JP2019094245A - Float glass production method and float glass - Google Patents

Abstract

To provide a float glass production method capable of producing a large size float glass with low plate thickness deviation.SOLUTION: In the float glass production method, which continuously provides the molten glass on a molten metal in a bath tub, and molds it into a glass ribbon while flowing the molten glass on the molten metal, and which gradually cools the glass ribbon while carrying it in a slow cooling furnace, the formation D0≥1.0×V+30...(1) is satisfied, where a region where viscosity on a center in a width direction of the glass ribbon on the molten metal of 10dPa s or more, and 10dPa s or less is a mold region and a depth of the molten metal in the mold region is D0(mm) and transportation speed of the glass ribbon in the slow cooling furnace is V(m/min).SELECTED DRAWING: Figure 8

Description

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

  The thickness deviation over the entire surface of the glass substrate for flat panel display (FPD) affects the defocus of the exposure machine in the photolithography process. Glass substrates for FPDs, in particular glass substrates for liquid crystal displays (LCDs), have strict requirements for thickness deviation, and are required to be, for example, 20 μm or less in the range of 1500 mm. The thickness deviation is the difference between the maximum thickness and the minimum thickness.

  As a method of reducing thickness deviation, Patent Document 1 divides the heater area of the float bath in the flow direction and width direction of the glass ribbon, provides a plurality of heaters in each section, and controls the plurality of heaters for each section Technology has been proposed.

JP 2012-1398 A

  In recent years, the demand for enlargement of FPDs is increasing, and enlargement of glass substrates for FPDs is desired. However, it is not easy to simultaneously increase the size of the glass substrate and reduce the thickness deviation.

  This invention is made in view of the said subject, Comprising: It aims mainly at provision of the float glass manufacturing method which is large and can obtain float glass with a small board thickness deviation.

According to one aspect of the invention:
Molten glass is continuously supplied onto molten metal in a bath, formed into a glass ribbon while flowing the molten glass on the molten metal, and floated to be gradually cooled while conveying the glass ribbon in a lehr. A glass manufacturing method,
When a region having a viscosity of 10 ^4.5 dPa · s to 10 ^7.5 dPa · s at the center in the width direction of the glass ribbon on the molten metal is referred to as a forming region,
The depth of the molten metal in the forming region is D0 (unit: mm), and the transport speed of the glass ribbon in the slow cooling furnace is V (unit: m / min), and the following formula (1) is satisfied. A method of making float glass is provided.
D0 ≧ 1.0 × V + 30 (1)
Is provided.

  According to one aspect of the present invention, a float glass manufacturing method is provided in which a large float glass having a small thickness deviation is obtained.

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. FIG. 3 is a plan view of a bath, a glass ribbon and a top roll according to one embodiment. FIG. 4 is a cross-sectional view showing the depth of the molten metal according to the first embodiment. FIG. 5 is a plan view showing a bathtub, a glass ribbon, a top roll and a barrier according to a modification. 6 is a cross-sectional view of the barrier shown in FIG. FIG. 7 is a plan view showing the arrangement of heater control sections according to one embodiment. FIG. 8 is a view showing the relationship between the transport speed V and the depth D in Examples 1 to 5 and Comparative Examples 1 to 3.

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

(Outline of float glass manufacturing equipment)
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. In FIG. 1 and FIG. 2, the top roll 60 shown in FIG. 3 is not shown. FIG. 3 is a plan view of a bath, a glass ribbon and a top roll according to one 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 for containing the molten metal 2 on which the molten glass 4 floats. Typically, molten tin or a molten tin alloy is used as the molten metal 2. 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 gradually cools and hardens while flowing in the direction of arrow A above the liquid surface of the molten metal 2. The glass ribbon 6 is pulled up from the molten metal 2 in the downstream region of the bath 20 and then gradually cooled while being transported in the lehr 70 from the inlet to the outlet of the lehr 70. A glass plate (float glass) is manufactured by cutting the glass ribbon 6 annealed in the lehr 70 to a predetermined size.

