Abstract:
A method of manufacturing a glass sheet includes creating split flows of molten glass in a forming body ( 10 ) and causing the molten glass to flow down, subsequently merging the flows at a merging point to form a glass sheet G and causing the glass sheet to flow downward in the vertical direction. A plurality of chambers ( 42   b   , 42   c , . . . ) separated by heat-insulating plates ( 40   a   , 40   b , . . . ) in the direction of movement of the glass sheet G are provided. A heater ( 60   a   , 60   b , . . . ) is provided for each of the chambers ( 42   b   , 42   c , . . . ) so that the temperature decreases in the direction of movement. The heat-insulating plates ( 40   a   , 40   b , . . . ) are disposed facing the glass sheet G, and facing surfaces of the heat-insulating plates ( 40   a   , 40   b , . . . ) are shaped so as to correspond to a sheet thickness variation of the glass sheet G.

Description:
This is a Continuation of Application No. PCT/JP2011/072481 filed Sep. 29, 2011, which claims benefit to Japanese Patent Application No. 2010-223087 filed Sep. 30, 2010. All of the above-noted applications are incorporated herein by reference in their entirety. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a method of manufacturing a glass sheet. 
     BACKGROUND ART 
     A downdraw method has conventionally been used as one method of manufacturing a glass sheet. In the downdraw method, split flows of molten glass which overflows from a forming body is created so that the molten glass flows down along the surface of the forming body. The two streams of molten glass are then merged at the lower end of the forming body to form a glass sheet. The glass sheet thus formed is annealed while being conveyed downward. In the annealing process, the glass sheet transitions from a viscous stage to an elastic stage via a viscoelastic stage. 
     SUMMARY OF INVENTION 
     Technical Problem 
     In an apparatus for manufacturing a glass sheet by the downdraw method, an annealing zone, which is a space in which the glass sheet separated from the forming body is cooled without touching anything, is usually partitioned into a plurality of annealing spaces by heat-insulating plates. The heat-insulating plates suppress the movement of heat between the annealing spaces, and are provided to control the atmospheric temperature of each annealing space so that a desired temperature profile is obtained. Here, the desired temperature profile is a temperature distribution in the annealing spaces of the annealing zone so that no distortion occurs in the glass sheet. Specifically, by the heat-insulating plates, the glass sheet is adjusted to the desired temperature in each annealing space while being conveyed downward. The heat-insulating plates are thus highly important for annealing the glass sheet so that the glass sheet is formed with minimal distortion. 
     However, the thickness of the glass sheet annealed in the annealing zone is usually greater at both width-direction end portions than at the width-direction center portion. Therefore, in a case in which a glass sheet is held between a pair of heat-insulating plates formed by a single sheet, as disclosed in Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2008-88005), the size of the gap between the pair of heat-insulating plates must be set at least so that the end portions in the width direction of the glass sheet, which are the thickest parts thereof, do not touch the heat-insulating plates. However, heat exchange through the gaps between the annealing spaces increases the larger the gaps are, and the problem emerges that it becomes difficult to control the atmospheric temperatures of the annealing zones so that the desired temperature profile is obtained. 
     Techniques have been used in the past for managing heat by partitioning the annealing zone into a plurality of annealing spaces using heat-insulating plates. 
     For glass substrates used in liquid crystal display devices, required specs (quality) relating to glass sheet thickness deviation, warping, distortion, and the like have become stricter in recent years. 
     In the case of manufacturing glass sheets by the downdraw method as described above, in order to reduce thickness deviation, warping, and distortion of the glass, a desired temperature profile is designed in advance for the annealing spaces, and heat is managed for the atmosphere so that the designed temperature profile is achieved. 
     The precision of the designed temperature profile must be increased in order to satisfy the recent stricter spec requirements, and there is therefore a need to increase the precision of heat management. 
     An object of the present invention is to provide an improved apparatus for manufacturing a glass sheet, in which the precision of heat management can be increased in the manufacture of a glass sheet by a downdraw method, and to provide a method of manufacturing a glass sheet in which the precision of heat management is increased. 
     An object of the present invention is more specifically to provide a glass sheet manufacturing method in which the precision of heat management is increased to suppress distortion in the glass sheet; to provide a glass sheet manufactured using the glass sheet manufacturing method; and to provide a glass sheet manufacturing apparatus capable of suppressing distortion in the glass sheet. 
