CN115784575A

CN115784575A - Float glass manufacturing method and float glass

Info

Publication number: CN115784575A
Application number: CN202211323853.XA
Authority: CN
Inventors: 井上俊二; 泷口哲史; 山崎健史; 中野胜之; 西野琢也; 水野润一
Original assignee: Asahi Glass Co Ltd
Current assignee: AGC Inc
Priority date: 2017-11-27
Filing date: 2018-11-16
Publication date: 2023-03-14
Also published as: CN110028228B; JP2019094245A; KR20190062198A; CN110028228A

Abstract

The present invention relates to a float glass production method and float glass. The invention provides a method for manufacturing float glass, which can obtain large float glass with small thickness deviation. A float glass production method in which molten glass is continuously supplied onto molten metal in a bath, the molten glass is formed into a glass ribbon while being caused to flow over the molten metal, and the glass is conveyed in a slow cooling furnace while being conveyedCooling the glass ribbon slowly at one side of the glass ribbon, wherein the viscosity at the center of the glass ribbon in the width direction on the molten metal is 10 ^4.5 dPa s or more and 10 ^7.5 When a region of dPa · s or less is referred to as a forming region, the following formula (1) is satisfied where D0 (unit: mm) is a depth of the molten metal in the forming region and V (unit: m/min) is a conveying speed of the glass ribbon in the slow cooling furnace: d0 is greater than or equal to 1.0 XV +30 \8230; (1).

Description

Float glass manufacturing method and float glass

The application is a divisional application of Chinese patent application with application number 201811365412.X, application date 2018, month 11 and 16.

Technical Field

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

Background

The thickness variation in the entire surface of a glass substrate for a Flat Panel Display (FPD) affects the defocus of an exposure machine in a photolithography process. Glass substrates for FPDs, particularly glass substrates for Liquid Crystal Displays (LCDs), are strongly required to have a variation in plate thickness, for example, within a range of 1500mm, the variation in plate thickness is required to be 20 μm or less. The thickness deviation is a difference between the maximum value of the thickness and the minimum value of the thickness.

As a method for reducing the thickness deviation, patent document 1 proposes the following technique: the heater zone of the float furnace is divided along the flow direction and the width direction of the glass ribbon, and a plurality of heaters are provided in each section, and the plurality of heaters are controlled in each section.

Documents of the prior art

Patent document

Patent document 1: japanese laid-open patent publication No. 2012-1398

Disclosure of Invention

Problems to be solved by the invention

In recent years, there has been an increasing demand for increasing the size of FPDs, and an increase in the size of glass substrates for FPDs has been desired. However, it is difficult to achieve both an increase in size of the glass substrate and a reduction in thickness variation.

The present invention has been made in view of the above problems, and a main object thereof is to provide a method for manufacturing a float glass, which can obtain a large float glass having a small variation in thickness.

Means for solving the problems

In accordance with one aspect of the present invention,

provided is a float glass production method in which molten glass is continuously supplied onto molten metal in a bath, the molten glass is formed into a glass ribbon while being caused to flow over the molten metal, and the glass ribbon is slowly cooled while being conveyed in a slow cooling furnace, characterized in that,

the viscosity at the widthwise center of the glass ribbon on the molten metal was 10 ^4.5 dPa · s or more and 10 ^7.5 When the region of dPas or less is called a molding region,

when the depth of the molten metal in the forming region is D0 (unit: mm) and the conveying speed of the glass ribbon in the slow cooling furnace is V (unit: m/min), the following formula (1) is satisfied:

D0≥1.0×V+30…(1)。

effects of the invention

According to one embodiment of the present invention, a method for manufacturing float glass is provided, which can obtain large float glass having a small variation in thickness.

Drawings

FIG. 1 is a cross-sectional view of a float glass manufacturing apparatus according to one embodiment.

FIG. 2 is a cross-sectional view of the float glass manufacturing apparatus taken along line II-II of FIG. 1.

Fig. 3 is a plan view showing a bath, a glass ribbon, and an upper roller according to an embodiment.

Fig. 4 is a sectional view showing the depth of molten metal according to example 1.

FIG. 5 is a plan view showing a bath, a glass ribbon, an upper roller and a barrier wall according to a modification.

Fig. 6 is a sectional view of the barrier rib shown in fig. 5.

Fig. 7 is a plan view showing the arrangement of a heater control section according to an embodiment.