  The float glass manufacturing apparatus 10 has a ceiling 30 provided above the bathtub 20, a plurality of heaters 40 suspended from the ceiling 30, and a plurality of controllers 50 for controlling the plurality of heaters 40. The plurality of heaters 40 heat the glass ribbon 6 passing below under the control of the plurality of controllers 50. For each heater 40, for example, an electric heater that is energized and heated is used. The shape of each heater 40 is not particularly limited, but may be, for example, a rod shape. By controlling the amount of heat generation of each heater 40, the temperature distribution of the glass ribbon 6 is controlled. The plurality of controllers 50 are devices that control the amount of heat generation of the plurality of heaters 40. Each controller 50 is configured by a microcomputer or the like.

  The float glass manufacturing apparatus 10 is provided with a plurality of pairs of top rolls 60 (see FIG. 3) which are spaced along the flow direction of the glass ribbon 6 and support both widthwise ends of the glass ribbon 6. The plurality of pairs of top rolls 60 support both widthwise end portions of the glass ribbon 6 to suppress narrowing of the width of the glass ribbon 6 due to surface tension. Each top roll 60 is formed of a disk-shaped top roll main body 61 supporting an end in the width direction of the glass ribbon 6 and a rotation shaft 62 connected to the top roll main body 61. The disk-shaped top roll main body 61 and the rotating shaft 62 are provided coaxially. When the rotation shaft 62 is rotationally driven by a driving device such as an electric motor, the top roll main body 61 rotates and feeds the glass ribbon 6 to the downstream side.

(Tub)
As shown in FIG. 3, the bathtub 20 has a narrow area A1 in which the widthwise dimension of the bathtub 20 is constant from the downstream end to the upstream side, an intermediate area A2 in which the widthwise dimension of the bathtub 20 gradually increases, a bathtub In this order, the wide area A3 has a width direction dimension of 20 larger and constant than the narrow area A1. The X-direction dimension X1 of the wide area A3 is, for example, 30% or more and 80% or less of the X-direction dimension X0 of the molten metal 2 accommodated in the bath 20.

The plurality of pairs of top rolls 60 support both widthwise ends of the glass ribbon 6 in the wide area A3. The contact point between each top roll main body 61 and the glass ribbon 6 is provided at a distance from the upstream end of the forming area A4 to the downstream end of the forming area A4. The forming area A4 is an area in which 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 dPa · s or less.

  As shown in FIG. 2, the bathtub 20 is placed on a box-shaped metal casing 21, a plurality of side bricks 22 placed on the bottom of the metal casing 21 and in contact with the side of the molten metal 2, and a bottom of the metal casing 21. And a plurality of bottom bricks 23 in contact with the lower surface of the molten metal 2. The plurality of side bricks 22 are arranged close to the side of the metal casing 21, and the plurality of bottom bricks 23 are arranged inside the plurality of side bricks 22 in the X direction and the Y direction.

  A joint 24 is formed between the bottom bricks 23 adjacent in the Y direction. The joint 24 is a gap. It is difficult to prevent the flow of the molten metal 2 into the joint 24. The molten metal 2 flowing into the joint 24 reaches the bottom of the metal casing 21.

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

  FIG. 4 is a cross-sectional view showing the depth of the molten metal according to the first embodiment. In FIG. 4, the lower part of the metal casing 21 and the bottom brick 23 is omitted. In the present specification, the depth D of the molten metal 2 refers to the distance from the liquid surface (upper surface) of the molten metal 2 to the upper surface of the bottom brick 23 as shown in FIG. 22 (more specifically, in the width direction outside of the glass ribbon 6 and in the width direction of the side bricks 22).

  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. The purpose is to minimize the amount of molten metal 2 used and to reduce the manufacturing cost of float glass.