     Solution to Problem 
     A method of manufacturing a glass sheet according to the present invention is a method of manufacturing a glass sheet, the method comprising the steps of creating split flows of molten glass in a forming body and causing the molten glass to flow down, subsequently merging the flows at a merging point to form a glass sheet, and causing the glass sheet to flow downward in the vertical direction. In this method of manufacturing a glass sheet, there are provided a plurality of chambers separated by heat-insulating plates in the direction of movement of the glass sheet. Also in this method of manufacturing a glass sheet, a heater for controlling the temperature of the chamber is provided for each of the chambers so that the temperature of the chamber decreases in order in the direction of movement of the glass sheet. The heat-insulating plate is disposed facing the glass sheet, and a facing surface of the heat-insulating plate is shaped so as to correspond to a sheet thickness variation of the glass sheet, so that a gap between the glass sheet and the heat-insulating plate is substantially uniform. 
     In the process of manufacturing a glass sheet by a downdraw method, the atmospheric temperature of the annealing zone, which is the space in which the formed glass sheet is annealed, preferably fits a desired temperature profile from top to bottom. The annealing zone is therefore usually partitioned by a plate-shaped heat-insulating member into a plurality of annealing spaces which are stacked in the vertical direction. The atmospheric temperatures of the annealing spaces are thereby controlled so as to fit the desired temperature profile. 
     In the method of manufacturing a glass sheet according to the present invention, pairs of heat-insulating members are provided on both sides in the thickness direction of the glass sheet at a plurality of height positions in the annealing zone, and each heat-insulating member is composed of a first heat-insulating plate and a second heat-insulating plate. One or both of the first heat-insulating plate and the second heat insulating plate can be moved in the thickness direction (horizontal direction) of the glass sheet so that the gap between each heat-insulating member and the glass sheet can be made as small as possible. For example, the gap between the of first heat-insulating plates facing the width-direction center portion of the glass sheet, at which the thickness of the glass sheet is small, is made smaller than the gap between the pair of second heat-insulating plates facing the width-direction end portions of the glass sheet, at which the thickness of the glass sheet is large. Since the open area of the gap between each pair of heat-insulating members is thereby reduced, the movement of heat between adjacent annealing spaces can be suppressed as much as possible. Consequently, in the method of manufacturing a glass sheet according to the present invention, the atmospheric temperatures of the annealing spaces can be controlled to fit the desired temperature profile, and the glass sheet can therefore be annealed so as to be formed with minimal distortion. 
     In the method of manufacturing a glass sheet according to the present invention, the facing surface of the heat-insulating plate is preferably shaped so as to correspond to the sheet thickness variation of the glass sheet, so that the gap between the glass sheet and the heat-insulating plate decreases. Since the open area of the gap between the glass sheet and the heat-insulating member is further reduced by this heat-insulating member, movement of heat from the forming body accommodating part to the forming zone can be more effectively suppressed. 
     In the method of manufacturing a glass sheet according to the present invention, the sheet thickness of the glass sheet is preferably greater at both end portions thereof than at a center portion thereof. 
     In the method of manufacturing a glass sheet according to the present invention, the heat-insulating plate preferably has members which are independent of each other and correspond to a center portion and both end portions of the glass sheet. 
     In the method of manufacturing a glass sheet according to the present invention, the members preferably separate from and come close to the glass sheet. 
     Advantageous Effects of Invention 
     The present invention can provide an improved apparatus for manufacturing a glass sheet, in which the precision of heat management can be increased in the manufacture of a glass sheet by a downdraw method, and can provide a method of manufacturing a glass sheet in which the precision of heat management is increased. 
     More specifically, the present invention can provide a glass sheet manufacturing method in which distortion of a glass sheet can be suppressed; a glass sheet manufactured using the glass sheet manufacturing method; and an apparatus for manufacturing a glass sheet, capable of suppressing distortion of a glass sheet. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a view summarizing the configuration of the glass sheet manufacturing apparatus; 
         FIG. 2  is a schematic sectional view showing the forming device; 
         FIG. 3  is a schematic side view showing the forming device; 
         FIG. 4  is a schematic top view showing the heat-insulating member; 
         FIG. 5  is a schematic side view showing the heat-insulating member; 
         FIG. 6  is a schematic view showing the pair of heat-insulating members with the glass sheet therebetween in plan view; 
         FIG. 7  is a schematic side view showing the heat-insulating member in Modification D; and 
         FIG. 8  is a schematic top view showing the heat-insulating member in Modification I. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     (1) Overall Configuration 
     The general configuration of the glass sheet manufacturing apparatus  100  according to an embodiment of the present invention will first be described. As shown in  FIG. 1 , the glass sheet manufacturing apparatus  100  is composed of a melting furnace  200 , a refining furnace  300 , and a forming device  400 . In the melting furnace  200 , raw materials for glass are melted to create molten glass. The molten glass created in the melting furnace  200  is sent to the refining furnace  300 . Air bubbles in the molten glass are removed in the refining furnace  300 . The molten glass from which air bubbles have been removed by the refining furnace  300  is sent to the forming device  400 . In the forming device  400 , a glass sheet G is continuously formed from the molten glass by an overflow downdraw method. The glass sheet G thus formed is then annealed and cut into glass sheets of a predetermined size. The glass sheets are used as glass substrates for liquid crystal displays and/or plasma displays and other flat-panel displays. 