Fig. 8 is a graph showing the relationship between the conveying speed V and the depth D in examples 1 to 5 and comparative examples 1 to 3.

Reference numerals

10. Float glass manufacturing device

20. Bath tub

21. Metal shell

22. Side brick

23. Bottom brick

25. Cooling nozzle

30. Top board

40. Heating device

41. Heater control column

42. Heater control section

45. Parting line

46. Dividing line

50. Controller

60. Upper roll

70. Slow cooling furnace

Detailed Description

Hereinafter, specific embodiments of the present invention will be described with reference to the drawings. In the drawings, the same or corresponding components are given the same or corresponding reference numerals, and description thereof will be omitted.

(overview of float glass production apparatus)

FIG. 1 is a cross-sectional view of a float glass manufacturing apparatus according to one embodiment. FIG. 2 is a cross-sectional view of the float glass manufacturing apparatus taken along line II-II of FIG. 1. In fig. 1 and 2, an illustration of the upper roller 60 shown in fig. 3 is omitted. Fig. 3 is a plan view showing a bath, a glass ribbon, and an upper roller according to an embodiment. In each drawing, the X direction is the flow direction of the glass ribbon 6, the Y direction is the width direction of the glass ribbon 6, and the Z direction is the vertical direction. The X direction, the Y direction, and the Z direction are directions perpendicular to each other.

The float glass manufacturing apparatus 10 has a bath 20, and the bath 20 contains molten metal 2 floating molten glass 4. As the molten metal 2, molten tin or a molten tin alloy is typically used. The molten glass 4 is continuously supplied onto the molten metal 2 contained in the bath 20, and is formed into a plate-like glass ribbon 6 while flowing from the upstream side to the downstream side on the molten metal 2. The glass ribbon 6 is gradually cooled and hardened while flowing in the direction of arrow a above the liquid surface of the molten metal 2. The glass ribbon 6 is lifted from the molten metal 2 in a downstream area of the bath 20, and then gradually cooled while being conveyed from the inlet to the outlet of the slow cooling furnace 70 in the slow cooling furnace 70. The glass ribbon 6 cooled slowly in the slow cooling furnace 70 is cut into a predetermined size, whereby a glass sheet (float glass) is manufactured.

The float glass manufacturing apparatus 10 includes: a ceiling plate 30 provided above the bath tub 20, a plurality of heaters 40 suspended on the ceiling plate 30, and a plurality of controllers 50 controlling the plurality of heaters 40. The plurality of heaters 40 heat the glass ribbon 6 passing thereunder under the control of the plurality of controllers 50. As each heater 40, for example, an electric heater that performs energization heating is used. The shape of each heater 40 is not particularly limited, and may be, for example, a rod shape. The temperature distribution of the glass ribbon 6 is controlled by controlling the amount of heat generated by each heater 40. The plurality of controllers 50 are devices that control the amount of heat generation of the plurality of heaters 40. Each controller 50 is constituted by a microcomputer or the like.

The float glass manufacturing apparatus 10 has a plurality of pairs of upper rollers 60 that are provided spaced apart from each other along the flow direction of the glass ribbon 6 and support both width-direction end portions of the glass ribbon 6 (refer to fig. 3). The pair of upper rollers 60 supports both ends in the width direction of the glass ribbon 6, thereby suppressing the width of the glass ribbon 6 from being narrowed by surface tension. Each upper roller 60 is composed of a disc-shaped upper roller body 61 that supports the end portion of the glass ribbon 6 in the width direction, and a rotating shaft 62 connected to the upper roller body 61. The disc-shaped upper roller body 61 is provided coaxially with the rotation shaft 62. When the rotary shaft 62 is rotationally driven by a driving device such as a motor, the upper roller body 61 rotates to feed the glass ribbon 6 to the downstream side.

(bath tub)

As shown in fig. 3, the bath 20 includes, in order from the downstream end to the upstream side: a narrow region A1 in which the width direction dimension of the bath 20 is constant, an intermediate region A2 in which the width direction dimension of the bath 20 gradually increases, and a wide region A3 in which the width direction dimension of the bath 20 is larger than the narrow region A1 and is constant. The X-direction dimension X1 of the wide area A3 is, for example, 30% to 80% of the X-direction dimension X0 of the molten metal 2 contained in the bath 20.