In the present embodiment, the depth D0 (see FIG. 4) of the molten metal 2 in the forming area A4 is set based on the transport speed V of the glass ribbon 6 in the lehr 70 and is set to satisfy the following formula (1) .
D0 ≧ 1.0 × V + 30 (1)
In the above formula (1), the unit of D0 is mm, and the unit of V is m / min. V is set in accordance with the thickness of the float glass and the like, and is, for example, 3 to 11 m / min. D0 is, for example, 35 to 60 mm. Preferably, V is 4 to 8 m / min and D0 is 35 to 50 mm. More preferably, D0 is 35-45 mm.

  When the above equation (1) is satisfied, the flow velocity of the molten metal 2 flowing back as shown by the arrow C in FIG. 3 can be reduced in the forming area A4 for adjusting the size and shape of the glass ribbon 6. As a result, it is possible to suppress the collapse of the dimensions and the shape of the glass ribbon 6 due to the backflow of the molten metal 2, and it is possible to obtain float glass having a large size and a small plate thickness deviation.

  First, the reason why the backflow of the molten metal 2 shown by the arrow C in FIG. 3 will be described. When the glass ribbon 6 is conveyed at the conveyance speed V in the lehr 70, the glass ribbon 6 flows on the molten metal 2 toward the lehr 70 at the same speed as the conveyance speed V downstream of the forming area A4. At this time, the molten metal 2 immediately below the glass ribbon 6 is dragged by the glass ribbon 6 and flows toward the lehr 70 at the same speed as the glass ribbon 6. The flow of the molten metal 2 is interrupted at the downstream end of the bath 20 and reverses direction. As a result, backflow of the molten metal 2 occurs on the outside in the width direction of the glass ribbon 6.

  Next, the backflow volume flow Q of the molten metal 2 will be described. Backflow of the molten metal 2 is caused by the glass ribbon 6 dragging the molten metal 2 as described above. Therefore, the volumetric flow rate Q is proportional to the transport velocity V of the glass ribbon 6 and the width direction dimension of the glass ribbon 6. The volumetric flow rate Q hardly depends on the depth D of the molten metal 2. The molten metal 2 is dragged to the glass ribbon 6 only for the portion in the vicinity of the glass ribbon 6.

Next, the reverse flow velocity u of the molten metal 2 will be described. In general, the product of the flow velocity u and the cross-sectional area SA is the volumetric flow rate Q (= u × SA). Here, the unit of Q is m ³ / s, the unit of u is m / s, and the unit of SA is m ² . The cross-sectional area SA of the backflowing flow path of the molten metal 2 is the product of the depth D of the molten metal 2 (see FIG. 2) and the distance W in the Y direction between the glass ribbon 6 and the side bricks 22 (see FIG. 2). It is represented by 2 times (SA = D x W x 2 x 10 ^-3 ). The unit of D in this formula is mm, and the unit of W is m. The product of D and W is doubled because the backflow channels of the molten metal 2 are provided on both sides of the glass ribbon 6 in the width direction. Then, the volumetric flow rate Q = u x D x W x 2 x 10 ^-3 . On the other hand, the volumetric flow rate Q is proportional to the transport speed V of the glass ribbon 6 as described above. Therefore, it can be seen that the flow velocity u is proportional to V / D when W is constant.

  The inventor pays attention to the fact that the flow velocity u is proportional to V / D, and expresses the relationship between V and D for suppressing the collapse of the size and shape of the glass ribbon 6 due to the backflow of the molten metal 2 by a linear equation. The relational expression of the above-mentioned formula (1) was obtained by experiment etc. thinking that it can be done. Specific experiments will be described in the section of Examples.

  When the above equation (1) is established, the backflowing flow velocity u of the molten metal 2 shown by the arrow C in FIG. 3 can be reduced in the forming area A4 for adjusting the size and shape of the glass ribbon 6 as described above. As a result, it is possible to suppress the collapse of the dimensions and the shape of the glass ribbon 6 due to the backflow of the molten metal 2, and it is possible to obtain float glass having a large size and a small plate thickness deviation.