     The detailed configuration of the forming device  400  will next be described. 
     (2) Detailed Configuration of the Forming Device 
     The forming device  400  is composed of a forming body  10 , partition members  20 , cooling rollers  30 , heat-insulating plates  40   a ,  40   b , and so on, feed rollers  50   a ,  50   b , and so on, and temperature control units  60   a ,  60   b , and so on. As shown in  FIGS. 2 and 3 , the forming device  400  has a forming body accommodating part  410  which is a space above the partition members  20 ; a forming zone  42   a  which is a space immediately below the partition members  20 ; and an annealing zone  420  which is a space below the forming zone  42   a . The annealing zone  420  has a plurality of annealing spaces  42   b ,  42   c , and so on. The forming zone  42   a , annealing space  42   b , annealing space  42   c , and so on are stacked in the stated order top-downward in the vertical direction. 
     (2-1) Forming Body 
     As shown in  FIG. 2 , the forming body  10  is a member having a substantially wedge-shaped cross-section. The forming body  10  is disposed in the forming body accommodating part  410  so that the point of the wedge shape is at the lower end thereof. As shown in  FIG. 3 , a groove  12  is formed in an upper end surface of the forming body  10 . The groove  12  is formed in the longitudinal direction of the forming body  10 . A glass supply tube  14  is provided at one end of the groove  12 . The groove  12  is formed so as to gradually decrease in depth from the one end thereof, at which the glass supply tube  14  is provided, to the other end. 
     (2-2) Partition Members 
     The partition members  20  are plate-shaped heat-insulating members disposed in the vicinity of the lower end of the forming body  10 . The partition members  20  are disposed so that the height position of the lower ends thereof is in the range from the height position of the lower end of the forming body  10  to a height position 50 mm below the lower end of the forming body  10 . As shown in  FIG. 2 , the partition members  20  are disposed on both sides in the thickness direction of the glass sheet G. The partition members  20  suppress the movement of heat from the forming body accommodating part  410  to the forming zone  42   a  by acting as a partition between the forming body accommodating part  410  and the forming zone  42   a . The positioning of the partition members  20  is adjusted in advance so that the gap between the glass sheet G and the partition members  20  is 10 mm to 50 mm. 
     The forming body accommodating part  410  and the forming zone  42   a  are partitioned from each other by the heat-insulating partition members  20  for the purpose of temperature control, so that the spaces of the forming body accommodating part  410  and forming zone  42   a  do not affect each other as to the temperature thereof. In the manufacture of glass substrates for liquid crystal displays, for example, the partitioning described above is provided in order to maintain the atmosphere of the forming body accommodating part  410  at a temperature of 1,200 to 1,300° C. or higher, and to maintain the atmosphere of the lower space at a temperature of 400 to 700° C. (e.g., 600 to 700° C.). 
     In the manufacture of glass substrates for liquid crystal displays, for example, the atmosphere of the upper space is maintained at a temperature of 1,200° C. to 1,300° C. or higher in order to give the molten glass a low viscosity so that the molten glass spreads over and “wets” the surface of the forming body  10 , and to prevent the width of the molten glass flow on the surface of the forming body  10  from decreasing. 
     In the manufacture of glass substrates for liquid crystal displays, for example, the atmosphere of the lower space is maintained at a temperature of 400 to 700° C. (e.g., 600° C. to 700° C.) in order to rapidly lower the temperature and increase the viscosity of the molten glass flow immediately after the molten glass flows are merged by the forming body  10 , and thereby suppress shrinkage of the molten glass in the width direction due to surface direct force (* 1 ) which acts on the molten glass. 
     (2-3) Cooling Rollers 
     The cooling rollers  30  are disposed in the vicinity of the partition members  20  in the forming zone  42   a . The cooling rollers  30  are disposed on both sides of the glass sheet G in the thickness direction thereof. 