The plurality of pairs of upper rollers 60 support both ends of the glass ribbon 6 in the width direction in the wide region A3. The contact points of the respective upper roller bodies 61 with the glass ribbon 6 are provided spaced apart from each other between the upstream end of the forming area A4 and the downstream end of the forming area A4. The forming region A4 is a region where the viscosity at the center in the width direction (center in the Y direction) of the glass ribbon 6 is 10 ^4.5 dPa · s or more and 10 ^7.5 A region of dPa · s or less.

As shown in fig. 2, the bath 20 includes: a box-shaped metal case 21, a plurality of side bricks 22 placed on the bottom surface of the metal case 21 and contacting the side surfaces of the molten metal 2, and a plurality of bottom bricks 23 placed on the bottom surface of the metal case 21 and contacting the lower surface of the molten metal 2. The side bricks 22 are arranged adjacent to the side surface of the metal case 21, and the bottom bricks 23 are arranged inside the side bricks 22 in the X direction and the Y direction.

Seams 24 are formed between the bottom bricks 23 adjacent in the Y direction. The seam 24 is a gap. It is difficult to prevent the molten metal 2 from flowing into the joint 24. The molten metal 2 flowing into the joint 24 reaches the bottom surface of the metal shell 21.

In order to suppress the reaction between the metal shell 21 and the molten metal 2, a cooling nozzle 25 for blowing a cooling gas such as air to the lower surface of the metal shell 21 is provided below the metal shell 21. The cooling nozzle 25 blows a cooling gas in the direction of the arrow B (upward). This can reduce the temperature of the metal shell 21 to the melting point of the molten metal 2 or less, and can suppress the reaction between the molten metal 2 and the metal shell 21.

Fig. 4 is a sectional view showing the depth of molten metal according to example 1. In fig. 4, the lower portions of the metal case 21 and the bottom block 23 are omitted. In the present specification, the depth D of the molten metal 2 is measured between the glass ribbon 6 and the side bricks 22 (more specifically, the outer side in the width direction of the glass ribbon 6 and the inner side in the width direction of the side bricks 22) as shown in fig. 2, which is the distance from the liquid surface (upper surface) of the molten metal 2 to the upper surface of the bottom bricks 23.

As shown in fig. 4, the depth D of the molten metal 2 may vary from the upstream end of the molten metal 2 to the downstream end of the molten metal 2. The depth D of the molten metal 2 is set as shallow as possible. This is to reduce the manufacturing cost of the float glass by suppressing the amount of the molten metal 2 to the minimum necessary amount.

In the present embodiment, the depth D0 of the molten metal 2 in the forming region A4 is set based on the conveying speed V of the glass ribbon 6 in the annealing furnace 70 (see fig. 4), and is set so as to satisfy the following expression (1).

D0≥1.0×V+30…(1)

In the above formula (1), D0 is in mm, and V is in m/min. V is set according to the thickness of the float glass, and is, for example, 3 m/min to 11 m/min. D0 is, for example, 35mm to 60mm. Preferably, V is from 4 to 8 m/min and D0 is from 35 to 50mm. D0 is more preferably 35mm to 45mm.

When the above equation (1) is satisfied, the flow velocity of the molten metal 2 indicated by the arrow C in fig. 3 in the forming region A4 where the size and shape of the glass ribbon 6 are adjusted can be reduced. As a result, deformation of the size and shape of the glass ribbon 6 due to the backflow of the molten metal 2 can be suppressed (collapse 12428).

First, the reason why the reverse flow of the molten metal 2 indicated by the arrow C in fig. 3 occurs will be described. While the glass ribbon 6 is conveyed at the conveying speed V in the annealing furnace 70, the glass ribbon 6 flows on the molten metal 2 toward the annealing furnace 70 at the same speed as the conveying speed V at a position downstream of the forming zone A4. At this time, the molten metal 2 directly below the glass ribbon 6 is dragged by the glass ribbon 6 and flows into the annealing furnace 70 at the same speed as the glass ribbon 6. The flow of molten metal 2 is blocked at the downstream end of the bath 20, reversing direction. As a result, the molten metal 2 flows backward outside the glass ribbon 6 in the width direction.