  This effect is more remarkably obtained as the widthwise dimension of the glass ribbon 6 is larger. The backflowing volumetric flow rate Q of the molten metal 2 is proportional to the widthwise dimension of the glass ribbon 6. According to the present embodiment, it is a float glass having a longitudinal dimension of 2100 mm or more, a lateral dimension of 2200 mm or more, and an average plate thickness of 0.75 mm or less in plan view, and is the maximum value of the plate thickness in the entire plane. The float glass having a difference of less than 12 μm is obtained. Here, the longitudinal dimension is the dimension in the short side direction of the float glass having a rectangular shape in plan view, and the lateral dimension is the dimension in the longitudinal direction of the float glass having a rectangular shape in plan view. Planar view means viewing in the Z direction in FIG.

  In the present embodiment, the depth D1 (see FIG. 4) of the molten metal 2 in the HOT region A5 (see FIG. 4) is, for example, not less than 1.6 times and 2.0 times the depth D0 of the molten metal 2 in the forming area A4. It is below. The HOT area A5 is an area where the molten glass 4 spreads on the molten metal 2 by gravity. The contact of the molten glass 4 and the bottom brick 23 by pouring of the molten glass 4 can be suppressed as D1 is 1.6 times or more of D0. Moreover, use of the useless molten metal 2 can be suppressed as D1 is 2.0 times or less of D0, and the manufacturing cost of float glass can be reduced.

  In the present embodiment, the depth D2 (see FIG. 4) of the molten metal 2 at the upstream end of the narrow area A1 (see FIG. 4) is, for example, 2.0 times or more 2 times the depth D0 of the molten metal 2 in the forming zone A4. .5 times or less. When D2 is 2.0 times or more of D0, the depth D of the molten metal 2 having a high thermal conductivity becomes deeper, and the thickness of the bottom brick 23 having a low thermal conductivity becomes thinner. The glass ribbon 6 is easy to cool and harden by the cooling nozzle 25 (see FIGS. 1 and 2) installed in the Moreover, use of the useless molten metal 2 can be suppressed as D2 is 2.5 times or less of D0, and the manufacturing cost of float glass can be reduced.

  FIG. 5 is a plan view showing a bathtub, a glass ribbon, a top roll and a barrier according to a modification. 6 is a cross-sectional view of the barrier shown in FIG. The bathtub 20 shown in FIGS. 5 and 6 differs from the bathtub 20 shown in FIG. 4 in that the barrier 27 is removably attached. The differences will be mainly described below.

  The barrier 27 interrupts the flow of the molten metal 2 on the molten metal 2 in the width direction outer side of the glass ribbon 6, and reduces the backflowing flow velocity of the molten metal 2 in the forming area A4. As a result, the collapse 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 having a small thickness deviation can be obtained. The barrier 27 may be provided downstream of the forming area A4 in the wide area A3 as shown in FIG.

  The barrier 27 is provided over the entire Z direction of the molten metal 2 from the upper surface of the bottom brick 23 to the liquid surface of the molten metal 2 and further protrudes upward from the liquid surface of the molten metal 2 as shown in FIG. Be The barrier 27 may be provided only in a part of the molten metal 2 in the Z direction. In that case, the barrier 27 may be provided in contact with the top surface of the bottom brick 23. The backflow of the molten metal 2 is likely to occur in the area away from the glass ribbon 6 which drags the molten metal 2 and is likely to occur near the upper surface of the bottom brick 23.

  The barrier 27 is formed of, for example, carbon, and is immersed in the molten metal 2. When the density of the barrier 27 is lower than the density of the molten metal 2, a pressing member 28 (see FIG. 6) may be fixed to the side brick 22 to hold the barrier 27 so that the barrier 27 does not lift up due to the density difference.