     (2-4) Heat-Insulating Members 
     The heat-insulating members  40   a ,  40   b , and so on are plate-shaped heat-insulating members disposed below the cooling rollers  30  in the annealing zone  420  on both sides of the glass sheet G in the thickness direction thereof. The heat-insulating members  40   a ,  40   b , and so on form the forming zone  42   a  and the annealing spaces  42   b ,  42   c , and so on by partitioning the space below the partition members  20 . For example, as shown in  FIG. 2 , the heat-insulating member  40   a  forms the forming zone  42   a  and the annealing space  42   b , and the heat-insulating member  40   b  forms the annealing space  42   b  and the annealing space  42   c . The heat-insulating members  40   a ,  40   b , and so on suppress the movement of heat between the spaces above and below each heat-insulating member. For example, the heat-insulating member  40   a  suppresses the movement of heat between the forming zone  42   a  and the annealing space  42   b , and the heat-insulating member  40   b  suppresses the movement of heat between the annealing space  42   b  and the annealing space  42   c.    
     The heat-insulating members  40   a ,  40   b , and so on are composed of first heat-insulating plates  40   a   1 ,  40   b   1 , and so on, second heat-insulating plates  40   a   2 ,  40   b   2 , and so on, and second heat-insulating plates  40   a   3 ,  40   b   3 , and so on, respectively. The second heat-insulating plates  40   a   2 ,  40   b   2 , and so on and the second heat-insulating plates  40   a   3 ,  40   b   3 , and so on are disposed near both ends of the first heat-insulating plates  40   a   1 ,  40   b   1 , and so on, respectively, in the width direction of the glass sheet G. For example, in the heat-insulating member  40   b  as shown in  FIGS. 4 and 5 , the second heat-insulating plate  40   b   2  and second heat-insulating plate  40   b   3  are disposed adjacent to both ends of the first heat-insulating plate  40   b   1  in the width direction of the glass sheet G. The first heat-insulating plates  40   a   1 ,  40   b   1 , and so on are fixed in place by beams or the like. The second heat-insulating plates  40   a   2 ,  40   b   2 , and so on and the second heat-insulating plates  40   a   3 ,  40   b   3 , and so on are provided so as to be able to move in the thickness direction of the glass sheet G. The distance between the glass sheet G and the second heat-insulating plates  40   a   2 ,  40   b   2 , and so on and the second heat-insulating plates  40   a   3 ,  40   b   3 , and so on can be adjusted by moving the second heat-insulating plates  40   a   2 ,  40   b   2 , and so on. 
     In the present embodiment, the positions of the first heat-insulating plates  40   a   1 ,  40   b   1 , and so on are fixed in advance and the positions of the second heat-insulating plates  40   a   2 ,  40   b   2 , and so on and the second heat-insulating plates  40   a   3 ,  40   b   3 , and so on are adjusted so that the gap between the glass sheet G and the heat-insulating members  40   a ,  40   b , and so on is 10 mm to 50 mm. 
     (2-5) Feed Rollers 
     The feed rollers  50   a ,  50   b , and so on are disposed in the annealing zone  420  on both sides of the glass sheet G in the thickness direction thereof. The feed rollers  50   a ,  50   b , and so on are disposed in the annealing spaces  42   b ,  42   c , and so on, respectively. For example, the feed rollers  50   a  are disposed in the annealing space  42   b , and the feed rollers  50   b  are disposed in the annealing space  42   c.    
     (2-6) Temperature Control Units 
     The temperature control units  60   a ,  60   b , and so on are disposed in the forming zone  42   a  and the annealing spaces  42   b ,  42   c , and so on, respectively, and measure and control the atmospheric temperatures of the forming zone  42   a  and the annealing spaces  42   b ,  42   c , and so on. The temperature control units  60   a ,  60   b , and so on control the atmospheric temperatures of the forming zone  42   a  and the annealing spaces  42   b ,  42   c , and so on so that the atmospheric temperature in the vicinity of the glass sheet G forms a predetermined temperature distribution (referred to hereinafter as a “temperature profile”) in the width direction of the glass sheet G. 
     (3) Operation 
     (3-1) 
     The process by which the glass sheet G is formed by the forming device  400  is described below. 
     The molten glass created in the melting furnace  200  and divested of air bubbles in the refining furnace  300  is sent to the forming body accommodating part  410  of the forming device  400 . In the forming body accommodating part  410 , the molten glass is fed to the groove  12  of the forming body  10  via the glass supply tube  14 . Molten glass overflowing from the groove  12  forms split flows in the transverse direction of the forming body  10  and flows down along the surfaces of both sides of the forming body  10 . The downward-flowing molten glass merges at the lower end portion of the forming body  10 . The merged molten glass flows downward, continuously forming a plate-shaped glass sheet G. 
