank 10. The sulfur-containing gas may be supplied separately from the reducing gas, or may be supplied to the self-supply gas passage 70 by being mixed in the reducing gas. When the supply of the self-supply gas passage 70 is performed, the sulfur-containing gas may be supplied only from the supply passage 70 on the upstream side of the plurality of feed passages 70. The sulfur-containing gas is not particularly limited, and examples thereof include hydrogen sulfide (H ₂ S) gas and the like.

Although an embodiment of the present invention has been described above, the present invention is not limited to the above embodiment. Various modifications and changes can be made to the above-described embodiments without departing from the scope of the invention.

[Examples]

Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited by the examples.

[Example 1 to Example 5]

A glass plate containing substantially the same composition of the alkali-free glass was produced in the same manner by increasing the supply amount of hydrogen sulfide (H ₂ S) gas per unit time in the order of Examples 1 to 5. Examples 1 to 2 are comparative examples, and examples 3 to 5 are examples. Further, in Examples 1 to 5, the supply position of the hydrogen sulfide gas was set to the upstream side of the groove. Further, the supply amount of hydrogen sulfide gas in the system in Example 1 to 0Nm ³ / min, in embodiment 2, set 0.01Nm ³ / min, in Example 3 to 0.03Nm ³ / min, in Examples 4 to 0.06Nm ³ / min, in the embodiment is set to 5 0.1Nm ³ / min.

The alkali-free glass is represented by 59.5% by mass of SiO ₂ , 17% of Al ₂ O ₃ , 8% of B ₂ O ₃ , 3.3% of MgO, 4% of CaO, and 7.6% of SrO. 0.1% BaO, 0.1% ZrO ₂ , and MgO+CaO+SrO+BaO is 15%, and the remainder is an unavoidable impurity, and the total amount of the alkali metal oxide is 0.1% or less. For the measurement of the glass composition, a fluorescent X-ray analyzer (manufactured by RIGAKU Co., Ltd., ZSX100e) was used.

The glass plate obtained is processed to prepare a sample for measuring the sulfur concentration of the main body, a sample for measuring the sulfur concentration in the vicinity of the top surface, a sample for measuring the bending strength (thickness: 0.5 mm), and BHF (Buffered Hydrogen Fluoride). Sample for measurement of haze after treatment with hydrofluoric acid (thickness: 0.5 mm). The sample for measuring the sulfur concentration of the main body was produced by polishing the bottom surface and the top surface and cutting the center portion in the thickness direction of the glass sheet. The other sample for measurement was ground on the bottom surface and the top surface was not polished.

The sulfur concentration of the main body was measured by a fluorescent X-ray analyzer (manufactured by RIGAKU Co., Ltd., ZSX100e). Fluorescence X-ray analysis is suitable for high-precision determination of large-area regions compared to secondary ion mass spectrometry.

The sulfur concentration in the vicinity of the top surface was measured by a secondary ion mass spectrometer (manufactured by ULVAC, Adept 1010) while cutting the top surface. According to the measurement results, the sulfur concentration A (atoms/cm ³ ) of the glass at a position of a depth of 0.4 μm from the top surface and the sulfur concentration B of the glass at a position of a depth of 3 μm from the top surface were obtained (atoms/cm). ³ ) ratio (A/B).

The bending strength of the glass plate was measured by the ball ring method. The sample for measurement was placed on the annular ring with the top surface facing downward so that the tensile stress was applied to the top surface, and the ball placed on the center line of the ring was pressed from above by the center. Further, the cross-sectional shape of the ring is a circular shape having a diameter of 5 mm, and the diameter of the outer ring of the ring is set to 30 mm. Further, the diameter of the ball was set to 10 mm, and the moving speed of the ball was set to 10 mm/sec.

The damage load W (kN) when the sample for measurement having a thickness of 0.5 mm was cracked at the bent portion was measured, and converted into a bending strength S (GPa) based on the following formula (3).

S=-1.5584W ⁴ +4.8569W ³ -7.4492W ² +8.85W...(3)

(Where, W≦1.2kN)

Equation (3) is derived by simulation analysis using a computer. The analysis software system for simulation analysis uses "Solid Works Simulation" manufactured by Solid Works. Further, in the analysis, the Poisson's ratio of the glass plate was set to 0.23, and the Young's modulus of the glass plate was set to 77 GPa. These physical properties are physical property values of a usual alkali-free glass plate, but are also close to the physical property values of a usual soda lime glass plate (Poisson's ratio: 0.23, Young's modulus 72 GPa). Therefore, the formula (3) can be applied to both the alkali-free glass plate and the soda lime glass plate.

The haze value after the BHF treatment of the glass plate was measured by a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., NDH500). The sample for measurement was subjected to surface treatment by immersing in a solution of BHF at 25 ° C for 20 minutes, followed by washing and drying, and then measuring the haze. As the solution of BHF, a solution containing 0.5% by mass of HF, 36% by mass of NH ₄ F, and 63.5% by mass of water (ion-exchanged water) was used. In the washing, the sample for measurement after the BHF treatment was sequentially immersed in tap water, distilled water, and IPA (Isopropyl alcohol).

The measurement results of the sulfur concentration of the main body, the A/B in the vicinity of the top surface, the breaking load, the bending strength, and the haze are shown in Table 1. Since the variation of the breaking load and the bending strength is large, 30 measurement data are analyzed by the method according to the Weibo statistical analysis method (JIS R1625; 2010), and the bending strength is obtained by using the breaking load with a cumulative failure probability of 50%. .