Next, the volume flow rate Q of the molten metal 2 flowing back will be described. The reverse flow of the molten metal 2 is generated by the glass ribbon 6 dragging the molten metal 2 as described above. Therefore, the volume flow rate Q is proportional to the conveyance speed V of the glass ribbon 6 and the width-direction dimension of the glass ribbon 6. The volume flow Q is hardly dependent on the depth D of the molten metal 2. This is because the portion of the molten metal 2 dragged by the glass ribbon 6 is only the portion near the glass ribbon 6.

Next, the flow rate u of the molten metal 2 flowing back will be described. Generally, the product of the flow velocity u and the sectional area SA is the volume flow Q (= u × SA). Here, Q has the unit m ³ The unit of u is m/s, the unit of SA is m ² . The cross-sectional area SA of the flow path of the molten metal 2 flowing back is 2 times (SA = D × W × 2 × 10) the product of the depth D (see fig. 2) of the molten metal 2 and the distance W (see fig. 2) between the glass ribbon 6 and the side block 22 in the Y direction ^-3 ) And (4) showing. In the formula, D is represented by mm, and W is represented by m. The product of D and W multiplied by 2 is because the flow paths for the reverse flows of the molten metal 2 are provided on both sides so as to sandwich the glass ribbon 6 in the width direction. Thus, a volume flow rate Q = u × D × W × 2 × 10 was obtained ^-3 . On the other hand, the volume flow rate Q is proportional to the conveyance speed V of the glass ribbon 6 as described above. Therefore, it can be seen that the flow rate u is proportional to V/D with W being constant.

The present inventors have paid attention to the fact that the flow velocity u is proportional to V/D, and have considered that the relationship between V and D for suppressing deformation of the size and shape of the glass ribbon 6 due to the backflow of the molten metal 2 can be expressed by a linear equation, and have obtained the relational expression of the above expression (1) by experiments or the like. In the column of examples, specific experiments are described.

When the above equation (1) is satisfied, as described above, the flow velocity u of the backward flow of the molten metal 2 indicated by the arrow C in fig. 3 in the forming region A4 where the size and shape of the glass ribbon 6 are adjusted can be reduced. As a result, deformation of the size and shape of the glass ribbon 6 due to the backflow of the molten metal 2 can be suppressed, and a large float glass with small variation in the thickness can be obtained.

This effect is remarkably obtained as the width-directional dimension of the glass ribbon 6 is larger. This is because the back-flowing volume flow rate Q of the molten metal 2 is proportional to the width-direction dimension of the glass ribbon 6. According to this embodiment, it is possible to obtain a rectangular float glass in a plan view having a longitudinal dimension of 2100mm or more, a lateral dimension of 2200mm or more, and an average plate thickness of 0.75mm or less, and the difference between the maximum value and the minimum value of the plate thickness in the entire surface of the float glass is 12 μm or less. Here, the vertical dimension is a dimension in a short side direction of the rectangular float glass in a plan view, and the horizontal dimension is a dimension in a long side direction of the rectangular float glass in a plan view. The plan view is viewed from the Z direction in fig. 3 and the like.

In the present embodiment, the depth D1 (see fig. 4) of the molten metal 2 in the HOT zone A5 (see fig. 4) is, for example, 1.6 times or more and 2.0 times or less the depth D0 of the molten metal 2 in the forming zone A4. HOT zone A5 is the region where molten glass 4 spreads on molten metal 2 under the influence of gravity. When D1 is 1.6 times or more D0, contact between the molten glass 4 and the bottom block 23 due to injection of the molten glass 4 can be suppressed. In addition, when D1 is 2.0 times or less D0, the use of the wasted molten metal 2 can be suppressed, and the manufacturing cost of the float glass can be reduced.

In the present embodiment, the depth D2 (refer to fig. 4) of the molten metal 2 at the upstream end of the narrow region A1 (refer to fig. 4) is, for example, 2.0 times or more and 2.5 times or less the depth D0 of the molten metal 2 in the forming region A4. When D2 is 2.0 times or more D0, the depth D of the molten metal 2 having high thermal conductivity is increased, and the thickness of the bottom block 23 having low thermal conductivity is decreased, so that the glass ribbon 6 is easily cooled and easily hardened by the cooling nozzle 25 (see fig. 1 and 2) provided below the bottom block 23. In addition, when D2 is 2.5 times or less D0, the use of the wasted molten metal 2 can be suppressed, and the manufacturing cost of the float glass can be reduced.