(heater)
FIG. 7 is a plan view showing the arrangement of heater control sections according to one embodiment. FIG. 7 illustrates the arrangement of the heater control sections in the wide area A3, and the illustration of the arrangement of the heater control sections in the intermediate area A2 and the narrow area A1 is omitted. The heater 40 may be provided not only in the wide area A3 but also in the middle area A2 and the narrow area A1.

  As shown in FIG. 7, the heater area in which the plurality of heaters 40 are provided is divided into a plurality of heater control rows 41 in the X direction. Each heater control column 41 is divided into a plurality of heater control sections 42 in the Y direction. The number of heater control rows 41 is not limited to that shown in FIG. Further, the number of heater control sections 42 in each heater control column 41 is not limited to that shown in FIG. 7.

  Each heater control section 42 is provided with a plurality of heaters 40 and collectively controlled by one corresponding controller 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 a corresponding one controller 50 so that their calorific values 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 approximately at the center between the actual heaters 40 adjacent in the X direction. On the other hand, two heater control sections 42 adjacent to each other in the Y direction are divided by one section line 46. The dividing line 46 is located approximately at the center between the actual heaters 40 adjacent in the Y direction.

  By the way, if the calorific value per unit area is different between two heater control sections 42 adjacent to each other in the Y direction in one heater control row 41, a rapid temperature change occurs in the Y direction in the vicinity of the section line 46.

  Therefore, in the present embodiment, in at least one dividing line 45, the dividing line 46 of the heater control line 41 on the upstream side and the dividing line 46 of the heater control line 41 on the downstream side are discontinuous at one or more points. , Offset at one or more points. For example, in the mth dividing line 45-m from the upstream side (left side in FIG. 7), the dividing line 46 of the mth heater control column 41-m from the upstream side and the m + 1th heater control column 41- from the upstream side The m + 1 dividing line 46 is discontinuous at one or more points and deviates at one or more points. Here, m is at least one natural number of 1 or more, and is, for example, any natural number of 1 or more and 6 or less in FIG.

  In the m-th heater control row 41-m of the glass ribbon 6, the portion passing below the dividing line 46 where the temperature change is rapid is heater control where the temperature change is gradual in the m + 1st heater control row 41-m + 1 Pass under the compartment 42. Therefore, the temperature nonuniformity in the Y direction of the glass ribbon 6 can be suppressed, and the plate thickness nonuniformity in the Y direction of the glass ribbon 6 can be reduced.

  In the present embodiment, the dividing line 46 of the heater control line 41 on the upstream side and the dividing line 46 of the heater control line 41 on the downstream side are at least one dividing line 45 in the wide area A3 in the Z direction. It is discontinuous at one or more locations and deviates at one or more locations. The wide area A3 is at a higher temperature than the middle area A2 and the narrow area A1, and adjustment of the size and shape of the glass ribbon 6 is performed in the wide area A3. In the middle area A2 and the narrow area A1, since the viscosity of the glass ribbon 6 is high, it is difficult to adjust the size and the shape of the glass ribbon 6.

  In the present embodiment, the dividing line 46 of the heater control row 41 on the upstream side and the dividing line 46 of the heater control row 41 on the downstream side are at least one dividing line 45 in the forming area A4 in the Z direction. It is discontinuous at one or more locations and deviates at one or more locations. It is because adjustment of the dimension and shape of the glass ribbon 6 is performed using the top roll 60 in the forming area A4 among the wide area A3.

  In each heater control column 41, the plurality of dividing lines 46 may be provided in line symmetry about the Y-direction center line 20L of the bathtub 20. Thereby, the temperature distribution of the molten metal 2 and hence the temperature distribution of the glass ribbon 6 can be made line symmetrical about the Y-direction center line 20L of the bath 20. As a result, control of the thickness distribution of the glass ribbon 6 is easy.