     The glass sheet G formed in the forming body accommodating part  410  is sent to the forming zone  42   a  and the annealing zone  420 . 
     The glass sheet G is drawn down by the feed rollers  50   a ,  50   b , and so on of the annealing zone  420 . The glass sheet G drawn down by the feed rollers  50   a ,  50   b , and so on is held between cooled metal cooling rollers  30  only at the area of the glass sheet G near both ends thereof, the cooling rollers  30  being set so that the peripheral speed thereof is less than that of the feed rollers  50   a ,  50   b , and so on in the forming zone  42   a  on the upstream side thereof, and the tendency of the sheet width to decrease due to the surface tension of the glass itself and the downward tension applied by the feed rollers  50   a ,  50   b , and so on is thereby suppressed to some degree. 
     In the forming zone  42   a  and the annealing zone  420 , the temperature profile of the forming zone  42   a  and the annealing spaces  42   b ,  42   c , and so on is controlled by the temperature control units  60   a ,  60   b , and so on. Specifically, the atmospheric temperatures of the forming zone  42   a  and the annealing spaces  42   b ,  42   c , and so on are measured, and the atmospheric temperatures of the forming zone  42   a  and the annealing spaces  42   b ,  42   c , and so on are controlled so that a predetermined temperature profile is obtained. 
     Specifically, by obtaining a predetermined temperature profile in the width direction of the glass sheet G in the forming zone  42   a  and the annealing spaces  42   b ,  42   c , and so on, the thickness of the glass sheet G can be made uniform, and warping and distortion thereof can be reduced. 
     In order to reduce distortion, for example, the glass sheet G formed in the forming body accommodating part  410  and the forming zone  42   a  is preferably uniformly annealed in the annealing zone  420 . 
     Thermal shrinkage of the glass sheet G can also be reduced by obtaining a predetermined temperature profile in the flow direction of the glass sheet G in the forming zone  42   a  and the annealing spaces  42   b ,  42   c , and so on. 
     (3-2) 
     The process of moving the second heat-insulating plates  40   a   2 ,  40   b   2 , and so on and the second heat-insulating plates  40   a   3 ,  40   b   3 , and so on in the thickness direction of the glass sheet G will next be described. As an example,  FIG. 6  is a plan view showing the pair of heat-insulating members  40   b , between which is held the glass sheet G annealed in the annealing zone  420 . The heat-insulating members  40   b  are described below, but this description is also applicable to the heat-insulating members  40   a ,  40   b , and so on. 
     It is preferred that the gap between the heat-insulating members  40   b  and the glass sheet G be as small as possible in order to suppress the movement of heat between the annealing spaces  42   b ,  42   c . However, the glass sheet G annealed in the annealing zone  420  has a cross-sectional shape in which both end parts thereof in the width direction are swollen. In the present embodiment, as shown in  FIG. 6 , the first heat-insulating plates  40   b   1  are fixed so as to be as close as possible to the glass sheet G according to the thickness of the glass sheet G, and the second heat-insulating plates  40   b   2 ,  40   b   3  are moved so as to be as close as possible to the glass sheet G according to the shape of the end portions of the glass sheet G in the width direction. Specifically, the gap between the heat-insulating members  40   b  and the glass sheet G is made as small as possible by adjusting the positions of the second heat-insulating plates  40   b   2 ,  40   b   3  according to the cross-sectional shape of the glass sheet G. Specifically, the positions of the second heat-insulating plates  40   b   2 ,  40   b   3  are adjusted so that the gap between the pair of first heat-insulating plates  40   b   1  facing the thin width-direction center portion of the glass sheet G is smaller than the gap between the pairs of second heat-insulating plate second heat-insulating plates  40   b   2 ,  40   b   3  facing the thick width-direction end portions of the glass sheet G. The open area of the gap between the pair of heat-insulating members  40   b  is thereby reduced. 
     (4) Features 
     In the glass sheet manufacturing apparatus  100  according to the present embodiment, the heat-insulating members  40   a ,  40   b , and so on are composed of first heat-insulating plates  40   a   1 ,  40   b   1 , and so on, second heat-insulating plates  40   a   2 ,  40   b   2 , and so on, and second heat-insulating plates  40   a   3 ,  40   b   3 , and so on, respectively. The first heat-insulating plates  40   a   1 ,  40   b   1 , and so on are fixedly provided, and the second heat-insulating plates  40   a   2 ,  40   b   2 , and so on and second heat-insulating plates  40   a   3 ,  40   b   3 , and so on are provided so as to be able to move in the horizontal direction. 