Fig. 5 is a plan view showing a bath, a glass ribbon, an upper roller, and a barrier wall according to a modification. Fig. 6 is a sectional view of the barrier rib shown in fig. 5. The bath 20 shown in fig. 5 and 6 differs from the bath 20 shown in fig. 4 in that the barrier 27 is detachably mounted. Hereinafter, the difference will be mainly explained.

The barrier wall 27 blocks the flow of the molten metal 2 on the widthwise outer side of the glass ribbon 6 on the molten metal 2 and reduces the flow rate of the reverse flow of the molten metal 2 in the forming zone A4. As a result, deformation of the size and shape of the glass ribbon 6 due to the backflow of the molten metal 2 can be further suppressed, and a large float glass with small variation in sheet thickness can be obtained. The barrier wall 27 may be disposed downstream of the forming area A4 in the wide area A3 as shown in fig. 5.

The barrier ribs 27 are provided over the entire Z direction of the molten metal 2 from the upper surface of the bottom bricks 23 to the liquid surface of the molten metal 2 as shown in fig. 6, and may be provided so as to protrude upward from the liquid surface of the molten metal 2. The barrier 27 may be provided only in a part of the molten metal 2 in the Z direction. In this case, the barrier ribs 27 may be disposed in contact with the upper surface of the bottom brick 23. This is because the reverse flow of the molten metal 2 is easily generated in a region away from the glass ribbon 6 dragging the molten metal 2 and is easily generated in the vicinity of the upper surface of the bottom brick 23.

The barrier ribs 27 are made of, for example, carbon, and are immersed in the molten metal 2. In the case where the density of the barrier ribs 27 is lower than that of the molten metal 2, a pressing member 28 (refer to fig. 6) that presses the barrier ribs 27 so that the barrier ribs 27 do not float up due to a density difference may be fixed on the side bricks 22.

(Heater)

Fig. 7 is a plan view showing the arrangement of a heater control section according to an embodiment. Fig. 7 illustrates the arrangement of the heater control sections in the wide area A3, and the arrangement of the heater control sections in the middle area A2 and the narrow area A1 is not illustrated. The heater 40 may be provided not only in the wide area A3 but also in the intermediate area A2 and the narrow area A1.

As shown in fig. 7, the heater area where the plurality of heaters 40 are provided is divided into a plurality of heater control columns 41 in the X direction. Each heater control column 41 is divided into a plurality of heater control sections 42 in the Y direction. Note that the number of the heater control columns 41 is not limited to the number shown in fig. 7. In addition, the number of heater control sections 42 in each heater control column 41 is not limited to the number shown in fig. 7.

Each of the heater control sections 42 is provided with a plurality of heaters 40, and is collectively controlled by a corresponding one of the controllers 50 (see fig. 1). Thereby, the number of controllers 50 can be reduced. The plurality of heaters 40 provided in one heater control section 42 are collectively controlled by one corresponding controller 50 so that the respective heat generation amounts are substantially the same.

Two heater control rows 41 adjacent in the X direction are divided by one dividing line 45. The dividing line 45 is located substantially at the center between the actual heaters 40 adjacent in the X direction. On the other hand, two heater control sections 42 adjacent in the Y direction are divided by one dividing line 46. The dividing line 46 is located at substantially the center between the actual heaters 40 adjacent in the Y direction.

Incidentally, in one heater control row 41, when the heat generation amounts per unit area are different in two heater control sections 42 adjacent in the Y direction, a sharp temperature change occurs along the Y direction in the vicinity of the dividing line 46.

Therefore, in the present embodiment, at least one dividing line 45, the dividing line 46 of the upstream heater control column 41 and the dividing line 46 of the downstream heater control column 41 are provided so as to be discontinuous at one or more places and shifted at one or more places. For example, at the m-th dividing line 45-m from the upstream side (left side in fig. 7), the dividing line 46 of the m-th heater control column 41-m from the upstream side and the dividing line 46 of the m + 1-th heater control column 41-m +1 from the upstream side are provided so as to be discontinuous at one or more places and shifted at one or more places. Here, m is at least one natural number of 1 or more, and for example, in fig. 7, is an arbitrary natural number of 1 or more and 6 or less.

In the glass ribbon 6, a portion passing below the dividing line 46 where the temperature change is rapid in the m-th heater control row 41-m passes below the heater control section 42 where the temperature change is slow in the m + 1-th heater control row 41-m + 1. This can suppress temperature unevenness in the Y direction of the glass ribbon 6, and can reduce thickness unevenness in the Y direction of the glass ribbon 6.