(Float glass)
The float glass has a rectangular shape in plan view, a longitudinal dimension of at least 2100 mm, a transverse dimension of at least 2200 mm, and an average thickness of at most 0.75 mm. 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. If this float glass is used for the glass substrate for FPD, the thickness deviation in the whole surface of a large area can be reduced, and the focus shift of the exposure device can be suppressed. The float glass having a rectangular shape in plan view includes float glass whose corner portion is ground by a grindstone for corner cut. This grinding portion is called a corner cut portion, and the size of the corner cut portion is, for example, several mm.

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

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

The float glass is, for example, SiO ₂ : 54 to 66%, Al ₂ O ₃ : 10 to 23%, B ₂ O ₃ : 0 to 12%, MgO: 0 to 12% in terms of mass% on an oxide basis. It is comprised with non-alkali glass containing CaO: 0-15%, SrO: 0-16%, BaO: 0-15%, MgO + CaO + SrO + BaO: 8-26%. Here, “MgO + CaO + SrO + BaO” means the total content of MgO, CaO, SrO and BaO. Further, “alkali-free glass” means that the total content of alkali metal oxides such as Li ₂ O, Na ₂ O and K ₂ O is less than 0.1% by mass. Preferably, the alkali-free glass has a content of B ₂ O ₃ of 5% or less in mass% display based on the oxide.

  Hereinafter, the present invention will be further described using examples and comparative examples. The present invention is not limited to these descriptions. In the embodiment and the comparative example, the vertical direction corresponds to the X direction, and the horizontal direction corresponds to the Y direction.

  FIG. 8 is a view showing the relationship between the transport 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. 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.

[Examples 1 to 5]
In Example 1, the glass ribbon 6 having a width direction dimension of 4000 mm or more was manufactured using the float glass manufacturing apparatus 10 having the bathtub 20 shown in FIGS. 3 and 4. The glass material 1 shown in Table 2 was used as the glass material which is a raw material of the glass ribbon. Depth D0 in forming area A4 of molten tin which is molten metal 2 was 38 mm. Moreover, the conveyance speed V of the glass ribbon 6 in the slow cooling furnace 70 was 4.2 m / min.

  From the manufactured glass ribbon 6, float glass with a lateral dimension of 2500 mm and float glass with a lateral dimension of 3500 mm were cut out. Each float glass was cut out in left-right symmetry about the width direction center line of the glass ribbon. The average thickness of each float glass was 0.50 mm.

  In Examples 2 to 4, the use amount of molten tin is increased or decreased to change the depth D0 of the molten tin in the forming area A4 to 37 mm, 39 mm, and 40 mm, and the conveying speed of the glass ribbon 6 in the annealing furnace 70 A float glass was obtained under the same conditions as in Example 1 except that V was increased and settings were changed to 4.9 m / min, 5.3 m / min, and 6.7 m / min.

  In the fifth embodiment, the glass material 3 shown in Table 2 is used as the glass material, the amount of molten tin used is increased, and the depth D0 of the molten tin in the forming area A4 is changed to 45 mm. The float glass was obtained under the same conditions as in Example 1 except that the transport speed V was increased and the setting was changed to 10 m / min.

Comparative Examples 1 to 3
In Comparative Example 1, the amount of molten tin used is reduced to change the setting of the depth D0 of the molten tin in the forming area A4 to 33 mm, and the conveyance speed V of the glass ribbon 6 in the lehr 70 is increased to 4.9 m / A float glass was obtained under the same conditions as in Example 1 except that the setting was changed to min.

  In Comparative Example 2, the glass material 2 shown in Table 2 is used as the glass material, the amount of molten tin used is reduced, and the depth D0 in the forming area A4 of molten tin is changed to 35.5 mm, and the glass ribbon in the lehr 70 is used. A float glass was obtained under the same conditions as in Example 1 except that the conveyance speed V of 6 was increased to change the setting to 7.6 m / min.