     The thickness of the glass sheet G annealed in the annealing zone  420  varies in the width direction of the glass sheet G. The thickness of both width-direction end portions of the glass sheet G is generally greater than the thickness of the width-direction center portion thereof. The first heat-insulating plates  40   a   1 ,  40   b   1 , and so on are disposed so as to face the surface of the width-direction center portion of the glass sheet G. The second heat-insulating plates  40   a   2 ,  40   b   2 , and so on and the second heat-insulating plates  40   a   3 ,  40   b   3 , and so on are disposed so as to face the surface of both width-direction end portions of the glass sheet, respectively. The first heat-insulating plates  40   a   1 ,  40   b   1 , and so on are fixed in advance according to the thickness of the glass sheet G, and the second heat-insulating plates  40   a   2 ,  40   b   2 , and so on and second heat-insulating plates  40   a   3 ,  40   b   3 , and so on are moved according to the shape of the width-direction end portions of the glass sheet G. Specifically, the positions of the second heat-insulating plates  40   a   2 ,  40   b   2 , and so on and the second heat-insulating plates  40   a   3 ,  40   b   3 , and so on in the horizontal direction are adjusted so that the respective gaps between the second heat-insulating plates  40   a   2 ,  40   b   2 , and so on and the second heat-insulating plates  40   a   3 ,  40   b   3 , and so on and the glass sheet G are as small as possible. The open area of the gaps between the pairs of heat-insulating members  40   a ,  40   b , and so on can thereby be reduced as much as possible, and the movement of heat between the adjacent forming zone  42   a  and annealing spaces  42   b ,  42   c , and so on can therefore be efficiently suppressed. 
     Consequently, in the glass sheet manufacturing apparatus  100  according to the present embodiment, the atmospheric temperatures of the annealing spaces  42   b ,  42   c , and so on can be controlled so as to fit the desired temperature profile, and the glass sheet can therefore be effectively annealed. Specifically, distortion of the glass sheet can be suppressed in the glass sheet manufacturing apparatus  100  according to the present embodiment. 
     (5) Modifications 
     (5-1) Modification A 
     A glass sheet manufacturing apparatus  100  provided with a forming device  400  for forming a glass sheet G using an overflow downdraw method is described in the present embodiment, but the glass sheet manufacturing apparatus  100  may also be provided with a forming device for forming a glass sheet using a slot downdraw method. 
     (5-2) Modification B 
     The forming device  400  is provided with heat-insulating members  40   a ,  40   b , and so on in the present embodiment, but a glass flow rate control mechanism may be further provided for controlling the flow rate of molten glass supplied to the forming body  10 , so that the thickness of the formed glass sheet G remains constant. 
     In the present modification, the flow rate of molten glass supplied to the forming body  10  is calculated by measuring the weight of the glass sheet G formed by the forming device  400 . The glass flow rate control mechanism controls the flow rate of molten glass by changing the temperature of a molten glass supply tube (not shown in the drawing) installed in the forming device  400  in the case that the calculated flow rate of molten glass is outside a set range. For example, the glass flow rate control mechanism raises the temperature of the molten glass supply tube when the flow rate of molten glass is below the minimum value of the set range. The viscosity of the molten glass in the molten glass supply tube is thereby reduced, and the flow rate of the molten glass supplied to the forming body  10  therefore increases. Conversely, when the flow rate of molten glass is above the maximum value of the set range, the glass flow rate control mechanism lowers the temperature of the molten glass supply tube. The viscosity of the molten glass in the molten glass supply tube is thereby increased, and the flow rate of molten glass supplied to the forming body  10  therefore decreases. Methods for changing the temperature of the molten glass supply tube may include, for example, passing an electric current to the molten glass supply tube to heat the molten glass supply tube and thereby control the temperature of the molten glass supply tube. The glass flow rate control mechanism thus controls the flow rate of molten glass supplied to the forming body  10  by adjusting the temperature of the molten glass supply tube. The flow rate of molten glass can thus be kept constant in the present modification, and the thickness and/or width of the formed glass sheet G can therefore be kept constant. 
     (5-3) Modification C 
     A forming device  400  provided with heat-insulating members  40   a ,  40   b , and so on and a glass flow rate control mechanism is described in Modification C of the present embodiment, but a glass sheet G may also be formed using a forming device that is provided with a glass flow rate control mechanism but not with heat-insulating members  40   a ,  40   b , and so on. 