[Example 6 to Example 10]

A glass plate containing a soda lime glass having substantially the same composition was produced in the same manner by increasing the supply amount of hydrogen sulfide (H ₂ S) gas per unit time in the order of Examples 6 to 10. Examples 6 to 7 are comparative examples, and examples 8 to 10 are examples. Further, in Examples 6 to 10, the supply position of the hydrogen sulfide gas was set to the upstream side of the groove. Further, the supply amount of hydrogen sulfide gas in the system of Example 6 is set 0Nm ³ / min, in Example 7 to 0.01Nm ³ / min, in the embodiment to 8 0.05Nm ³ / min, as in Example 9 to 0.1Nm ³ / min, as in Example 10 to 0.2Nm ³ / min.

The soda lime glass is represented by 71.5% of SiO ₂ , 1.8% of Al ₂ O ₃ , 8.5% of CaO, 4.0% of MgO, 13.0% of Na ₂ O, and 0.5% of K ₂ based on the mass % of the oxide. O, 0.1% Fe ₂ O ₃ , 0.05% TiO ₂ , 0.2% SO ₃ , and the remainder is an unavoidable impurity. For the measurement of the glass composition, a fluorescent X-ray analyzer (manufactured by RIGAKU Co., Ltd., ZSX100e) was used.

In order to eliminate the influence of the sulfate formed in the slow cooling step, only the bottom surface is polished, and the sample for measurement of the sulfur concentration in the vicinity of the top surface and the sample for measurement of the bending strength (thickness: 0.5 mm) are prepared. And a sample for measuring the haze after the BHF treatment (thickness: 0.5 mm). The sample for measuring the sulfur concentration of the main body was produced by polishing the bottom surface and the top surface and cutting the center portion in the thickness direction of the glass sheet. The other sample for measurement was ground on the bottom surface and the top surface was not polished.

The measurement results of the sulfur concentration of the main body, the A/B in the vicinity of the top surface, the breaking load, the bending strength, and the haze are shown in Table 1. Further, the measurement methods were the same as in Examples 1 to 5.

The present application is based on Japanese Patent Application No. 2012-089280, filed on Apr.

Claims (10)

A glass plate formed by flowing molten glass continuously supplied onto molten metal in a molten metal tank onto the molten metal, wherein the glass plate is exposed to a reducing environment from the molten metal tank. The concentration of sulfur in the glass at a position where the depth of the main surface is 0.3 to 0.5 μm is greater than or equal to the sulfur concentration of the glass at a position of 3 μm from the main surface. The glass plate of claim 1, wherein the glass of the glass plate is an alkali-free glass. The glass plate of claim 2, wherein the plate thickness is 0.2 to 0.7 mm, and the bending strength when the tensile stress is applied to the main surface is 4 GPa or more. The glass plate of claim 2 or 3, wherein the buffered hydrofluoric acid solution containing 0.5% by mass of hydrofluoric acid (HF), 36% by mass of ammonium fluoride (NH ₄ F), and 63.5% by mass of water at 25 ° C The haze value after immersion for 20 minutes was 1% or less. The glass plate according to any one of claims 2 to 4, wherein the alkali-free glass contains 50 to 66% of SiO ₂ , 10.5 to 24% of Al ₂ O ₃ , 0 to 12 by mass% of oxide. % B ₂ O ₃ , 0~8% MgO, 0~14.5% CaO, 0~24% SrO, 0~13.5% BaO, 0~5% ZrO ₂ , 0~3% SnO, Further, MgO+CaO+SrO+BaO is 9 to 29.5%, and the total amount of the alkali metal oxide is 0.1% or less. The glass plate of claim 5, wherein the alkali-free glass comprises 58 to 66% of SiO ₂ , 15 to 22% of Al ₂ O ₃ , and 5 to 12% of B ₂ O ₃ based on the mass % of the oxide. 0~8% of MgO, 0~9% of CaO, 3~12.5% of SrO, 0~2% of BaO, 0~1% of SnO, and MgO+CaO+SrO+BaO is 9~18%, The total amount of the alkali metal oxide is 0.1% or less. The glass plate of claim 1, wherein the glass of the glass plate is soda lime glass. The glass plate of claim 7, wherein the plate thickness is 0.2 to 0.7 mm, and the bending strength when the tensile stress is applied to the main surface is 2.5 GPa or more. A glass plate according to claim 7 or 8, which comprises a buffered hydrofluoric acid solution containing 0.5% by mass of hydrofluoric acid (HF), 36% by mass of ammonium fluoride (NH ₄ F), and 63.5% by mass of water at 25 ° C. The haze value after immersion for 20 minutes was 3% or less. The glass plate according to any one of claims 7 to 9, wherein the soda lime glass contains 65 to 75% of SiO ₂ , 0 to 13% of Al ₂ O ₃ , 0 to 15 by mass% of oxide. % CaO, 0~15% MgO, 10-20% Na ₂ O, 0-10% K ₂ O, 0~5% Li ₂ O, 0~3% Fe ₂ O ₃ , 0~ 5% of TiO ₂ , 0 to 3% of CeO ₂ , 0 to 10% of BaO, 0 to 5% of SrO, 0 to 5% of B ₂ O ₃ , 0 to 5% of ZnO, 0 to 10% ZrO ₂ , 0 to 3% of SnO ₂ , and 0 to 0.5% of SO ₃ .