In the present embodiment, at least one dividing line 45 in the wide area A3 in the Z direction, the dividing line 46 of the upstream heater control column 41 and the dividing line 46 of the downstream heater control column 41 are provided so as to be discontinuous at one or more points and shifted at one or more points. This is because the wide region A3 is higher in temperature than the intermediate region A2 and the narrow region A1, and the size and shape of the glass ribbon 6 are adjusted in the wide region A3. In the intermediate region A2 and the narrow region A1, the viscosity of the glass ribbon 6 is high, and therefore, it is difficult to adjust the size and shape of the glass ribbon 6.

In the present embodiment, at least one dividing line 45 in the molding zone A4 in the Z direction, the dividing line 46 of the upstream heater control row 41 and the dividing line 46 of the downstream heater control row 41 are provided so as to be discontinuous at one or more points and shifted at one or more points. This is because the size and shape of the glass ribbon 6 are adjusted by using the upper roller 60 in the forming area A4 also in the wide area A3.

The heater control lines 41 may be arranged so that the plurality of dividing lines 46 are line-symmetrical about the Y-direction center line 20L of the bath 20. This makes it possible to make the temperature distribution of the molten metal 2 and the temperature distribution of the glass ribbon 6 line-symmetrical about the Y-direction center line 20L of the bath 20. As a result, the control of the thickness distribution of the glass ribbon 6 is facilitated.

(float glass)

The float glass has a rectangular shape in plan view, and has a longitudinal dimension of 2100mm or more, a lateral dimension of 2200mm or more, and an average plate thickness of 0.75mm or less. The difference between the maximum value and the minimum value of the thickness of the float glass in the whole surface is less than 12 μm. When the float glass is used for a glass substrate for FPD, the variation in the thickness of the glass substrate over the entire surface of a large area can be reduced, and the defocus of the exposure apparatus can be suppressed. The float glass having a rectangular shape in a plan view includes float glass having corners ground by corner grinding stones. The ground portion is referred to as a chamfered portion, and the size of the chamfered portion is, for example, several mm.

The float glass preferably has a longitudinal dimension of 2900mm or more and a transverse dimension of 3000mm or more.

The average thickness of the float glass is preferably 0.45mm or less.

The float glass is composed of, for example, alkali-free glass containing, in mass% on an oxide basis: siO 2 ₂ ：54％～66％、Al ₂ O ₃ ：10％～23％、B ₂ O ₃ :0% -12%, mgO:0% -12%, caO:0% -15%, srO:0% -16%, baO:0% -15%, mgO + CaO + SrO + BaO:8 to 26 percent. Here, "MgO + CaO + SrO + BaO" refers to the total content of MgO, caO, srO, and BaO. Further, "alkali-free glass" means Li ₂ O、Na ₂ O and K ₂ The total content of alkali metal oxides such as O is less than 0.1 mass%. The alkali-free glass is preferably B in mass% based on oxides ₂ O ₃ The content of (B) is 5% or less.

Examples

The present invention will be further described below with reference to examples and comparative examples. The present invention is not limited to these descriptions. In the examples and comparative examples, the longitudinal direction corresponds to the X direction and the transverse direction corresponds to the Y direction.

Fig. 8 is a graph showing the relationship between the conveying speed V and the depth D in examples 1 to 5 and comparative examples 1 to 3. The experimental conditions and experimental results of examples 1 to 5 and comparative examples 1 to 3 are shown in table 1 and fig. 8. The chemical compositions of the glass materials 1 to 3 used in examples 1 to 5 and comparative examples 1 to 3 are shown in table 2.