     (5-4) Modification D 
     In the present embodiment, the second heat-insulating plates  40   a   2 ,  40   b   2 , and so on and the second heat-insulating plates  40   a   3 ,  40   b   3 , and so on are disposed adjacent to either end of the first heat-insulating plates  40   a   1 ,  40   b   1 , and so on, respectively, in the width direction of the glass sheet G, as shown in  FIG. 5 . However, the second heat-insulating plates  40   a   2 ,  40   b   2 , and so on and the second heat-insulating plates  40   a   3 ,  40   b   3 , and so on may also be disposed so as to partially overlap with either end portion of the first heat-insulating plates  40   a   1 ,  40   b   1 , and so on, respectively, in the width direction of the glass sheet G, as shown in  FIG. 7 . 
     (5-5) Modification E 
     In the present embodiment, the first heat-insulating plates  40   a   1 ,  40   b   1 , and so on are fixed in position and the second heat-insulating plates  40   a   2 ,  40   b   2 , and so on and second heat-insulating plates  40   a   3 ,  40   b   3 , and so on are provided so as to be able to move in the thickness direction of the glass sheet G. However, the heat-insulating plates may be configured in any manner insofar as at least one of the first heat-insulating plates  40   a   1 ,  40   b   1 , and so on, the second heat-insulating plates  40   a   2 ,  40   b   2 , and so on, and the second heat-insulating plates  40   a   3 ,  40   b   3 , and so on can move in the thickness direction of the glass sheet G. For example, the second heat-insulating plates  40   a   2 ,  40   b   2 , and so on may be fixed, and the first heat-insulating plates  40   a   1 ,  40   b   1 , and so on may be movably provided. 
     (5-6) Modification F 
     The heat-insulating members  40   a ,  40   b , and so on are each composed of three heat-insulating plates, made up of first heat-insulating plates  40   a   1 ,  40   b   1 , and so on, second heat-insulating plates  40   a   2 ,  40   b   2 , and so on, and second heat-insulating plates  40   a   3 ,  40   b   3 , and so on in the present embodiment, but the heat-insulating members  40   a ,  40   b , and so on may be composed of five, seven, or more heat-insulating plates. 
     In the present modification, the shape of the heat-insulating members  40   a ,  40   b , and so on can be more finely adjusted according to the cross-sectional shape of the glass sheet G. The gaps between the heat-insulating members  40   a ,  40   b , and so on and the glass sheet G can thereby be further reduced, and the movement of heat between adjacent annealing spaces  42   b ,  42   c , and so on can be more efficiently suppressed. Shrinkage of the glass sheet G in the width direction thereof can thus be more efficiently suppressed by the present modification. 
     (5-7) Modification G 
     The heat-insulating members  40   a ,  40   b , and so on are each composed of three heat-insulating plates, made up of first heat-insulating plates  40   a   1 ,  40   b   1 , and so on, second heat-insulating plates  40   a   2 ,  40   b   2 , and so on, and second heat-insulating plates  40   a   3 ,  40   b   3 , and so on in the present embodiment, but the partition members  20  may also be composed of a plurality of plate-shaped components, and some of these components may be provided so as to be able to move in the thickness direction of the glass sheet G. 
     In the present modification, the shapes of the partition members  20  may be changed according to the cross-sectional shape of the glass sheet G moving downward through the forming body accommodating part  410 . For example, a portion of the components constituting the partition members  20  are moved in the thickness direction of the glass sheet G in order to make the gap between the partition members  20  and the glass sheet G as small as possible. The movement of heat between the annealing space  42   a  and the forming body accommodating part  410  adjacent to the partition members  20  can thereby be suppressed. Shrinkage of the glass sheet G in the width direction thereof can thus be more efficiently suppressed in the present modification. 
     (5-8) Modification H 
     The heat-insulating members  40   a ,  40   b , and so on are each composed of three heat-insulating plates, made up of first heat-insulating plates  40   a   1 ,  40   b   1 , and so on, second heat-insulating plates  40   a   2 ,  40   b   2 , and so on, and second heat-insulating plates  40   a   3 ,  40   b   3 , and so on in the present embodiment, but may be composed of a single partition plate which corresponds to a sheet thickness variation of the glass sheet G. 