  In Comparative Example 3, float glass was used under the same conditions as Example 1, except that the glass material 3 shown in Table 2 was used as the glass material, and the conveyance speed V of the glass ribbon 6 in the slow cooling furnace 70 was increased to change it to 10.3 m / min. I got

[Summary]
As is clear from Table 1 and FIG. 8, in Examples 1 to 5, unlike in Comparative Examples 1 to 3, conditions were satisfied to satisfy the above equation (1), so a large float glass having a small thickness deviation was obtained. I was able to get it. Specifically, in the float glass with a lateral dimension of 2500 mm and the float glass with a lateral dimension of 3500 mm, the thickness deviation was 12 μm or less.

  Although the embodiments of the float glass manufacturing method and the float glass and the like have been described above, the present invention is not limited to the above embodiments and the like, and various modifications may be made within the scope of the present invention described in the claims. Modifications and improvements are possible.

DESCRIPTION OF SYMBOLS 10 float glass manufacturing apparatus 20 bathtub 21 metal casing 22 side brick 23 bottom brick 25 cooling nozzle 30 ceiling 40 heater 41 heater control row 42 heater control section 45 dividing line 46 dividing line 50 controller 60 top roll 70 slow cooling furnace

Claims (11)

Molten glass is continuously supplied onto molten metal in a bath, formed into a glass ribbon while flowing the molten glass on the molten metal, and floated to be gradually cooled while conveying the glass ribbon in a lehr. A glass manufacturing method,
When a region having a viscosity of 10 ^4.5 dPa · s to 10 ^7.5 dPa · s at the center in the width direction of the glass ribbon on the molten metal is referred to as a forming region,
The depth of the molten metal in the forming region is D0 (unit: mm), and the transport speed of the glass ribbon in the slow cooling furnace is V (unit: m / min), and the following formula (1) is satisfied. Float glass manufacturing method.
D0 ≧ 1.0 × V + 30 (1)   The float glass manufacturing method of Claim 1 whose said conveyance speed V is 3-11 m / min.   The float glass manufacturing method of Claim 1 or 2 whose said depth D0 is 35-60 mm.   The float glass manufacturing method as described in any one of Claims 1-3 whose said conveyance speed V is 4-8 m / min and whose said depth D0 is 35-50 mm.   The float glass manufacturing method as described in any one of Claims 1-4 which interrupt | block the flow of the said molten metal with the barrier immersed by the said molten metal in the width direction outer side of the said glass ribbon on the said molten metal.   A plurality of heater regions provided with a plurality of heaters provided above the molten metal are divided into a plurality of rows in the flow direction of the glass ribbon, and each row is divided in the width direction of the glass ribbon. The float glass manufacturing method as described in any one of Claims 1-5 which controls the said heater by a controller. A float glass having a longitudinal dimension of at least 2100 mm, a transverse dimension of at least 2200 mm, and an average thickness of at most 0.75 mm, which is rectangular in plan view,
A float glass characterized in that the difference between the maximum value and the minimum value of plate thickness in the entire surface is 12 μm or less.   The float glass according to claim 7, having a longitudinal dimension of 2900 mm or more and a lateral dimension of 3000 mm or more.   The float glass according to claim 7 or 8, wherein the average plate thickness is 0.45 mm or less. In mass% display of oxide standard,
SiO ₂ : 54 to 66%
Al ₂ O ₃ : 10 to 23%
B ₂ O ₃ : 0 to 12%
MgO: 0 to 12%
CaO: 0 to 15%
SrO: 0 to 16%
BaO: 0 to 15%
MgO + CaO + SrO + BaO: 8 to 26%
The float glass according to any one of claims 7 to 9, which is composed of an alkali-free glass containing The float glass according to claim 10, wherein the alkali-free glass has a content of B ₂ O ₃ of 5% or less in terms of mass% on the basis of an oxide.

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