TABLE 1

TABLE 2

Composition (I)	Glass material 1	Glass material 2	Glass material 3
				SiO ₂ (mass%)	61.0	60.0	64.4
Al ₂ O ₃ (mass%)	20.0	17.0	8.0
				B ₂ O ₃ (mass%)	1.5	8.0	0.0
MgO (% by mass)	5.5	3.0	10.5
				CaO (mass%)	4.5	4.0	0.05
SrO (mass%)	7.0	8.0	0.0
				BaO (% by mass)	0.0	0.0	0.0
K ₂ O (mass%)	0.0	0.0	4.0
				ZrO ₂ (mass%)	0.0	0.0	0.5
Na ₂ O (mass%)	0.0	0.0	12.5
				MgO + CaO + SrO + BaO (% by mass)	17.0	23.0	10.55

[ examples 1 to 5]

In example 1, a glass ribbon 6 having a width dimension of 4000mm or more was produced using the float glass production apparatus 10 having the bath 20 shown in fig. 3 and 4. As a glass material as a raw material of the glass ribbon, glass material 1 shown in table 2 was used. The depth D0 in the molten tin forming region A4 as the molten metal 2 was set to 38mm. The conveying speed V of the glass ribbon 6 in the annealing furnace 70 was set to 4.2 m/min.

Float glass having a transverse dimension of 2500mm and float glass having a transverse dimension of 3500mm were cut out from the produced glass ribbon 6. Each float glass was cut out symmetrically in the left-right direction about the center line in the width direction of the glass ribbon. The average thickness of each float glass was 0.50mm.

Float glass was obtained under the same conditions as in example 1 except that in examples 2 to 4, the amount of molten tin used was increased or decreased, respectively, to change the depth D0 in the molding region A4 of the molten tin to 37mm, 39mm, and 40mm, and the conveying speed V of the glass ribbon 6 in the annealing furnace 70 was increased to 4.9 m/min, 5.3 m/min, and 6.7 m/min.

In example 5, float glass was obtained under the same conditions as in example 1 except that the glass material 3 shown in table 2 was used as the glass material, the amount of molten tin used was increased to change the depth D0 in the forming region A4 of the molten tin to 45mm, and the conveying speed V of the glass ribbon 6 in the annealing furnace 70 was increased to 10 m/min.

Comparative examples 1 to 3

In comparative example 1, float glass was obtained under the same conditions as in example 1, except that the amount of molten tin used was reduced and the depth D0 in the forming region A4 of the molten tin was changed to 33mm, and the conveying speed V of the glass ribbon 6 in the lehr 70 was increased and changed to 4.9 m/min.

In comparative example 2, float glass was obtained under the same conditions as in example 1 except that the glass material 2 shown in table 2 was used as the glass material, the amount of molten tin used was reduced, the depth D0 in the molding region A4 of the molten tin was changed to 35.5mm, and the conveying speed V of the glass ribbon 6 in the slow cooling furnace 70 was increased, and was changed to 7.6 m/min.

In comparative example 3, float glass was obtained under the same conditions as in example 1 except that the glass material 3 shown in Table 2 was used as the glass material and the conveying speed V of the glass ribbon 6 in the slow cooling furnace 70 was increased to 10.3 m/min.

[ conclusion ]

As is clear from table 1 and fig. 8, in examples 1 to 5, unlike comparative examples 1 to 3, since the condition experiment satisfying the above formula (1) was performed, a large float glass having a small variation in sheet thickness was obtained. Specifically, in the float glass having a lateral dimension of 2500mm and the float glass having a lateral dimension of 3500mm, the deviation in plate thickness is 12 μm or less.

Although the embodiments of the float glass production method and the float glass have been described above, the present invention is not limited to the above embodiments, and various modifications and improvements can be made within the scope of the present invention described in the claims.

Claims

1. A float glass having a vertical dimension of 2100mm or more, a lateral dimension of 2200mm or more, and an average plate thickness of 0.75mm or less, which is rectangular in a plan view,

the difference between the maximum value and the minimum value of the thickness of the float glass in the whole surface is less than 12 μm.

2. The float glass of claim 1,

the float glass has a longitudinal dimension of 2900mm or more and a transverse dimension of 3000mm or more.

3. The float glass of claim 1,

the average plate thickness is 0.45mm or less.

4. The float glass of claim 2,

the average plate thickness is 0.45mm or less.

5. The float glass according to any one of claims 1 to 4, wherein the float glass is composed of an alkali-free glass containing, in mass% on an oxide basis:

SiO ₂ ：54％～66％、

Al ₂ O ₃ ：10％～23％、

B ₂ O ₃ ：0％～12％、

MgO：0％～12％、

CaO：0％～15％、

SrO：0％～16％、

BaO:0% to 15%, and

MgO+CaO+SrO+BaO：8％～26％。

6. the float glass of claim 5,

b of the alkali-free glass expressed in mass% on an oxide basis ₂ O ₃ The content of (B) is 5% or less.