     (5-9) Modification I 
     In the present embodiment, the heat-insulating members  40   a ,  40   b , and so on are each composed of three heat-insulating plates, made up of first heat-insulating plates  40   a   1 ,  40   b   1 , and so on, second heat-insulating plates  40   a   2 ,  40   b   2 , and so on, and second heat-insulating plates  40   a   3 ,  40   b   3 , and so on, and the second heat-insulating plates  40   a   2 ,  40   b   2 , and so on and the second heat-insulating plates  40   a   3 ,  40   b   3 , and so on are disposed facing the surfaces of both width-direction end portions of the glass sheet G. However, as shown in  FIG. 6 , since the second heat-insulating plates  40   a   2 ,  40   b   2 , and so on and the second heat-insulating plates  40   a   3 ,  40   b   3 , and so on are disposed so that the width thereof exceeds that of the glass sheet G, the portions not occupied by the downflow of the glass sheet G form spaces sandwiched by the end faces of the pairs of second heat-insulating plates  40   a   2 ,  40   b   2 , and so on (or second heat-insulating plates  40   a   3 ,  40   b   3 , and so on). The second heat-insulating plates  40   a   2 ,  40   b   2 , and so on and the second heat-insulating plates  40   a   3 ,  40   b   3 , and so on may therefore further comprise two small heat-insulating plates in order to reduce the amount of the space described above. 
     In the present modification, heat-insulating members  140   a  (the same configuration applying to the other heat-insulating members hereinafter) are each composed of one first heat-insulating plate  140   a   1  and two second heat-insulating plates  140   a   2 ,  140   a   3 , the second heat-insulating plate  140   a   2  is further composed of a first small heat-insulating plate  140   a   21  and a second small heat-insulating plate  140   a   22 , and the second heat-insulating plate  140   a   3  is further composed of a first small heat-insulating plate  140   a   31  and a second small heat-insulating plate  140   a   32 , as shown in  FIG. 8 . In each second heat-insulating plate  140   a   2 , the first small heat-insulating plate  140   a   21  is connected to the second small heat-insulating plate  140   a   22  in the width direction of the glass sheet G. Each first small heat-insulating plate  140   a   21  is connected to a first heat-insulating plate  140   a   1  in the width direction of the glass sheet G. Specifically, each first small heat-insulating plate  140   a   21  is disposed between a first heat-insulating plate  140   a   1  and a second small heat-insulating plate  140   a   22 . Likewise in each second heat-insulating plate  140   a   3 , the first small heat-insulating plate  140   a   31  is disposed between a first heat-insulating plate  140   a   1  and a second small heat-insulating plate  140   a   32 , according to the same configuration as in each second heat-insulating plate  140   a   2 . 
     In the present modification, the first small heat-insulating plates  140   a   21 ,  140   a   31  of the second heat-insulating plates  140   a   2 ,  140   a   3  are disposed facing the surfaces of both width-direction end portions of the glass sheet G, as shown in  FIG. 8 . The second small heat-insulating plates  140   a   22 ,  140   a   32  of the second heat-insulating plates  140   a   2 ,  140   a   3  on one side are disposed facing the second small heat-insulating plates  140   a   22 ,  140   a   32  of the other side. Specifically, the pair of second small heat-insulating plates  140   a   22  (or the pair of second small heat-insulating plates  140   a   32 ) are disposed so that end surfaces thereof touch each other, or so that the end surfaces thereof are extremely close to each other. The open area of the gap between the pair of heat-insulating members  140   a  and the glass sheet G can thereby be more effectively reduced, and the movement of heat between adjacent annealing spaces  42   b ,  42   c , and so on can therefore be more efficiently suppressed. 
     INDUSTRIAL APPLICABILITY 
     By the method of manufacturing a glass sheet according to the present invention, distortion of the glass sheet can be suppressed. 
     REFERENCE SIGNS LIST 
     
         
           10  forming body 
           12  groove 
           14  glass supply tube 
           20  partition members 
           30  cooling rollers 
           40   a ,  40   b , and so on heat-insulating members 
           40   a   1 ,  40   b   1 , and so on first heat-insulating plates 
           40   a   2 ,  40   b   2 , and so on second heat-insulating plates 
           40   a   3 ,  40   b   3 , and so on second heat-insulating plates 
           42   a  forming zone 
           42   b ,  42   c , and so on annealing spaces 
           50   a ,  50   b , and so on feed rollers 
           60   a ,  60   b , and so on temperature control units 
           100  glass sheet manufacturing apparatus 
           200  melting furnace 
           300  refining furnace 
           400  forming device 
           410  forming body accommodating part 
           420  annealing zone 
         G glass sheet 
       
    
     CITATION LIST 
     Patent Literature 
     
         
         
           
             &lt;Patent Document 1&gt; Japanese Unexamined Patent Application Publication No. 2008-88005